U.S. patent application number 09/506279 was filed with the patent office on 2001-12-06 for apparatus and method for multi-zone high-density inductively-coupled plasma generation.
Invention is credited to Moslehi, Mehrdad M..
Application Number | 20010047760 09/506279 |
Document ID | / |
Family ID | 24721236 |
Filed Date | 2001-12-06 |
United States Patent
Application |
20010047760 |
Kind Code |
A1 |
Moslehi, Mehrdad M. |
December 6, 2001 |
Apparatus and method for multi-zone high-density
inductively-coupled plasma generation
Abstract
A multi-zone high-density inductively-coupled plasma source
includes a first individually controlled RF antenna segment for
producing a plasma from a process gas. A second individually
controlled coil segment is included in the ICP source for producing
a plasma from a process gas. In various embodiments, more than two
sets of individually controlled coil segments may be used. In one
embodiment, a separate power supply may be used for each coil
segment individually. Another aspect of this invention is a
hermetically-sealed inductively-coupled plasma source structure and
method of fabrication which eliminates the possibility of process
contamination, improves the source hardware reliability and
functionality, and improves the vacuum integrity and ultimate base
pressure of the plasma system.
Inventors: |
Moslehi, Mehrdad M.; (Los
Altos, CA) |
Correspondence
Address: |
GRAY, CARY, WARE & FREIDENRICH LLP
1221 SOUTH MOPAC EXPRESSWAY
SUITE 400
AUSTIN
TX
78746-6875
US
|
Family ID: |
24721236 |
Appl. No.: |
09/506279 |
Filed: |
February 17, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09506279 |
Feb 17, 2000 |
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08928617 |
Sep 12, 1997 |
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08928617 |
Sep 12, 1997 |
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08678065 |
Jul 10, 1996 |
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5846883 |
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Current U.S.
Class: |
118/723I ;
156/345.48; 438/710 |
Current CPC
Class: |
H01J 37/321
20130101 |
Class at
Publication: |
118/723.00I ;
156/345; 438/710 |
International
Class: |
H01L 021/302 |
Claims
What is claimed is:
1. A multi-zone inductively-coupled plasma source, for producing a
plasma medium comprising: a first antenna structure for
substantially inductive coupling of radio-frequency electrical
power to said plasma medium; at least one additional antenna
structure for inductive coupling of additional radio-frequency
electrical power to said plasma medium, wherein said first antenna
structure and said at least one additional antenna structure are
operated together for providing a substantially uniform plasma
process on at least one substrate placed in a low-pressure plasma
processing equipment.
2. The inductively-coupled plasma source of claim 1, further
comprising; a plurality of radio-frequency power supplies operable
to supply power to said antenna structures; and a real-time
multi-variable controller operable to control the plurality of
radio frequency power supplies in order to provide a substantially
uniform plasma process.
3. The inductively-coupled plasma source of claim 1, further
comprising; a plurality of radio-frequency power supplies operable
to supply power to said antenna structures; and a scalar controller
with pre-specified power supply power ratios operable to control
the plurality of radio frequency power supplies in order to provide
a substantially uniform plasma process.
4. The inductively-coupled plasma source of claim 1 wherein said
first antenna structure comprises at least one antenna segment made
of an electrically conducting material.
5. The inductively-coupled plasma source of claim 1 wherein said
first antenna structure comprises at least two antenna segments
made of an electrically conducting material and further wherein
said at least two antenna segments are connected in series via at
least one series capacitor.
6. The inductively-coupled plasma source of claim 5 wherein said at
least one series capacitor is operable to reduce the induced
radio-frequency voltage across said first antenna structure.
7. The inductively-coupled plasma source of claim 6 wherein said
first antenna segment is shaped as a substantially circular broken
ring.
8. The inductively-coupled plasma source of claim 1 wherein said at
least one additional antenna structure comprises at least one
antenna segment made of an electrically conducting material.
9. The inductively-coupled plasma source of claim 1 wherein said at
least one additional antenna structure comprises at least two
antenna segments made of an electrically conducting material and
further wherein said at least two antenna segments are connected in
series via at least one series capacitor.
10. The inductively-coupled plasma source of claim 9 wherein said
at least one series capacitor is operable to reduce the induced
radio-frequency voltage across said at least one additional antenna
structure.
11. The inductively-coupled plasma source of claim 4 wherein each
of said at least one antenna additional segment has a shape of a
substantially circular broken ring.
12. The inductively-coupled plasma source of claim 1 wherein said
radio-frequency electrical power and said additional
radio-frequency electrical power are supplied by a single
radio-frequency power supply.
13. The inductively-coupled plasma source of claim 12 further
comprising a plurality of adjustable capacitors operable to connect
said antenna structures in parallel to said single radio-frequency
power supply.
14. The inductively-coupled plasma source of claim 12 wherein said
radio-frequency power supply further comprises a radio-frequency
matching network operable to maximize radio-frequency power
coupling efficiency to said antenna structures.
15. The inductively-coupled plasma source of claim 12 further
comprising an adjustable transformer coupling device operable
coupled to the single radio-frequency power supply, and wherein
said adjustable transformer coupling device coupling parameters are
adjusted by a multi-variable controller in order to establish a
substantially uniform plasma process on said at least one
substrate.
16. The inductively-coupled plasma source of claim 15 wherein said
radio-frequency power supply further comprises a radio-frequency
matching network in order to maximize the radio-frequency power
coupling efficiency to said antenna structures.
17. The inductively-coupled plasma source of claim 1 wherein said
first antenna structure and said at least one additional antenna
structure provide a capability to control plasma density values in
different regions of said plasma medium.
18. The inductively-coupled plasma source of claim 13 wherein said
adjustable capacitors are set according to pre-specified values in
order to establish a substantially uniform plasma process on said
at least one substrate.
19. The inductively-coupled plasma source of claim 13 wherein said
adjustable capacitors are adjusted by a multi-variable controller
in order to establish a substantially uniform plasma process on
said at least one substrate.
20. The inductively-coupled plasma source of claim 15 wherein said
adjustable transformer coupling device coupling parameters are set
according to pre-specified values in order to establish a
substantially uniform plasma process on said at least one
substrate.
21. The inductively-coupled plasma source of claim 1 wherein said
radio-frequency electrical power and said additional
radio-frequency power are supplied by at least two separate
radio-frequency power supplies.
22. The inductively-coupled plasma source of claim 21 wherein said
at least two separate radio-frequency power supplies are adjusted
according to pre-specified power set points in order to establish a
substantially uniform plasma process on said at least one
substrate.
23. The inductively-coupled plasma source of claim 21 wherein said
at least two separate radio-frequency power supplies are adjusted
by a multi-variable controller in order to establish a
substantially uniform plasma process on said at least one
substrate.
24. The inductively-coupled plasma source of claim 1 wherein said
plasma processing equipment is a semiconductor device manufacturing
equipment.
25. The inductively-coupled plasma source of claim 1 wherein said
plasma processing equipment is a data storage device manufacturing
equipment.
26. The inductively-coupled plasma source of claim 1 wherein said
first antenna structure comprises a substantially planar
antenna.
27. The inductively-coupled plasma source of claim 1 wherein said
at least one additional antenna structure comprises a substantially
planar antenna.
28. The inductively-coupled plasma source of claim 1 wherein said
first antenna structure comprises a cylindrical antenna and wherein
said at least one additional antenna structure comprises a
cylindrical antenna.
29. The inductively-coupled plasma source of claim 1 wherein said
first antenna structure comprises a conic antenna and wherein said
at least one additional antenna structure comprises a conic
antenna.
30. The inductively-coupled plasma source of claim 1 wherein said
first antenna structure comprises a graded structure antenna and
wherein said at least one additional antenna structure comprises a
graded structure antenna.
31. The inductively-coupled plasma source of claim 1 wherein said
first antenna structure and said at least one additional antenna
structure are embedded in a protective housing made of an
electrically insulating material.
32. The inductively-coupled plasma source of claim 31 wherein said
protective housing is coupled to a vacuum support component
providing vacuum real to process chamber of said plasma processing
equipment.
33. The inductively-coupled plasma source of claim 31 wherein said
protective housing comprises a thermally conducting material.
34. The inductively-coupled plasma source of claim 31 wherein said
electrically insulating material is a ceramic-based material.
35. The inductively-coupled plasma source of claim 34 wherein said
ceramic-based material comprises aluminum nitride.
36. The inductively-coupled plasma source of claim 31 wherein said
electrically insulating material is a polymer-based material.
37. The apparatus of claim 1, further comprising: a first RF power
supply for providing RF power to said first antenna structure; and
at least one separate RF power supply for providing RF power to
said at least one additional antenna structure; said first RF power
supply and said at least one separate RF power supply being
associated to achieve uniform plasma process on said at least one
substrate in said plasma processing equipment.
38. The apparatus of claim 37, wherein said first RF power supply
and said at least one separate RF power supply operate
independently for providing multi-RDMP process control flexibility
and uniformity adjustment during a plasma fabrication process.
39. The apparatus of claim 1, further comprising; a first RF power
supply for providing RF power to said first antenna structure; and
at least one separate RF power supply for providing RF power to
said at least one additional antenna structure; said first RF power
supply and said at least one separate RF power supply being
associated to achieve spatially uniform plasma density and ion
current density in said plasma processing equipment.
40. The inductively-coupled plasma source of claim 1 wherein said
antenna structures comprise a plurality of inductive coil segments
with various sizes a spatial positions selected to provide a
substantially uniform plasma process on said at least one substrate
with a specified substrate size.
41. The inductively-coupled plasma source of claim 1 wherein said
inductive coil segments are formed as substantially concentric
broken circular rights with various diameters.
42. The inductively-coupled plasma source of claim 1 wherein said
inductive coil segments ring breaks are angularly staggered.
43. The inductively-coupled plasma source of claim 1 further
comprising an optical viewport for real-time plasma process
monitoring using an in-situ sensor in said plasma processing
equipment.
44. The inductively-coupled plasma source of claim 43 wherein said
in-situ sensor is a plasma emission sensor.
45. The inductively-coupled plasma source of claim 43 wherein said
in-situ sensor is a full-wafer interferometry sensor.
46. The inductively-coupled plasma source of claim 31 wherein said
protective housing comprises an upper dielectric plate and a lower
dielectric plate.
47. The inductively-coupled plasma source of claim 46 wherein said
upper dielectric plate comprises feedthroughs for providing
electrical connections to said antenna structures.
48. The inductively-coupled plasma source of claim 47 wherein said
upper dielectric plate further comprises at least one process gas
inlet feedthrough and at least one gas dispersion cavity associated
with said process gas inlet feedthrough.
49. The inductively-coupled plasma source of claim 48 wherein said
lower dielectric plate comprises cavities to house said antenna
structures.
50. The inductively-coupled plasma source of claim 49 wherein said
lower dielectric plate further comprises a plurality of small
diameter holes for injecting a process gas from said at least one
gas dispersal cavity.
51. The inductively-coupled plasma source of claim 31 wherein said
protective housing is a substantially planar assembly.
52. The inductively-coupled plasma source of claim 51 wherein said
protective housing is a substantially cylindrical assembly with a
diameter larger than said at least one substrate size.
53. The inductively-coupled plasma source of claim 9 wherein said
at least one series capacitor connecting said at least two antenna
segments is placed outside said plasma processing equipment vacuum
chamber.
54. The inductively-coupled plasma source of claim 1 wherein said
antenna structures have circular antenna segments.
55. The inductively-coupled plasma source of claim 1 wherein said
antenna structures have spiral antenna segments.
56. The inductively-coupled plasma source of claim 1 wherein said
radio frequency electrical power and said additional
radio-frequency electrical power have electrical frequencies in the
range of 1 MHZ to 50 MHZ.
57. The inductively-coupled plasma source of claim 1 wherein said
radio-frequencies electrical power and said additional
radio-frequency electrical power have equal electrical
frequencies.
58. The inductively-coupled plasma source of claim 1 wherein said
antenna structures provide spatial resolution and control
capability within said plasma medium for establishing a multi-zone
adjustment capability for plasma process parameters at said at
least one substrate.
59. A method for producing a multi-zone inductively-coupled plasma
in a plasma processing equipment, comprising the steps of:
producing a plasma from a plasma process gas using a first
inductively-coupled antenna structure; separately producing a
plasma from a plasma process gas using at least one additional
inductively-coupled antenna structure; and operating said first
antenna structure in concert with at least one additional antenna
structure to establish a substantially uniform plasma process on at
least one substrate in said plasma processing equipment.
60. The method of claim 59, further comprising the steps of:
providing radio frequency electrical power to said first
inductively-coupled antenna structure using a first radio frequency
power supply; providing radio frequency electrical power to said at
least one additional inductively-coupled antenna structure using at
least one separate radio frequency power supply; associating said
first radio frequency power supply and said at least one separate
radio frequency power supply for achieving uniform plasma
processing on said at least one substrate.
61. The method of claim 60, further comprising the steps of
independently operating and adjusting said first radio frequency
power supply and said at least one separate radio frequency power
supply to provide process control flexibility and uniformity
adjustment during a plasma process.
62. The method of claim 59, further comprising the steps providing
radio frequency power to said first inductively-coupled antenna
structure and to said at least one additional inductively-coupled
antenna structure using a single radio frequency power supply.
63. The method of claim 62, wherein the step of providing radio
frequency power using a single radio frequency power supply further
comprises adjustably delivering electrical power levels from said
single radio frequency power supply through at least two adjustable
passive electrical components.
64. The method of claim 63, further comprising the step of
independently operating and adjusting the set points for said
adjustable passive electrical components to establish a
substantially uniform plasma process.
65. The method of claim 62, wherein the step of providing radio
frequency power using a single radio frequency power supply further
comprises placing a transformer with adjustable-coupling sections
between said single radio frequency power supply and said first
inductively-coupled antenna structure.
66. The method of claim 65, further comprising the step of
independently operating said transformer and adjusting said
adjustable-coupling sections to establish a substantially uniform
plasma process.
67. The method of claim 59, further comprising the steps of
controlling said at least one additional inductively-coupled
antenna structure to operate as a plurality of individual sets of
inductively coupled antenna segments sized according to the size of
said at least one substrate in said plasma processing
equipment.
68. The method of claim 59, further comprising the step of
minimizing electric field induced arcing in said plasma processing
equipment by reducing radio frequency voltage across said first
inductively-coupled antenna structure and said at least one
additional antenna structure by means of distributed resonant
capacitors in said first inductively-coupled antenna structure and
said at least one additional antenna structure.
69. The method of claim 59, further comprising the steps of
providing real-time multi-zone control of said first
inductively-coupled antenna structure and said at least one
additional inductively-coupled antenna structure using at least one
in situ sensor to probe said plasma processing equipment to
establish a substantially uniform plasma process.
70. The method of claim 60, further comprising the step of sending
a control signal provided by a sensor to a multi-variable
controller to adjust the power supplied by the first radio
frequency power supply and the power supplied by the at least one
additional radio frequency power supply on a run-by-run basis.
71. The method of claim 60, further comprising the step of sending
a control signal provided by a sensor to a multi-variable
controller to adjust the power supplied by the first radio
frequency power supply and the power supplied by the at least one
additional radio frequency power supply on a real time basis.
72. A method for forming a multi-zone high-density
inductively-coupled plasma source, comprising the steps of: forming
a first set of inductively coupled coil segments for producing a
plasma from a plasma process gas; and forming at least one separate
set of inductively-coupled coil segments for separately producing a
plasma from a plasma process gas, said first set of individually
controlled inductively-coupled coil segments and said at least one
separate set of inductively coupled coil segments associated for
spatially resolved multi-zone operation to establish a
substantially uniform plasma process.
73. The method of claim 72, further comprising the steps of:
forming a first radio frequency power supply for providing radio
frequency power to said first set of inductively-coupled coil
segments; and forming at least one separate radio frequency power
supply for providing radio frequency power to said at least one
separate set of inductively-coupled coil segments; said first radio
frequency power supply and said at least one separate radio
frequency power supply formed to achieve uniform plasma density and
ion current density in a semiconductor device plasma fabrication
equipment process environment acting on at least one substrate.
74. The method of claim 74, further comprising the step of
utilizing said first radio frequency power supply and said at least
one separate radio frequency power supply to operate independently
for providing process control flexibility and uniformity adjustment
during a plasma fabrication process.
75. The method of claim 73, further comprising the steps of:
utilizing a first radio frequency power supply for providing radio
frequency power to said first set of inductively-coupled coil
segments; and utilizing at least one separate radio frequency power
supply for providing RF power to said at least one separate set of
inductively-coupled coil segments; said first radio frequency power
supply and said at least one separate radio frequency power supply
being operated to achieve sufficiently intense plasma density and
ion current density in a plasma fabrication process
environment.
76. The method of claim 73, further comprising the step of forming
said at least one separate set of inductively-coupled coil segments
to comprise a plurality of inductively-coupled coil broken rings
sized according to a predetermined substrate size.
77. The method of claim 73, further comprising the step of
interconnecting said inductively-coupled coil segments using at
least one series capacitor to minimize electric field induced
arcing in a plasma fabrication process environment.
78. The method of claim 73, further comprising the step of
utilizing at least one in situ sensor for association within the
plasma fabrication process environment to enable multi-zone control
of said first set of inductively-coupled coil segments and said at
least one separate set of inductively-coupled coil segments.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] This invention relates generally to plasma processing
methods and systems, and more particularly to an apparatus and
method for high-density inductively-coupled plasma generation for
plasma-assisted fabrication processes used for manufacturing of
semiconductor, data storage, flat-panel display, photovoltaic, and
multi-chip module devices.
BACKGROUND OF THE INVENTION
[0002] Plasma processes are used for numerous fabrication steps in
various device manufacturing applications such as semiconductor
integrated circuit, data storage device (heads and media), and
flat-panel display manufacturing. Typically, plasma processes (also
known as plasma-enhanced or plasma-assisted processes) are used for
physical-vapor deposition (PVD), plasma-enhanced chemical-vapor
deposition (PECVD), dry etching, wafer cleaning (or surface
preparation), in-situ chamber cleaning, and plasma-immersion ion
implantation (also known as plasma doping) applications.
Conventional or prior art methods of plasma generation employ one
or a combination of several techniques. Various plasma generation
techniques include parallel-plate capacitive discharge, microwave
discharge (including electron cyclotron resonance or ECR plasma),
hollow cathode discharge, and inductively-coupled plasma (ICP)
sources.
[0003] The high-density inductively-coupled plasma or ICP sources
have recently received a significant amount of attention due to
their superior process performance, throughput rate, and control
capabilities. ICP sources can provide high-density (n.sub.p values
ranging from 1.times.10.sup.11 cm.sup.-3 to over 5.times.10.sup.12
cm.sup.-3) plasmas using fairly simple inductive radio frequency
(RF) excitation. Advanced ICP source designs are capable of
producing fairly high plasma densities (corresponding to the plasma
electron density or n.sub.p) even larger than 1.times.10.sup.13
cm.sup.-3. The RF source frequency is typically in the range of 1
to 30 MHZ (with a preference for 13.56 MHZ). RF frequencies in the
low end of this range result in reduced induced RF voltages across
the ICP antenna. This reduces the risk of capacitive coupling as
well as sputtering of the inner process chamber and ICP source
walls near the ICP antenna. Lower ICP source frequencies, however,
result in reduced plasma densities and larger RF matching network
components. On the other hand, higher RF frequencies can provide
superior plasma densities and can be effectively coupled to the
plasma load using more compact RF matching network components.
However, precautions must be taken to ensure that no chamber wall
sputtering occurs due to the relatively high induced RF voltages
that arise across the antenna. Higher induced RF voltages across
the ICP source antenna can increase the risk of capacitive coupling
and raising the plasma potential.
[0004] One advantage of ICP over conventional parallel plate plasma
is its ability to control the plasma density and ion energy (for
the ion flux arriving at the substrate in process) independent of
each other. The plasma density is primarily controlled by the
applied RF current or power delivered to the ICP source antenna,
whereas the mean ion energy control is performed by an applied RF
bias to the substrate or wafer. The substrate may be a
semiconductor wafer (e.g., silicon), a data storage substrate
(AlSiMag or AlTiC), a photovoltaic substrate (e.g., polysilicon or
silicon), or a flat-panel display substrate (e.g., glass).
[0005] Various types of ICP source designs have been proposed in
prior art. These include spiral coil antenna designs, helicon wall
source designs, and cylindrical coil antenna source designs.
However, all the prior art ICP designs share a common constraint or
limitation which makes them unable to control or adjust the plasma
uniformity profile in real time. The prior art ICP sources are
primarily based on single-zone designs and employ single-coil
antenna structures with a single RF plasma excitation source. The
basic prior art designs mostly employ either a cylindrical or
cone-shaped coil around a quartz chamber (such as a quartz bell
jar) to generate a large-volume plasma or a planar spiral coil
above a dielectric plate (outside the vacuum chamber) to generate a
so-called planar plasma. The spiral coil ICP design often uses a
flat spiral coil, but provides the options to contour the surface
topography of the ICP antenna dielectric housing and/or the antenna
coil itself for improved plasma uniformity.
[0006] The spiral coil design possesses certain technical
advantages, but also has serious limitations. The spiral coil
design allows placement of the antenna above a vacuum dielectric
plate on the atmospheric side or within the vacuum chamber using an
epoxy encapsulation. One can provide a capability to reduce the
induced RF voltage across the spiral coil by placing a few
capacitors in series with the spiral coil loops. This is not a
trivial implementation task since the antenna coil is usually made
of water-cooled aluminum or copper tubing. Insertion of the series
capacitors may require breaking the tubing water flow by insertion
of an in-line metal-to-ceramic insert. Unfortunately, this results
in added structural complexity and increased equipment cost. The
ICP sources with cylindrical coils around the electrically
insulating plasma source or process chamber require an electrically
insulating process chamber or plasma source wall material such as
quartz tube or aluminum oxide tube used in some source designs such
as the helicon plasma sources. These bulk ICP sources can suffer
from plasma non-uniformity problems and usually require a
multipolar magnetic bucket inserted between the plasma source
chamber and the process environment to generate an expanded uniform
plasma. This, however, results in reduced processing throughput due
to reduced plasma density and ion flux density at the substrate.
Moreover, these sources may generate contaminants and particulates
due to sputtering of the plasma source chamber wall material near
the excitation RF antenna.
[0007] The ICP coil is usually driven by a 13.56 MHZ RF source. The
RF current also induces an RF voltage across the antenna coil. In
order to eliminate any electric field induced arcing or chamber
sputtering, the amount of induced RF voltage must be minimized.
This condition places a limit on the maximum allowable excitation
coil inductance or the number of coil turns. Moreover, for a given
coil design (e.g., a given number of turns or inductance) there is
an upper limit on the maximum allowable RF source frequency. In
addition, for a given conventional ICP source design and a
specified excitation RF frequency (e.g., 13.56 MHZ), there is a
limit on the maximum allowable RF power delivered to the ICP
antenna in order to ensure minimal chamber or plasma source wall
sputtering and reduced process contamination. The prior art designs
for ICP coils, therefore, mostly suffer from plasma process
nonuniformity problems, are not easily scalable for larger wafer
processing, and have a relatively narrow useful process window (in
terms of RF power, pressure, etc.). The conventional ICP designs do
not provide any direct method of real-time plasma uniformity
control without compromising the significant process state or
substrate state parameters.
[0008] Advanced plasma fabrication processes require excellent
plasma density and ion flux uniformity control over the entire
wafer surface. Plasma uniformity requirements in high-density
plasma sources are dictated by both process uniformity requirements
and device damage considerations. Typically, the plasma
nonuniformity must be less than 5% (3-sigma value) to ensure
damage-free uniform processing. Many conventional ICP source
designs fail to meet these stringent process uniformity
requirements for various plasma processing applications.
SUMMARY OF THE INVENTION
[0009] In accordance with the present invention, a method and
system for creating an inductively-coupled plasma (ICP) environment
for various device fabrication applications is provided that
substantially eliminates or reduces disadvantages and problems
associated with previously developed ICP processing methods and
systems. The ICP processing method and system of this invention is
applicable to manufacturing of semiconductor, data storage,
flat-panel display, and photovoltaic devices.
[0010] According to one aspect of the invention, there is provided
a multi-zone high-density inductively-coupled plasma source
structure and method of use that includes a first individually
controlled inductive coil for producing a first plasma zone from a
process gas. A second individually controlled coil is included in
the ICP source for producing a second plasma zone from a process
gas. In various embodiments, more than two individually controlled
inductive coils may be used. In one embodiment, a separate RF power
supply may be used for each ICP coil zone. Each ICP coil zone may
be made of either a single coil segment or a set of coil segments
interconnected using at least one series capacitor.
[0011] Another aspect of the present invention is a
hermetically-sealed ICP source structure and fabrication method
that are applicable to both the multi-zone ICP structure of the
present invention as well as the in-situ monitoring sensors; (7)
improved manufacturing equipment cleanliness for enhanced device
manufacturing yield; (8) increased plasma process throughput; and
(9) improved plasma equipment reliability and process
repeatability/performance due to improved ICP source integrity.
[0012] The multi-zone ICP source design is applicable to
manufacturing of semiconductor devices, data storage devices,
photovoltaic devices, and flat-panel displays. Selection of the
number of ICP zones depends on several parameters and
considerations including ICP source diameter, substrate size,
source design type, maximum total RF power, and plasma process
throughput requirements. For most of the practical applications
semiconductor processing, the number of the ICP source zones may be
two to four, however, greater number of zones may be desirable for
different applications such as those for very large-area substrate
processing. For instance, a two-zone ICP source (antenna) design
may be used to adjust the relative edge-to-center plasma process
uniformity in a plasma equipment used for processing of 150-mm or
200-mm semiconductor wafers. An ICP source design with two to five
excitation zones may be used for processing of 200-mm and 300-mm
silicon wafers.
[0013] A technical advantage of the present invention therefore, is
that it provides multi-zone high-density plasma source structure
using at least two individually controlled coil segments for
uniform plasma processing. The multi-zone ICP source structure of
this invention may be constructed either using the more
conventional ICP source fabrication and assembly methods (i.e., at
least two cooled or temperature-controlled coils placed either
outside the process chamber adjacent to a dielectric vacuum plate
or encapsulated in an electrically insulating housing inside the
ICP vacuum process chamber), or using a hermetically-sealed antenna
structure placed within the vacuum environment.
[0014] Another technical advantage of the present invention is that
is provides a hermetically-sealed ICP source fabrication structure
and method that are applicable to both the conventional single-zone
ICP structures as well as the multi-zone ICP source structure of
this invention. This novel method and structure eliminates the need
for elastomer O-ring seals and separate ICP antenna epoxy
encapsulation by providing a high-integrity ICP source structure
compatible with the ultrahigh vacuum (UHV) base pressure
requirement of 5.times.10.sup.-9 Torr or less.
[0015] Yet a further technical advantage of the present embodiment
is an in-situ sensor view port design which can be used for
implementation of some useful plasma state and wafer state sensors
such as full-wafer interferometry sensor and a spatially resolved
optical emission sensor. The full-wafer-view optical port uses a
hermetically sealed optical (e.g., sapphire or quartz) window or
plug located at the center of the ICP source. This port enables
real-time (or run-by-run) plasma process uniformity control using
the multi-zone ICP source design of this invention in conjunction
with a process uniformity monitoring sensor (such as a full-wafer
interferometry sensor).
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] For a more complete understanding of the present invention
and the advantages thereof, reference is now made to the following
description which is to be taken in conjunction with the
accompanying drawings in which like reference numerals indicate
like features and wherein:
[0017] FIG. 1 shows a cross-sectional view of a first embodiment of
the multi-zone ICP source of present invention configured as a
two-zone ICP source;
[0018] FIG. 2 provides a view of the two-zone inductively-coupled
plasma antenna portion embedded in the middle ceramic ICP or
dielectric plate for the FIG. 1 embodiment (first embodiment);
[0019] FIG. 3 shows a cross-sectional view of the top ceramic or
dielectric plate of the FIG. 1 embodiment (first embodiment);
[0020] FIG. 4 illustrates the bottom view of the middle dielectric
plate indicating the gas dispersion cavities and their associated
gas injection inlets for the multi-zone ICP embodiment of FIG. 1
(the first embodiment);
[0021] FIG. 5 depicts a first cross-sectional view of an
alternative or second embodiment of multi-zone ICP structure of the
present invention;
[0022] FIG. 6 shows a second cross-sectional view of the FIG. 5
embodiment (second embodiment) of the invention;
[0023] FIG. 7 provides a cross-sectional view of the middle
dielectric plate of the FIG. 5 embodiment (second embodiment);
[0024] FIG. 8 illustrates the hermetically-sealed coil structure of
the FIG. 5 embodiment of the invention or the top view of the
middle dielectric plate of the second embodiment;
[0025] FIG. 9 depicts a top facial view of the top vacuum plate of
the FIG. 5 embodiment, indicating the feedthroughs for electrical
RF, gas injection, and cooling water;
[0026] FIG. 10 shows a cross-sectional view of a modified version
of the second multi-zone ICP embodiment where the distance between
the vacuum plate and the ICP housing has been increased in order to
enable smaller minimum ICP source to substrate spacing for enhanced
ICP process throughput rate;
[0027] FIG. 11 shows a second cross-sectional view of the modified
version of the second ICP embodiment of FIG. 10 mounted on a vacuum
process chamber for high-throughput plasma-assisted processing
applications;
[0028] FIG. 12 shows a first cross-sectional view of another
(third) embodiment of the invention;
[0029] FIG. 13 includes a second cross-sectional view of the FIG.
12 embodiment (third embodiment);
[0030] FIG. 14 provides a cross-sectional view of the middle
dielectric plate of the FIG. 12 embodiment (third embodiment);
[0031] FIG. 15 is a first cross-sectional view of yet another
embodiment of the present invention (fourth embodiment);
[0032] FIG. 16 provides a second cross-sectional view of the FIG.
15 embodiment of the invention (fourth embodiment);
[0033] FIG. 17 illustrates a top view of the vacuum plate of the
FIG. 15 embodiment (fourth embodiment), indicating various
feedthroughs for process gas inlets, coolant flow, and electrical
connections;
[0034] FIG. 18 shows a bottom view of the vacuum plate appearing in
FIG. 17, indicating the radial low-reluctance magnetic rod
positions;
[0035] FIG. 19 depicts a cross-sectional view of the bottom
dielectric plate for the FIG. 15 embodiment of the invention
(fourth embodiment);
[0036] FIG. 20 is a top view of the bottom dielectric plate of FIG.
19;
[0037] FIG. 21 provides a bottom facial view of the top dielectric
plate of the FIG. 15 embodiment of the present invention (fourth
embodiment);
[0038] FIG. 22 shows the overall schematic view of a vacuum process
chamber using the multi-zone ICP source structures of this
invention (example shows a three-zone ICP configuration);
[0039] FIG. 23 illustrates the schematic diagram of a two-manifold
gas distribution arrangement for the ICP source of FIG. 17 where
the input gases are partitioned into two groups;
[0040] FIG. 24A shows a schematic electrical wiring diagram of a
three-zone ICP configuration for the multi-zone ICP source of FIG.
17;
[0041] FIG. 24B shows a schematic electrical wiring diagram of a
two-zone ICP configuration for the multi-zone ICP source of FIG.
17;
[0042] FIG. 25A shows a schematic electrical wiring diagram of a
three-zone ICP configuration for a single RF power supply based on
an adjustable capacitor array; and
[0043] FIG. 25B shows a schematic electrical wiring diagram of a
three-zone ICP configuration for a single RF power supply based on
an adjustable air-core transformer.
DETAILED DESCRIPTION OF THE INVENTION
[0044] Preferred embodiments of the present invention are
illustrated in the FIGUREs like numerals being used to refer to
like and corresponding parts of the various drawings.
[0045] The embodiment of the present invention that FIGS. 1 through
4 describe is a hermetically-sealed multi-zone (HMZ) ICP source for
various high-density plasma applications, including plasma etch,
PECVD, surface cleaning, plasma hydrogenation, and other
plasma-assisted, fabrication processes. The concepts of the present
invention apply not only to a two-zone ICP source, but also to a
multi-zone source with any number of ICP excitation zones (2, 3, 4,
and more). Moreover, the preferred embodiment of this invention is
for implementation of the HMZ ICP source inside the ICP vacuum
process chamber in order to eliminate the need for a dielectric
vacuum window and to enable implementation of an all-metal-seal ICP
source and process chamber for improved vacuum integrity by
reducing the chamber vacuum base pressure. It is, however,
understood that the HMZ ICP source of this invention can also be
implemented outside the vacuum chamber using a dielectric vacuum
window for separating the source from the process chamber.
[0046] The HMZ ICP source of FIGS. 1 through 4 provides a design in
conjunction with a six-zone showerhead gas injector. The HMZ ICP
source, however, is also compatible with the use of either a
single-zone showerhead or a multi-zone showerhead with any number
of independently controlled showerhead zones (e.g., from one to ten
zones). Some applications such as surface cleaning may require only
a single-zone showerhead while other applications such as PECVD may
benefit from using multiple showerhead zones for improved process
uniformity control via multi-zone gas flow adjustment. The
multi-zone showerhead feature allows radial control of the process
gas mass transport profile which is particularly useful for uniform
PECVD applications. Moreover, using the multi-zone showerhead, the
source can be used for injection of multiple gases without
premixing the gases. As a result, mixing of multiple gases occurs
in the plasma process environment and not inside the delivery gas
lines or inside the ICP source. Separation of multiple process
gases, such as in a binary gas system in CVD applications, can
eliminate the possibility of gas phase nucleation and particulate
generation inside the showerhead. For instance, in a PECVD process
used for silicon dioxide deposition, the process gas system may
comprise SiH.sub.4 and N.sub.2O. Using the multi-zone showerhead
arrangement of this invention, these gases can be separated and
injected as a binary system into alternating adjacent showerhead
zones.
[0047] With this introduction, more particular attention is now
drawn to FIG. 1. FIG. 1 shows HMZ ICP source 100 that includes
water-cooled or temperature-controlled metallic top vacuum plate
102, which may be formed of stainless steel or aluminum, that
adjoins top dielectric plate 104. Top dielectric plate 104 is
hermetically sealed or bonded to middle dielectric plate 106 which
itself hermetically bonds to showerhead injector plate 108. Optical
plug (or window) 110 passes through metallic top plate 102, top
dielectric plate 104, middle dielectric plate 106, and showerhead
injector plate 108, and provides an optical viewport to the entire
wafer surface throughout the fabrication process. The optical
viewport can also be used for monitoring of the plasma process
parameters using a suitable optical sensor, such as spatially
resolved plasma emission sensor.
[0048] Metallic top plate 102 includes numerous feedthroughs or
penetrations, some of which are for coolant (e.g., water) flow
purposes, some are for ICP gas injections, and the remaining ones
are for electrical RF feedthroughs. For example, the first set of
showerhead gas inlets 112, 114, and 116 pass through metallic top
plate 102, are bonded to the holes within the top dielectric plate
104, and feed into the holes within the middle dielectric plate 106
in order to inject the process gases into respective showerhead
zone dispersion cavities 118, 120, and 122. Showerhead zone
cavities 118, 120, and 122 direct process gases to the rings of
injection holes 124, 126, and 128 of showerhead injector plate 108.
Likewise, showerhead inlets 130, 132, and 134 also pass through
metallic top plate 102, are bonded to holes within the top
dielectric plate 104, and feed into the holes within the middle
dielectric plate 106 in order to inject the process gases into
respective showerhead zone dispersion cavities 136, 138, and 140.
From the associated showerhead zone cavities 136, 138, and 140,
plasma process gases pass through and out of several rings of gas
injection holes 142, 144, and 146 of showerhead injector plate
108.
[0049] Also penetrating through vacuum base plate 102 are a
plurality of electrical RF feedthroughs including RF feedthroughs
150 and 152. RF feedthrough 150, for example, connects through RF
feedthrough connection 154, passes through channel 156 of metallic
top plate 102, continues through top dielectric plate 104, and
continues into cooling water channel 160 of middle dielectric plate
106 until it contacts ICP antenna RF coil segment 173 (which is
part of a two-zone HMZ ICP source 100 arrangement).
[0050] Hermetically-sealed ICP source 100 includes two zones of
cooling (such as water cooling) to remove heat generated by the
ohmic power losses due to RF power delivery and ICP plasma
generation process. The first zone includes inlet channel 162 that
passes through metallic top plate 102 and is bonded to the top
dielectric plate 104 for providing cooling water to cooling water
channel 164 of middle dielectric plate 106. Middle dielectric plate
106 provides internally a cooling path by which water may enter,
for example, cooling channel 164, pass through to cooling channels
160 and ultimately enter cooling channel 166. From cooling channel
166, cooling water exits from the ICP source through outlet 168.
Outlet 168 receives the cooling water from the zone 1 cooling
channels and permits continuous flow of cooling water from cooling
water inlet 162 through cooling channels 164, 160, and 166 with a
continuous heat removal action. In the first zone of
hermetically-sealed ICP source 100, zone-1 RF contact 170 provides
a path by which an RF current may flow through each of plated (or
molded or inserted) coil segments 172, 173, and 174 of zone-1.
[0051] In completing the description of hermetically-sealed ICP
source 100 as depicted in FIG. 1, in metallic top plate 102 are
cooling channel feedthroughs for receiving cooling water including
cooling channel 176 connected to zone-1 inlet channel 162 (via an
in-line insulating ceramic tube insert), and cooling channel 178
connected to zone-1 outlet channel 168 (via an in-line insulating
ceramic tube insert for electrical isolation). Cooling water inlet
180 connects to in-line insulating ceramic tube insert 182 for
providing cooling water to cooling channel 184 of zone-2 of
hermetically-sealed ICP source 100 and its surrounding region. In
middle dielectric plate 106, coolant passes to cooling water
channel 188 for cooling coil segment 190 and its surrounding
region. From cooling channel 188, cooling water flows in middle
dielectric plate 106 to cooling channel 192 for cooling coil
segment 194 of zone-2 of the hermetically-sealed ICP source and its
surrounding region. The cooling water subsequently flows out of the
zone-2 coils via coolant outline 197.
[0052] In middle dielectric plate 106, cooling water channels 164,
160, 166, 184, 188, and 192 have been shown with progressively
greater depths. This configuration enables vertical contouring of
respective coil segments 174, 173, 172, 186, 190, and 194. This ICP
antenna contouring (convex or concave contouring) provide an
additional design parameter to optimize the ICP uniformity
performance. Showerhead 108 is made of an electrically insulating
and thermally conductive material, preferably formed of a ceramic
material such as aluminum nitride (AlN), aluminum oxide
(Al.sub.2O.sub.3), or boron nitride (BN). Similarly, the top and
middle dielectric plates 104 and 106 should be made of a suitable
electrically insulating and thermally conducting material such as
AlN, Al.sub.2O.sub.3, or BN. As appropriate, the contacting
interfaces between the plates of hermetically-sealed ICP source 100
are hermetically bonded or fused (preferably using a thermal
bonding process) or otherwise connected (such as with a
high-temperature cured UHV-compatible epoxy) in order to establish
a sealed ICP antenna encapsulation housing for ultraclean plasma
processing. For example, metallic top vacuum plate 102 and top
dielectric plate 104 are fused or hermetically bonded together
using a thermal bonding (e.g. with indium) or epoxy bonding
process. Top dielectric plate 104 and middle dielectric plate 106
are also bonded together at their contact interface junctions.
Similarly, middle dielectric plate 106 and showerhead injector
plate 108 are also bonded together at their contact junctions. All
four plates (metallic plate 102 and ceramic plates 104, 106, and
108) can be bonded together using a single thermal bonding process
using indium or another suitable bonding or brazing material.
[0053] Optical plug 110 provides a viewpoint for probing or viewing
the plasma process environment. On top of optical plug 110 is view
port 198 which is connected or sealed (using a metal or wire seal)
to metallic top plate 102 through hermetically sealed flange 200.
The hermetically-sealed ICP source employs a water-cooled (or
gas-cooled) metallic (stainless steel) top vacuum plate 102 to
support the ICP source inside the plasma process chamber and to
enable establishing a UHV base pressure of less than
1.times.10.sup.-8 Torr. Metallic top plate 102 also provides all
the necessary feedthroughs (RF, gas inlets, and cooling water
inlets/outlets for the ICP coil channels), and provides a vacuum
seal (e.g., using a metal seal) to the ICP process chamber. The
metallic top vacuum plate 102 cooling may be performed either
indirectly using the ICP source coolant (water) flowing through the
coil channels in the ceramic housing, or directly using separate
embedded cooling channels inside the metallic vacuum top plate 102
itself.
[0054] Hermetically-sealed ICP source 100 of the FIG. 1 embodiment,
therefore, consists of two RF power sources (for a 2-zone ICP
arrangement), 12 electrical RF feedthroughs for 6 coil segments and
six pairs of electrical contacts, four coolant feedthroughs
(including two inlets and two outlets), and six process gas inlets
(assuming six injection zones). However, for the same two-zone ICP
coil configuration of hermetically-sealed ICP source 100, the
number of external coolant feedthroughs can be reduced to two by
connecting the zone-1 and zone-2 water channels in series within
the ICP ceramic housing middle dielectric plate.
[0055] FIG. 2 shows a top view of the middle dielectric or ceramic
insulator plate comprising the two-zone antenna configuration for
ICP antenna 202 of the present embodiment. Multi-zone ICP antenna
202 is fabricated within middle dielectric plate 106 of
hermetically-sealed ICP source 100. Middle dielectric plate 106 is
made of a thermally conductive and electrically insulating material
such as AlN, Al.sub.2O.sub.3, or BN. Formed in ICP source middle
dielectric plate 106 are two RF antenna zones for ICP generation
that are conceptually differentiated by dash line 206. For example,
that portion of ICP antenna 202 outside of dash line 106
corresponding to the antenna segments 172, 173, and 174 forms the
zone-1 antenna 208, while that portion within dash line 206
containing the antenna segments 186, 190, and 194 forms the zone-2
antenna 210.
[0056] As FIG. 2 further indicates, at the center of zone-2 antenna
210 appears the feedthrough hole for optical viewport plug 110.
Zone-1 or outer zone antenna 208 begins with outer zone-1 RF
contact 211 that connects to plated (or a combination of sputtered
and plated, or inserted broken ring) coil segment 172 that was
originally introduced in FIG. 1. The coil segment 172 is formed in
a circular path as a broken ring and continues to RF terminal
contact 212. The coolant groove 164 over outer zone coil segment
172 is connected in series to the adjacent outer zone coils segment
173 coolant channel 160 via jumper water channel 214 of middle
dielectric plate 106. Connecting to unplated (electrically
insulating) jumper water channel 214 is RF terminal contact 150
(FIG. 1) which also connects to ICP coil segment 173. ICP coil
segment 173 is also formed as a broken ring and takes a circular
path around middle dielectric plate 106 to connect to RF terminal
contact 216. The coolant groove 160 of the outer zone segment 173
is connected in series to the coolant groove channel 166 of the
outer zone segment 174 via unplated or conductor-free coolant
channel 218 between the RF contacts 216 and 220. The RF terminal
contact 220 connects to outer zone plated (or conductor covered)
coil segment 174 that takes a broken ring circular path to outer
zone RF contact 170.
[0057] The inner zone or zone-2 antenna 210 begins at RF contact
222 which connects to inner zone coil segment 186. Coil segment 186
runs in a circular pattern as a broken ring and connects to RF
terminal contacts 222 and 224. The coolant groove channel 184 of
the inner zone coil segment 186 connects to the inner zone adjacent
coil segment coolant groove channel 188 via unplated (conductor
free or electrically insulating) coolant channel jumper 226. The
inner zone coil segment 190 runs as a broken ring (using plated or
inserted conductor) underneath coolant groove channel 188 between
RF contacts 227 and 228. The coolant groove channel 188 of the
inner zone coil segment 190 connects to the inner zone coolant
groove channel 192 of the coil segment 194 via unplated (conductor
free or electrically insulating) coolant channel 230. The RF
contacts 224 and 227 are externally connected together via an RF
capacitor. Similarly, the RF contacts 228 and 232 are linked
together via another external RF capacitor. These external
capacitor connections (on the atmospheric side of the ICP source)
create a 3-turn inner zone coil with two series capacitors for
reduced induced voltage. The inner zone RF power supply contacts
are the RF contacts 222 and 234. The RF contact 234 connects to
coil segment 194 which surrounds optical viewport plug 110 as a
broken ring and connects to inner zone RF contact 232. As can be
seen in ICP antenna 202, zone-2 antenna portion 208 may operate
independently of zone-1 antenna 210 using two separate RF power
supplies.
[0058] The hermetically-sealed ICP source 100 antenna 202 of FIG.
2, therefore, contains two inductive antenna zones each with three
turns. The same design may be arranged with a different external
wiring configuration in order to establish, for instance, a
three-zone ICP source with two coil turns in each zone. Although a
three-zone ICP configuration or another design with more zones is
well within the scope of the present invention, the remainder of
this description focuses on a two-zone ICP source design
configuration. It should be also noted that the design of FIGS. 1
through 4 is electrically configurable externally without any
hardware design modifications within the ICP source structure.
[0059] As FIG. 2 shows, six pairs of electrical RF contacts are
made to the six coil turns using ultrahigh vacuum (UHV) compatible
electrical RF feedthroughs in metallic top plate 102 and
spring-loaded (or soldered) electrical wires attached to the coil
segments. These 12 electrical contacts connect to the multi-zone
segment terminals 211 (Z.sub.11), 212 (Z.sub.12), 150 (Z.sub.13),
216 (Z.sub.14), 220 (Z.sub.15), 170 (Z.sub.16), 222 (Z.sub.21), 224
(Z.sub.22), 227, (Z.sub.23), 228 (Z.sub.24), 232 (Z.sub.25), and
234 (Z.sub.26). For a two-zone hermetically-sealed ICP source 100
configuration with three coil turns in each zone, the external
electrical wiring and capacitor connections is as follows: The
electrical RF terminal contacts 211 (Z.sub.11) and 170 (Z.sub.16)
connect to the first zone RF (e.g., 13.56 MHZ) power supply.
External capacitor terminal contacts 212 (Z.sub.12) and 150
(Z.sub.13) connect via an external RF capacitor. External capacitor
terminal contacts 216 (Z.sub.14) and 170 (Z.sub.15) connect via a
second RF capacitor. This completes the formation of ICP zone-1
antenna 208 comprising three coil turns and two external capacitors
in series. ICP zone-2 antenna 210 is configured by connecting the
electrical RF terminal contacts 222 (Z.sub.21) and 234 (Z.sub.26)
to the second RF power supply. One external RF capacitor is used to
connect RF terminal contacts 224 (Z.sub.22) and 227 (Z.sub.23)
while another RF capacitor links RF terminal contacts 228
(Z.sub.24) and 232 (Z.sub.25) together. A phase shifter/controller
may be used between the two ICP RF power supplies in order to
control the phase angle between the two power sources. Moreover,
another phase shifter may be used to control the phase angle
between any of the ICP RF sources and the substrate bias RF power
supply. If desired, the ICP source 100 design of FIGS. 1 through 4
may be externally configured for operation as an n-zone ICP source
with n=1, 2, 3, 4, or even larger. The number of coil turns in each
zone can also be selected by the design of the external wiring and
series RF capacitor arrangement.
[0060] FIG. 3 describes in more detail the construction of top
dielectric plate 104 including the bonded ICP feedthroughs. Top
dielectric plate 104 may be formed of a thermally conductive and
electrically insulating ceramic material such as aluminum nitride
(AlN), boron nitride, or even aluminum oxide. Top dielectric plate
104 has, in the present embodiment, several bonded feedthroughs for
two antenna zones and six showerhead zones. In the left-hand side
feedthrough section 240, ICP antenna zone-1 electrical feedthrough
150 connects to one of the RF contacts in zone-1 RF antenna 208 of
FIG. 2. There are six electrical RF feedthroughs for the ICP zone-1
segments and another six electrical RF feedthroughs for the ICP
zone-2 segments. In the right-hand side feedthrough section 242,
ICP antenna zone-2 electrical feedthrough 152 connects to one of
the RF contacts in zone-2 RF antenna 210 of FIG. 2. Top dielectric
plate 104 also includes the necessary feedthrough inlets 112, 114,
116, 130, 132, and 134 for gas flow connections to the showerhead
injector dispersion cavities (six showerhead zones are shown).
Similarly, top dielectric plate 104 permits flow of cooling water
through bonded tubes for zone-1 coolant inlet 162 and zone-1
coolant outlet 168. Top dielectric plate 104 also includes two
bonded tubes for zone-2 coolant inlet 180 and zone-2 coolant outlet
197. Except for the RF feedthroughs, all the bonded feedthroughs
(gas injection inlets and coolant inlet/outlet tubes) are flushed
against the bottom surface of the top dielectric plate 104 (or they
can be bonded to the dielectric holes by partial feeding the tubes
into a fraction of the dielectric plate thickness).
[0061] FIG. 3, therefore, illustrates top dielectric plate 104 with
all the bonded tubings (for gas injection and water cooling) and
electrical RF connectors. For an ICP source with a multi-zone
injector, multiple gas injection tubes are used whereas for an ICP
source with a single-zone showerhead, a single gas injection tube
can be used. The FIG. 3 design also shows four water cooling tubes
162, 168, 180, and 197. If desired, the number of water cooling
feedthrough tubes can be reduced to two by interconnecting the ICP
antenna cooling channels in series internally by added coolant
groove segments (w/o metallization or conductor jumpers/links)
between the broken rings in the middle dielectric plate containing
the ICP antenna grooves containing the conductor grooves.
[0062] FIG. 4 illustrates a facial bottom surface view of the
middle dielectric plate 106 of the present embodiment. This
dielectric plate surrounds optical plug 110 and may be formed of a
thermally conductive and electrically insulating ceramic material
such as aluminum nitride (AlN), boron nitride (BN), or even
aluminum oxide (Al.sub.2O.sub.3). In the present embodiment,
ceramic showerhead 108 includes six gas injection zones, each
corresponding to one of the gas dispersion cavities embedded in the
middle dielectric plate 108 and shown in FIG. 4. These gas
dispersion cavities are shallow circular grooves formed in the
middle dielectric plate 106 and connected to the gas injection
inlets. In particular, inner gas dispersion cavity ring 140
receives process gas via gas injection inlet 134 and uniformly
directs the process gas to the inner zone of showerhead 108
injection holes 146. Second gas dispersion cavity 138 receives
process gas via gas injection inlet 132 and uniformly distributes
the process gas to the second zone of showerhead injection holes
144. Third gas dispersion cavity 136 receives process gas from gas
injection inlet 130 and distributes the process gas to the third
zone of showerhead injection holes 142. Fourth gas dispersion
cavity 122 receives process gas through inlet 116 and guides the
process gas to the fourth zone of showerhead injection holes 128.
Fifth gas dispersion groove 120 receives process gas from inlet 114
and distributes the process gas to the fifth zone of showerhead
injection holes 126. Sixth gas dispersion cavity 118 receives
process gas from inlet 112 and directs the process gas to the outer
zone of showerhead injection holes 124.
[0063] The vacuum, water, and process gas seals for
hermetically-sealed ICP source 100 may be established either using
bonded junctions that are formed using a thermal bonding process
or, alternatively, elastomer O-ring seals. Thermal bonding using a
suitable low melting point metal or metal alloy is a preferred
method for establishing hermetic seals in ICP source 100 since a
bonded structure eliminates the possibilities of process
contamination, base pressure degradation, and outgassing problems
associated with elastomer O-ring seals. Indium, indium alloys, or
other suitable bonding materials may be used for formation of the
bonded ICP structure. An alternative to metal-based thermal bonding
is hermetic bonding using a thermally cured epoxy material.
[0064] As shown in FIG. 1, besides the metallic top plate 102, ICP
source 100 housing comprises a stack of three electrically
insulating disks. As described earlier, these disks may be made of
a ceramic material, preferably a thermally conductive ceramic
material such as aluminum nitride (AlN), boron nitride (BN),
alumina (Al.sub.2O.sub.3), or even a plasma-resistant polymer based
material, such as Vespel. Due to their high-temperature stability,
ceramic materials work well for the ICP source 100 structure when
assembled using a thermal bonding process. This is due to the fact
that the thermal bonding processes using various bonding materials
may require bonding temperatures in the range of 200.degree. C. to
600.degree. C. A bonding temperature of <300.degree. C. can be
used using tin (Sn) or indium (In) or their alloys as the metallic
bonding material. Moreover, the epoxy bonding processes usually
employ thermal cure temperatures <300.degree. C.
[0065] The use of optical viewport 198 of ICP source 100 is
optional and this viewpoint may be positioned at the center of
hermetically-sealed ICP source 100. Optical plug or light pipe 110
may be made of a suitable optically transmissive light pipe
material such as quartz or sapphire for implementation of a
real-time in situ sensor. Viewport 198 provides a suitable wafer
view for integration of a full-wafer interferometry sensor for
real-time rate and process uniformity control. This viewport can
also be used for integration of other types of plasma sensors such
as a single-wavelength or spectral plasma emission sensor. The ICP
source design concepts of this invention are applicable to both
planar and contoured ICP coil designs. For 8" wafer processing,
metallic top plate 102 may have a diameter of 14" to 20". The
vacuum plate diameter could be as much as 20" as is the case of the
Universal Plasma Module (UPM) manufactured by CVC Products of
Rochester, New York, which has an internal chamber diameter of 18".
Metallic top plate 102 may have thickness in the range of 1/4" to
1" to provide sufficient mechanical strength for use on a vacuum
process chamber.
[0066] Top dielectric plate 104, middle dielectric plate 106, and
showerhead 108 form a stack of three bonded ceramic (AlN,
Al.sub.2O.sub.3 or BN) or polymer-based (e.g., Vespel) disks as the
main ICP antenna housing of the ICP source 100. The showerhead
plate 108 is a relatively thin plate (e.g., a thickness of 1/8" to
1/4") with an array of rings of circular holes (0.5 mm to 1 mm
diameter holes) forming a six-zone showerhead configuration. The
central opening 109 of showerhead 108 preferably has a diameter in
the range of 0.50" to 1.5" to receive viewport optical plug 110.
Showerhead 108 is thermally bonded (or connected using an elastomer
O-ring seal) to the middle dielectric plate 106 which contains the
ICP RF antenna coil segments and cooling water channels.
[0067] The ICP source embodiment depicted in FIGS. 1 through 4
shows that only the bottom surface of the ICP antenna grooves or
the coolant channels contain conductor channels to form the ICP
coil segments. If desired, a metallization process (e.g.,
electrochemical plating or a combination of sputtering and
electroplating depositions) may be used to form the conductor
channels by coating not only the cooling channel bottom surfaces,
but also the groove sidewalls for reduced RF resistance. For 8",
wafer processing, the optimum ICP source ceramic housing diameter
is 10" to 14" and preferably 12". If desired, the ICP antenna
conductor segments may be prefabricated from a suitable material
such as aluminum or copper and subsequently inserted in the
designated antenna channels.
[0068] FIG. 5 shows a first cross-sectioned view of an alternative
or second embodiment of the present invention as ICP source 300.
This alternative embodiment demonstrated in FIGS. 5 through 9 shows
a planar hermetically-sealed multi-zone (HMZ) ICP source design
without any contouring of the ICP antenna or the dielectric
housing. HMZ ICP source 300 includes metallic (e.g., stainless
steel) vacuum plate 302 that attaches to top dielectric plate 304
and provides vacuum seal to plasma process chamber (not shown). Top
dielectric plate 304 contacts vacuum plate 302 either using
hermetic bonded junctions or elastomer O-ring seals (301 and 303).
Top dielectric plate 304 attaches to middle dielectric plate 306
via junctions 305 and 307 which are formed either using hermetic
bonding or O-ring seals. Moreover, middle dielectric plate 304 is
sealed against showerhead plate 308 using bonded junctions 309 or a
single outer O-ring seal. Optical viewport 310 includes optical
plug 110 or optical window 198 which is hermetically sealed to
flange 200 which is secured to vacuum plate 302 using a metal or
wire seal. In addition, vacuum plate 302 includes numerous embedded
coolant channels to prevent heating of the plate 302 by the ICP RF
antenna. Multi-zone process gas injection inlets 314 pass through
feedthrough holes 312 in vacuum plate 302, pass through top
dielectric plate 304, and continue to middle dielectric plate 306
to provide process gas to showerhead zone dispersion cavities 316.
Showerhead zone dispersion cavities 316 receive process gases from
the showerhead inlets 314 and provide uniform gas distribution to
showerhead injection hole, 318.
[0069] Besides the gas dispersion cavities 316 and bonded gas
injection inlets 314, the lower dielectric plate 306 also includes
the ICP source antenna segments 328 (eight separate segments
shown). The ICP source antenna segments 328 are formed by filling
the grooves formed on the top surface of the middle dielectric plat
using a plating, evaporation, sputtering, or a casting/molding
process. An alternative method is to prefabricate the ICP source
antenna segments from a suitable material such as aluminum or
copper and subsequently insert them in the middle plate antenna
cavities. The ICP antenna segments 328 may also be made of other
metallic materials such as refractory metals. The top dielectric
plate 304 contains coolant grooves 320 formed over the ICP antenna
coil segments. These coolant channels connect to external coolant
inlet/outlet channels and prevent heating of the ICP source housing
during its operation. The ICP structure of FIG. 5 consists of a
stack of four plates (one metal and three dielectric plates) which
are connected together either using an O-ring-free hermetic bonding
process (using indium or another material as a bonding agent or
using thermal epoxy bonding) or using elastomer O-ring seals. The
dielectric plates may be made of a suitable ceramic (AlN, BN, or
Al.sub.2O.sub.3) or polymer (e.g., Vespel) material. The gas
injection inlets 314 (made of stainless steel tubes) are externally
connected to one or more gas manifolds for single-zone or
multi-zone showerhead operation.
[0070] FIG. 6 shows a different cross-sectional view of multi-zone
ICP source 300 of FIG. 5 along a cross-sectional plane which is
perpendicular to that of FIG. 5. Components previously described in
connection with FIG. 5 are identical to those appearing in FIG. 6.
FIG. 6 shows additionally, however, cooling water (or any coolant)
inlet 321 for directing cooling water to the cooling water channels
320 which are connected in series by coolant jumpers within top
dielectric plate 304 to cooling water outlet 322. To connect
various components of multi-zone ICP source 300, the present
embodiment uses several bonded junctions 324 using indium or
another suitable bonding material. FIG. 6 also shows spring-loaded
or soldered electrical feedthrough connectors 313 for various ICP
antenna coil segments. For instance, sixteen electrical connectors
are used for the ICP source structure with eight (antenna) coil
segments.
[0071] FIG. 7 shows one embodiment of middle dielectric plate 306
that appears in the FIG. 5 embodiment. As previously mentioned,
middle dielectric plate 306 is made of a suitable thermally
conductive and electrically insulating substrate material which
includes passageway 326 for receiving optical plug 110 of optical
viewport 198 (or for providing an optical view of the plasma
chamber and/or wafer surface) for sensor-based process monitoring
and control applications. In a circular broken-ring configuration,
numerous aluminum-filled or copper-filled (or in general electrical
conductor filled) grooves or trenches appear for receiving radio
frequency electrical power and serving as multi-zone ICP antenna
portions 328. Also within middle dielectric plate 306 are multiple
showerhead zone dispersion cavities 316. Plate bonding junctions
324 are formed on the top and bottom surfaces of middle dielectric
plate 306 in order to establish hermetic seals for the multi-zone
ICP structure. Middle dielectric plate 306 may be made of a
thermally-conducting, electrically-insulating ceramic disk such as
a 12" diameter disk of aluminum nitride, aluminum oxide, or boron
nitride. In the embodiment of FIG. 7, conductor-filled (such as
aluminum-filled or copper-filled) trenches 328 take the form of
eight planarized coil turns in the shape of broken rings. The
hermetically-sealed multi-zone ICP antenna segments become an
integral part of the middle dielectric plate 306. These antenna
segments may be separately fabricated and subsequently inserted in
the middle dielectric plate trenches 328 prior to hermetic sealing
or bonding of the multi-zone ICP structure. The showerhead zone
dispersion cavities 316 form continuous concentric rings around
optical plug hole 326 on the bottom surface of the middle
dielectric plate 306. Plate bonding junctions 324 can be formed
within hermetic sealing trenches and form continuous concentric
rings between the adjacent gas dispersion cavities on the bottom
surface and multi-zone ICP antenna segments on the top surface. The
bonding material may be, for example, aluminum, tin, aluminum
silicon, indium, or other compatible materials such as brazing
materials or thermally conductive epoxy materials.
[0072] FIG. 8 shows a facial top surface view of middle ceramic
plate 306 to illustrate the hermetically sealed antenna structure
of the embodiment of FIG. 5. In particular, top planarized surface
330 includes, in the FIG. 8 embodiment, nine concentric and
continuous rings of hermetic bonding joints 324 for forming a
hermetic bond between middle dielectric plate 306 and top
dielectric plate 304. Each hermetic bonding joint 324 preferably
includes a circular shallow groove or trench filled with a suitable
bonding material such as indium. To form the multi-zone coil
configuration of FIG. 8, eight (or any other desired number of)
inductive coil segments 328 are employed which are in the form of
concentric broken rings separated from one another by hermetic
sealing trenches 324. Multi-zone coil segments 328 fill the
designated substrate grooves and may be formed of aluminum or
another electrically conductive material such as copper.
[0073] Although eight coil segments are shown in FIG. 8, fewer or
more number of inductive segments may also be used for a specific
application, depending on the multi-zone ICP uniformity control
requirements and substrate size to be processed. Each segment cross
sectional area may be approximately 0.25 inches to 0.5 inches wide
with a thickness of 0.001 inches to 0.120 inches. Each concentric
broken ring 328 includes two electrical contact terminals 332 and
336 for connecting to an external radio frequency power source or
for external interconnection of the antenna coil segments to each
other via RF capacitors. In one example of the FIG. 8 embodiment,
middle ceramic plate 306 has a 12-inch diameter with a 0.25 inch
thickness for eight-inch wafer processing. The plate may be made of
aluminum nitride (AlN), boron nitride (BN), aluminum oxide
(Al.sub.2O.sub.3), or another suitable material.
[0074] FIG. 9 illustrates a top facial view of metallic vacuum
plate 302 for the FIG. 5 embodiment. Top surface 340 of metallic
top plate 302 shows feedthrough channels 312 that permit passage of
multi-zone showerhead process gas inlets 314. The designations of
showerhead inlets appearing in FIG. 9 are as follows. SH-81 and
SH-82 are two half-zone showerhead gas inlets for the outermost
injection zone holes 318 for showerhead injector plate 308 of FIG.
5. Each successive designation SH-71 and SH-72, SH-61 and SH-62,
SH-51 and SH-52, etc., down to SH-11 and SH-12, indicate half-zone
pairs of showerhead inlets for the associated showerhead injection
zone grooves 318 down to the innermost showerhead injection zone
holes 318 closest to the opening for optical plug 110. For the
particular configuration shown in FIG. 5, the gas injection inlets
(SH-11/SH-12 to SH-81/SH-82) can be externally configured using gas
manifolds such that the multi-zone ICP source showerhead may
operate as an n-zone showerhead with "n" selectable between 1 and
8. In addition to showerhead inlets appearing on top surface 340
there also appears ICP source coolant inlet 322 and ICP source
coolant outlet 321. ICP source coolant inlet 322 provides coolant
(e.g., cooling water) flow to coolant channels 320 of top
dielectric plate 304. Coolant inlet 346 and coolant outlet 348
provide a coolant flow for cooling channels embedded within
metallic vacuum plate 302.
[0075] In FIG. 9, metallic top plate 302 also includes on top
surface 340 external RF capacitor components associated with
partitioned ICP source zones 350, 352 and 354 (example shown for a
three-zone ICP source arrangement). These external RF capacitors
include RF capacitors 356 through 364. In the embodiment of FIG. 9,
three radio frequency circuits, including RF power supply RF.sub.1,
RF power supply RF.sub.2, and RF power supply RF.sub.3 provide RF
electrical power signals to the multi-zone ICP source coils via the
external capacitor circuitry. In particular, RF power supply
RF.sub.1 connects to the outer ICP zone via external RF capacitor
circuit 350. RF power supply RF.sub.2 connects to the middle ICP
zone via external power RF capacitor circuit 352. Also, external RF
capacitor circuit 354 delivers power from RF power supply RF 3 to
the inner ICP zone.
[0076] FIGS. 5 through 9, therefore, demonstrate an alternative
embodiment for hermetically-sealed multi-zone ICP source 300 that
has many features similar to the design described earlier. The
alternative design of FIGS. 5 through 9, however, is a completely
planar hermetically-sealed multi-zone ICP source without any
contouring of the ICP coil segments or the dielectric housing. In
this design, middle dielectric plate 306, which may be made of one
of several dielectric materials such as alumina or aluminum
nitride, contains fully metallized grooves, forming the bonded
multi-zone coil structure shown in FIG. 8. The FIG. 8 embodiment
shows eight coil segments, although any number of segments (e.g.,
two to ten) may be used in the design. The middle dielectric plate
306 also includes bottom gas grooves 316 for gas injection. Bottom
gas grooves 316 can be formed as continuous rings which connect to
the bonded gas injection tubes coming from the metallic top plate
302 feedthroughs.
[0077] In this design, hermetically-sealed multi-zone ICP source
300 with its eight coil segments employs an eight-zone showerhead
308 with sixteen gas inlets 314. Each showerhead 308 zone has two
gas injection inlets 314 (e.g., SH-11 and SH-12 inlets connected to
the showerhead zone 1) for enhanced process uniformity. Each
showerhead 308 zone may, however, use only one gas inlet 314 as
long as the showerhead 308 gas grooves or gas dispersion cavities
316 provide sufficient gas flow conductance for axisymmetric gas
injection through the injector plate holes 318. For a single-zone
showerhead (e.g., when ICP is used for low-pressure surface
preparation/cleaning is applications), only a single gas inlet is
required. This can be accomplished by using a gas manifold which
connects to al the gas inlets SH-11/SH-12 through SH-81/SH-82. A
multi-zone gas inlet configuration, however, provides the
flexibility to configure the gas injection as single-zone or
multi-zone injection by appropriate external plumbing and gas
manifolding.
[0078] For the design shown FIGS. 5 through 9, the multi-zone ICP
source water cooling channels are included in top dielectric plate
304. Top dielectric plate 304 also contains all the ICP antenna
electrical feedthroughs as well as the bonded gas injection inlets
and water cooling inlet/outlet tubes. If the entire multi-zone ICP
source 300 structure is hermetically bonded to the stainless steel
vacuum plate and if the ICP dielectric housing plates (three
plates) are made of a relatively high thermal conductivity material
such as aluminum nitride (AlN) or boron nitride (BN), the cooling
channels and the associated cooling feedthroughs may be eliminated
from the top dielectric plate. This is possible because the ICP
housing can be effectively cooled using the water-cooled stainless
steel vacuum plate. A thermally conductive bonded hermetically
sealed junction between the metallic vacuum plate and the top
dielectric plate will facilitate heat transfer from the ICP antenna
to the water-cooled vacuum plate. As shown in FIG. 9, this
multi-zone ICP source can be externally configured as an n-zone
source with n=1, 2, 3, 4, or even more (up to 8 for this particular
design). The configuration shown in FIG. 9 indicates a three-zone
ICP arrangement with three individually controlled RF power
supplies.
[0079] The external RF capacitors 356 through 364 reduce the
induced reactive voltage, resulting in negligible capacitive
coupling and sputtering of the chamber and ICP source materials. In
the configuration shown in FIG. 9, the eight-segment ICP source has
been externally partitioned and configured as a three-zone plasma
source. The outer three coil segments in conjunction with two
external RF capacitors 356 and 358 form the outer ICP zone 350
(using zone-1 power supply RF.sub.1). The middle three coil
segments have been grouped together in conjunction with another
pair of external RF capacitors 360 and 362 to form the middle or
second ICP source zone 352 and are powered by RF power supply
RF.sub.2. The inner two coil segments are connected in series via
external RF capacitor 364 and form the inner or third ICP zone 354.
The inner zone is powered by the third RF power supply (RF.sub.3).
These three RF (e.g., 13.56 MHZ) power supplies may also use phase
shifters/controllers for enhanced and repeatable process control.
Other external wiring arrangements and multi-zone
partitioning(two-zone, four-zone, etc.) are also possible using the
same ICP source design.
[0080] FIG. 10 shows a cross-sectional view of a modified version
of the second multi-zone ICP embodiment (shown in FIGS. 5 through
9) where the multi-zone ICP source housing has been lowered with
respect to the process chamber vacuum lid or flange by increasing
the spacing between the vacuum plate and the ICP housing (by
inserting a welded cylindrical metallic extension part between the
ICP housing and the vacuum chamber lid). This modified
configuration provides a smaller minimum ICP source to substrate
spacing for enhanced ICP process throughput rate, particularly in
plasma process camber designs where the up/down travel range for
the substrate chuck is restricted. FIG. 11 shows a second
cross-sectional view of the modified version of the second
multi-zone ICP source embodiment of FIG. 10 mounted on a vacuum
process chamber for high-throughput plasma-assisted processing
applications. As shown in FIG. 11, the recessed ICP housing allows
reduced ICP source to substrate spacing for enhanced process
throughput.
[0081] FIGS. 12 through 14 show yet another alternative
hermetically sealed multi-zone ICP source 400 embodiment of the
present invention. This preferred design is essentially similar to
the previous design shown of FIGS. 5 through 9 except for two main
differences. FIG. 12 shows alternative hermetically-sealed
multi-zone ICP source 400 embodiment in cross sectional view 400
including metallic top plate 402 that attaches to top dielectric
plate 404, preferably using a thermal bonding or brazing process.
Top dielectric plate 404 attaches to middle dielectric plate 406.
Middle dielectric plate 406 bonds to gas injector plate 408. Top
vacuum plate 402 includes multiple channels 412 for receiving gas
injection inlets 414. Gas injection inlets 414 pass through top
dielectric plate 404, are bonded to the top dielectric plate 404,
and enter middle dielectric plate 406 where they join showerhead
zone cavities 416. Showerhead zone cavities 416 provide process
gases to showerhead injection holes 418. Passing through
alternative ICP source 400 is optical plug 110 (or an optical
viewport) that hermetic metal seal flange 420 connects to top
vacuum plate 402. Middle ceramic plate 406 includes distributed
cooling water channels 422 that support coil segments 424 on their
sidewalls. These coil segments may be formed by plating of the
coolant channels.
[0082] FIG. 13 shows an alternative cross section of ICP source 400
of FIG. 12. As FIG. 13 indicates, coolant inlet and outlet 426
allow coolant flow through the ICP source housing 400 via the
coolant channels 422 formed in the middle dielectric plate 406.
Moreover, electrical contact leads 428 allow electrical connections
of the multi-zone ICP source cool segments 424 to the external
capacitors and RF power supply.
[0083] FIG. 14 illustrates in more detail the structure of middle
dielectric plate 406 of the present embodiment. As FIG. 14
indicates, RF coil segments 424 line cooling water channels 422.
This eliminates the need for formation of deeper coolant channels
for cooling RF coil segments. In addition, gas dispersion cavities
416 are formed in the middle dielectric plate 406 for uniform
distribution and injection of the process gases via the bottom
dielectric plate 408. Opening 426 of middle dielectric plate 406 is
of sufficient size to permit passage of optical plug 110 for
in-situ plasma process monitoring and control applications.
[0084] Consequently, differences between hermetically-sealed
multi-zone ICP source 300 of FIGS. 5 through 9 and multi-zone ICP
source 400 of FIGS. 12 through 14 include U-shape metallized
grooves 422 in the middle dielectric plate, as opposed to the fully
filled metallized grooves. As a result of this difference, a second
difference is that multi-zone ICP source 400 eliminates the need
for fabricating cooling grooves in top dielectric plate 404. This
is because the trenches 422 include metallized sidewall and bottom
surfaces to form coil segments 424 and can also allow coolant flow
for ICP source cooling. This results in a simplified ICP source
structure and manufacturing process. As with multi-zone ICP source
300 of FIG. 5, the ICP coil metallization process for multi-zone
ICP source 400 may be performed using one or a combination of
sputtering and electroplating deposition processes.
[0085] Before the ICP source is hermetically bonded to the metallic
vacuum plate or chamber vacuum flanges, the ICP coil segments are
formed as thin (e.g., 10 .mu.m to 1000 .mu.m) layers of metal (Al
or Cu) covering the shallow trench 422 sidewalls and bottom
surface. These metallized regions are formed in the shape of broken
rings in middle dielectric plate 406 top surface. An alternative
embodiment can form the ICP antenna metallized broken rings on the
bottom surface of top dielectric plate 304. The vacuum plate or
flange 402 has embedded coolant channels in order to perform
additional cooling in the ICP source structure.
[0086] With multi-zone ICP source 400, it is also possible to place
the ICP coil segments 424 between the showerhead 408 and middle
dielectric plate 406 by using metallized shallow grooves either on
top surface of showerhead plate 408 or on bottom surface of middle
dielectric plate 406. Moreover, by using a hermetic bonding process
for the overall assembly of the multi-zone ICP source and by
providing embedded cooling channels in the top vacuum plate 402,
the ICP source cooling can be performed by the top metallic plate
402 and the dielectric coolant grooves 422 can be eliminated. This
eliminates the need for top dielectric plate 404 and reduces the
overall ICP housing stack to two dielectric plates plus the
metallic vacuum lid 402. In this configuration, ICP coil segments
424 may be placed between the gas dispersion trenches 422 on the
gas showerhead plate 408. Moreover, they can be used as part of the
bonding structure for hermetic sealing of the showerhead plate 408
to its adjacent dielectric plate 406 which itself is hermetically
sealed/bonded to the metallic top plate 402. This simplified
multi-zone ICP structure is the fourth embodiment illustrated in
FIGS. 15 through 21.
[0087] In order to reduce the eddy current RF losses into the
metallic top plate 402 and maximize the RF coupling efficiency to
the plasma environment, a series of radial strips of a permeable
soft magnetic material or a ferromagnetic material (e.g., nickel,
iron, etc.) may be placed between the metallic top plate 402 and
the multi-zone ICP source 400 housing prior to structural bonding.
This may be done by depositing the high-permeability magnetic
material on metallic top plate 402 using electroplating techniques.
Alternatively, shallow radial grooves may be formed in the metallic
top plate 402 on its vacuum side and thin rods of high-permeability
material (iron or nickel or another ferromagnetic material) may be
inserted within these grooves prior to the hermetic bonding process
to seal the multi-zone ICP source 400 housing to metallic top plate
402. These high-permeability magnetic material segments provide
radial paths to close the magnetic field lines over ICP coil
segments 424, resulting in improved RF coupling efficiency to the
internal plasma environment.
[0088] FIGS. 15 through 21, therefore, show a hermetically sealed
ICP source 500 with six coil segments and six showerhead injection
zones. In general, the design shown here is applicable to any
number of coil segments 518 and any number of showerhead injection
zones 516. Various designs with equal or different numbers of coil
segments and injection zones are possible.
[0089] Thus, FIGS. 15 through 21 show yet another alternative
embodiment of the present invention including vacuum plate 502 that
adjoins top dielectric plate 504. Dielectric plate 504 adjoins
modified showerhead plate 506. Optical plug or viewport 110 fits
within ICP source 500 and is sealed by hermetic metal seals using
viewport metallic flange 508. This permits an optical view access
through optical plug 110 to the substrate within the plasma process
chamber. Vacuum plate or flange 502 includes numerous channels 510
for receiving multi-zone gas inlet tubes 512. Gas inlet tubes 512
go to process gas dispersion channels 514 within top dielectric
plate 504. Process gas injection holes 516 connect to process gas
dispersion channels 514 for directing process gases through
modified showerhead plate 506. In alternative multi-zone ICP source
500, RF coil segments 518 are formed integral to modified
showerhead plate or bottom dielectric plate 506. In this
configuration, there is no need for additional cooling of RF coil
segments 518, since effective cooling of the bonded ICP structure
is provided by the embedded coolant channels in the vacuum plate or
flange 502.
[0090] FIG. 15 shows a stack consisting of three bonded plates. The
top plate is a water-cooled stainless steel vacuum plate or flange
(typically 14" to 20" in diameter for 200-mm wafer processing (20"
diameter for CVC's Universal Plasma Module). Gas inlets 512 in the
FIG. 15 embodiment are bonded to the top dielectric plate and
flushed/butted against the multi-zone gas dispersion cavities 514.
Six cavities 514 are shown along with twelve gas inlet tubes
512.
[0091] On the other hand, FIG. 16 illustrates six of the twelve
electrical RF rods 520 connected to the multi-zone ICP coil
segments 518 on the lower dielectric plate or showerhead plate S06.
These RF connector rods are thermally bonded, and/or shrink-fit
assembled, inside the upper dielectric plate.
[0092] Electrical rods 520 are flushed against the bottom surface
of the upper dielectric plate 504 and are subsequently fused or
bonded to the electrical terminals on the antenna coil segments
that appear on FIG. 20. The bottom and top dielectric plates are
bonded together on a continuous ring around the edge region as well
as on circular bonded junctions (continuous rings) formed between
any pair of adjacent coil segments. This will also ensure excellent
thermal contact between the top dielectric plate 504 and bottom
dielectric plate 506. The coil segments can provide additional
bonding surface area for improved thermal contact.
[0093] FIG. 17 shows a top view of vacuum plate 502 of multi-zone
ICP source 500. In particular, vacuum plate 502 top view includes
vacuum plate coolant inlets 522 and 524 that receive cooling water
(or any coolant) for ICP source 500. Cooling water outlets 526 and
528 permit the cooling water to exit multi-zone ICP source 500 for
effective heat removal. Gas inlet tubes 512 are shown within
channels 514. As is the case with earlier described embodiments,
the SH-61 and SH-62 gas inlets correspond to the outermost gas
rings of showerhead 506. The decreasing number "SH" associated with
the gas inlets 512 correspond to the more inward injection rings of
showerhead plate 506. Vacuum plate 502 top surface also includes
electrical feedthroughs 530 for connecting to ICP antenna RF coil
segments 518 and showerhead plate 506. In the FIG. 17 embodiment,
electrical feedthroughs 530 include twelve terminals for six
antenna coil segments that connect to the six RF coil segments
formed on showerhead plate 506.
[0094] For the bonded monolithic structure shown in FIGS. 15
through 21, the water-cooled vacuum plate 502 provides effective
cooling of the entire multi-zone ICP source 500 and its associated
dielectric housing. This effective cooling is possible since the
entire ICP housing bonds together to the metallic vacuum plate. The
structural bonding minimizes the thermal resistances between the
adjacent dielectric plates 504, 506 as well as between the top
dielectric plate 504 and water-cooled vacuum plate 502. Moreover,
the multi-zone ICP dielectric housing material can be made of
aluminum nitride (AlN) which has a relatively high thermal
conductivity on the order of 170 W/m-K. According to FIG. 17, the
metallic (stainless steel) vacuum plate or flange provides a number
of through holes for various multi-zone ICP source
feedthroughs.
[0095] FIG. 18 shows a bottom view of vacuum plate 502 of the FIG.
13 embodiment. In particular, the bottom view of vacuum plate 502
shows gas inlets 512 emanating from through channels 514 as well as
electrical feedthroughs 530 that pass through vacuum plate 502. In
addition, the bottom view of vacuum plate 502 shows embedded radial
ferromagnetic rods 532 that are made of a high permeability
magnetic material. For example, in one embodiment embedded radial
rods 532 may be 8" long by 0.5" wide by 0.25" thick rods of iron or
nickel or a more suitable ferromagnetic material with low
eddy-current losses that are inserted into same size grooves at the
bottom surface of vacuum plate 502. In FIG. 18, there are ten
radial rods 532 in vacuum plate 502.
[0096] Radial rods 532 that FIG. 18 shows are embedded within
grooves in vacuum plate 502 and may be made of a magnetic material
such as high permeability iron or nickel and provide radial paths
to close the magnetic field lines below the vacuum plate. This will
result in a reduction of eddy current losses into the metallic
vacuum plate and improves the overall multi-zone ICP source 500 RF
power coupling efficiency into the plasma environment. If
necessary, radial rods 532 may be replaced with a blanket plated
layer of iron or nickel on vacuum plate 502 (in this case the rods
and grooves will not be needed).
[0097] For the specific design presented here, the vacuum plate has
12 holes for showerhead gas inlet tubes (SH-11, SH-12, SH-21,
SH-22, SH-31, SH-32, . . . ), and another set of 12 holes for
multi-zone ICP electrical connections. Moreover, there is a center
hole (0.5" to 1.5" in diameter) which is used for insertion of the
optical viewpoint. The metallic vacuum plate (14" to 20" in
diameter) has a thickness of 0.25" to 0.50" for providing vacuum
mechanical strength.
[0098] FIG. 19 shows modified showerhead plate 506 of the FIG. 15
embodiment. Modified showerhead assembly 506 is formed of a
dielectric material such as aluminum nitride, aluminum oxide, boron
nitrites or another suitable material and includes injector holes
516 and ICP coil segments 518. ICP coil segments 518 are bonded to
the top portion of ICP showerhead plate 506 as six monolithic coil
segments. Showerhead injector holes 516 include six rings of holes,
each hole with a diameter in the range of 0.02 inches to 0.06
inches, with a total number of holes for each injector zone 1
through 6 ranging from 50 to 500 (outer rings to have more holes).
Center hole 534 has a diameter of between 0.25 inches and 1.0
inches for passage of optical plug 110. ICP coil segments 518 fit
within grooves 536 of modified showerhead 506 which have a depth of
0.001 to 0.1 inches and a width of 0.25 to 0.5 inches.
[0099] FIG. 20 shows the top surface view of modified showerhead
plate 506. Modified showerhead 506 includes, in the FIG. 20
embodiment, six monolithic coil segments 518 that fill substrate
grooves 536 (see FIG. 19) and include terminals 538 and 540 for
external RF connections to external RF capacitor circuits. The
showerhead 506 embodiment that FIG. 20 shows includes injector
holes 516 for injecting processed gas into the process chamber for
plasma processing of various substrates.
[0100] Bottom dielectric plate 506 serves two purposes. One is to
provide multi-zone process gas injection, the other is to house
coil segments 518 (formed by preformed metal segments to be
sandwiched between the two dielectric plates or formed by
sputtering and/or plating on dielectric plate 506) which are made
of a suitable material such as aluminum or copper. Coil segments
518 fill shallow grooves (0.001" to 0.100") shaped as broken rings.
The surface of dielectric plate 506 may be planarized using a
mechanical polishing process, for example after filling the shallow
trenches with metal.
[0101] FIG. 21 shows a bottom surface view of top dielectric plate
504 of the FIG. 15 embodiment. Attaching to top dielectric plate
504 are stainless steel tubes 512 for providing plasma process gas
to gas dispersion cavities 514. Stainless steel tubes 512 are
bonded stainless steel tubes for multi-zone gas injection through
gas dispersion cavities 516, with two tubes positioned 180.degree.
apart for each gas dispersion cavity ring. Bonded aluminum rods 520
form six pairs for electrically connecting coil segments 518 to
external RF capacitors and RF power supplies. FIG. 21 also shows
opening 534 for passage of optical plug 110. Compared to the
previous multi-zone ICP source embodiments of this invention, this
last design offers some advantages due to its simplified structure
and reduced fabrication cost.
[0102] Gas dispersion cavities 514 are formed as ring-shaped
cavities (0.25"-0.50" wide by 0.25" to 0.50" deep). These cavities
will overlay the multi-zone injector holes 516 in the bottom
dielectric plate. Also shown in FIG. 21 are the gas inlet tube ends
520 (twelve tubes shown for a six-zone injector) located within the
gas dispersion cavities. Each pair of inlet tubes are connected
together externally to a single gas control manifold and valve to
form a controlled six-zone (or n-zone with n=1,2,3, . . . ) process
gas injector.
[0103] Materials that work well to form dielectric plate 504 and
modified showerhead 506 are numerous. However, certain materials
are particularly preferred for the present embodiment. These
materials include boron nitride, aluminum nitride and aluminum
oxide. The reasons why these materials (e.g., AlN and BN) are
preferable are discussed briefly to explain their advantages.
[0104] Boron nitride (BN)is highly refractory material with
physical and chemical properties similar to carbon. Graphite-like
(g-BN), wurzite (w-BN) and zinc blend (z-BN) are known polymorphs
of BN corresponding to the graphite (hexagonal) and diamond (cubic)
structures. Transformation of g-BN to w-BN occurs at pressures
above 12 GPa at relatively low temperature (230.degree. C.).
Transformation of w-BN to z-BN occurs above 1300.degree. C. and
pressures above 5.5 GPa. Zinc blend (z-BN) is stable above 5.5 GPa
and from 1100.degree. to 1500.degree. C.
[0105] All forms of BN are good electrical insulators, possessing
band gaps of several electron volts (eV); electrical resistance of
the hexagonal from varies from 1.7.times.10.sup.13 ohm-cm at
25.degree. C. to 3.times.10.sup.4 ohm-cm at 1000.degree. C. and is
little affected by frequency. The dielectric constant of hexagonal
BN is 3 with the electric vector parallel to the oasal plane and 5
perpendicular to the plane. Consistent with the short interatomic
distances and light atomic weights, all forms of BN are very good
thermal conductors. Boron nitride is chemically inert in most
environments, resisting attack by mineral acids or wetting by
glasses, slags and molten oxides, cryolite and fused salts, and
most molten metals including aluminum. Its rate of oxidation in air
is negligible below 1100.degree. C.
[0106] Hexagonal boron nitride is commonly synthesized as a fine
powder. Powders will vary in crystal size, agglomerate size, purity
(including percent residual B.sub.2O.sub.3) and density. BN powders
can be used as mold release agents, high temperature lubricants,
and additives in oils, rubbers and epoxies to improve thermal
conductance of dielectric compounds. Powders also are used in
metal-and ceramic-matrix composites to improve thermal shock and
modify wetting characteristics.
[0107] Hexagonal boron nitride may be hot pressed into soft (Mohs
2) and easily machinable, white or ivory billets having densities
90-95% of theoretical value(2.25 g/cm.sup.3). Thermal
conductivities of 17-58 W/m-K and CTEs of
0.4-5.times.10.sup.-6/.degree. C. are obtained, depending on
density, orientation with respect to pressing direction and amount
of boric oxide binder phase. Because of its porosity and relatively
low elastic modules (50-75 GPa), hot pressed boron nitride has
outstanding thermal shock resistance and fair toughness. Pyrolytic
boron nitride, produced by chemical vapor deposition on heated
substrates, also is hexagonal; the process is used to produce
coatings and shapes having thin cross sections.
[0108] Cubic boron nitride is second in hardness only to diamond.
It is used for high-performance tool bits and in special grinding
applications. Cubic BN tooling typically outlasts alumina and
carbide tooling and is preferred in applications where diamond is
not appropriate, such as grinding of ferrous metals. Aluminum
Nitride (AlN) has a molecular weight of 40.99, density of 3.26
g/cm.sup.3, CTE of 4.6.times.10.sup.-6/.degree. C., m.p. of
2200.degree. C. under 4 atm of N.sub.2, and sublimes at 1 atm. AlN
has a white, hexagonal crystal structure and its powder hydrolyses
on contact with water or water vapor. Water-resistant powders that
allow aqueous processing are commercially available. AlN is stable
against acids and only slightly reacts with bases. It is made by
reacting aluminum metal with nitrogen, by reduction of aluminum
oxide with carbon in the presence of nitrogen or ammonia, or by
decomposition of the product of reaction between aluminum
trichloride and ammonia. AlN powder may be sintered to full density
above 1800.degree. C. in 1 atm of N.sub.2 with the addition of
sintering aids such as Y.sub.2O.sub.3 or CaO. Thermal conductivity
in excess of 200 W/mK can be achieved in sintered parts, which is
five times that of aluminum oxide. The dielectric strength of AlN
is 1.5 times that of aluminum oxide, and electrical resistivity and
mechanical strength are comparable to that of aluminum oxide. Its
dielectric constant is about half that of aluminum oxide. Major
applications include thermally conductive substrates and heat sinks
for semiconductors, automotive and transit power modules, mobile
communications and multichip modules. Other properties of AlN
appear in the following table.
1 Properties of Aluminum Nitride Units AlN Volume ohm-cm
.gtoreq.10.sup.14 resistivity Dielectric RT-1 MHz 8.6 constant
Dielectric RT-1 MHz 0.0005 loss Thermal W/mK 170 conductivity
Temperature 10.sup.-6/.degree. C. 4.7 coeff. of expansion
RT-400.degree. C. Density g/cm.sup.3 3.3 Hardness GPa 11.8 (Knoop)
Bending MPa 276 strength Youngs GPa 331 modules Poisson ratio 0.25
Fracture MPa{square root}m 3.44 toughness via chevron notch shorbar
technique
[0109] FIG. 22 demonstrates the schematic diagram of a plasma
equipment process chamber 600 comprising one of the multi-zone ICP
structures of this invention. The particular example shown in FIG.
22 shows a three-zone configuration in conjunction with three RF
power supplies for the ICP source structure. The multi-zone ICP
source structure 601 employs a hermetically bonded structure of
dielectric plates (e.g., made of a ceramic material with relatively
high thermal conductivity) containing the ICP antenna coils and gas
showerhead dispersion cavities (not shown). The ICP housing 601 is
also hermetically bonded and sealed to the metallic vacuum plate or
flange 603. The vacuum plate or flange 603 is placed onto the
plasma equipment process chamber 605 and established chamber vacuum
using vacuum seal 622. This configuration places the multi-zone ICP
housing on the vacuum side 620 of the process chamber 605. The ICP
source 601 provides a vacuum-sealed optical (e.g., sapphire or
quartz) plug or viewport 604 for real-time in-situ process
monitoring and control purposes by monitoring the plasma process
side 620 and/or substrate 607 state parameters. For instance, FIG.
22 shows a full wafer interferometry sensor 617 mounted on top of
the optical plug 604 for real-time in-situ monitoring and control
of the plasma process uniformity on the substrate 607. Other
in-situ sensors such as plasma emission sensors and spatially
resolved plasma emission sensors may also be used for process
monitoring and control purposes.
[0110] The multi-zone ICP source 601 is positioned over a chuck 606
supporting the substrate 607 to be processed. Preferably, chuck 606
controls the substrate 607 temperature by controlled heating and/or
cooling during the plasma process. The substrate 607 is preferably
clamped to the temperature-controlled chuck 606 either by
electrostatic or mechanical means. Moreover, the chuck 606
preferably has a capability for up/down movement and height
adjustment with respect to the ICP source housing 601. This will
provide a very useful capability for adjusting the ICP source to
substrate spacing in order to optimize the plasma process
parameters such as process uniformity while maintaining sufficient
process throughput. For instance, reducing the ICP source to
substrate spacing results in increased plasma density and ion
current density at the wafer, causing enhanced plasma process rate.
If the ICP source to substrate spacing becomes too small, the
process uniformity may degrade and there may also be additional
problems associated with plasma-induced device damage and excessive
eddy-current heating of the substrate 607.
[0111] The plasma process chamber provides a vacuum chamber access
valve for automated loading and unloading of the substrate 607 into
and out of the vacuum process chamber 605. Moreover, the plasma
process chamber 605 connects to a vacuum pump (e.g., turbo pump
and/or mechanical pump) via pump port 629.
[0112] The chuck 606 preferably provides an option for electrical
biasing (e.g., 13.56 MHZ RF or 100 kHz-400 KHz AC power supply) of
the substrate 607 via power supply 614 and coupling capacitor 615.
This electrical bias provides a good control over the plasma ion
energy impacting the substrate 607.
[0113] FIG. 22 shows a three-zone ICP configuration with the outer
zone, middle zone, and inner zone powered by the RF power supplies
RF.sub.1 (608), RF.sub.2 (609), and RF.sub.3 (610), respectively.
As shown in this FIGURE, the RF power supplies are connected to the
ICP antenna zones, preferably via series blocking capacitors 630,
631, and 632. Moreover, external inter-segment series capacitors
C.sub.1 (611), C.sub.2 (612), and C.sub.3 (613) connect the antenna
segments in series within each zone (outer zone, middle zone, and
inner zone, respectively). These series capacitors ensure reduced
induced RF voltages within various zones, resulting in improved
inductive plasma coupling and reduced parasitic capacitive coupling
of the energy source to the plasma medium. The multi-zone ICP 601
RF power supplies (608, 609, 610) may employ source frequencies
over a wide range (e.g., 1 MHZ to over 30 MHZ), and preferably a
fixed 13.56 MHZ frequency. Moreover, these multi-zone power
supplies may use external RF matching networks (not shown in FIG.
22) placed between the RF power supplies and the ICP antenna zones
for improved load matching, improved RF power coupling, and
improved plasma process repeatability. The RF power supplies may
also employ phase shifters 616 in order to control the phase angles
among various RF power supplies for improved process uniformity and
repeatability.
[0114] The phase shifters 616 become non-essential when the power
supplies use different frequencies. For instance, if a 100 kHz
power supply is used for the substrate bias and three 13.56 MHZ RF
power supplies are employed for powering the multi-zone ICP
antenna, there is no need for a phase shifter between the substrate
power supply and the multi-zone ICP power supplies. The ICP RF
power supplies, however, may employ phase shifters/controllers to
control the phase angles for RF.sub.1 (608), RF.sub.2 (609), and
RF.sub.3 (610).
[0115] FIG. 22 also shows the coolant inlet 633 and coolant outlet
634 lines for flowing the coolant (e.g., cooling water) through the
metallic vacuum lid. Due to the hermetically sealed bonded
structure of the ICP source with the thermally conductive
bonded/sealed interfaces 640 (between the top dielectric plate and
the metallic vacuum lid) and 641 (between the lower and upper
dielectric or ceramic plates), the cooled metallic vacuum plate/lid
also serves as an effective heat removal or heat sink medium for
the ICP housing. This will ensure that the ICP housing temperature
with maximum RF power levels running through the antenna segments
will remain well below 100.degree. C.
[0116] As shown in FIG. 22, the ICP process gases 635 are fed to
the ICP showerhead plate 602 via the gas manifolds 618 and 619. The
external manifolding of the ICP gas lines can be designed to meet
the specific plasma process uniformity and defect density
requirements. The gas injection system can be set up for either
single-zone or multi-zone gas injection (a two-zone injection using
two gas manifolds is shown in FIG. 22).
[0117] FIG. 23 shows an example of a two-manifold gas injection
configuration 700 used with the multi-zone ICP source structures of
this invention. FIG. 23 shows six pairs of gas inlet lines 703 for
the multi-zone ICP source. The schematic diagram of FIG. 23 also
shows up to six different process gases 704 and 705 coming from the
ICP equipment gas box. The multi-zone ICP source dispersion
cavities employ one pair of inlets for each gas dispersion cavity
corresponding to each gas injection ring of holes in the
showerhead. For instance, SH-61 and SH-62 both connect to the sixth
(or outermost) gas dispersion cavity in the multi-zone ICP source
structure while the inlet lines SH-11 and SH-12 both connect to the
first (or innermost) gas dispersion cavity. As shown in the example
of FIG. 23, process gases A, B and C (705) are connected together
via the first gas manifold 701 and subsequently inject into the
showerhead injection rings 2, 4, and 6. On the other hand, process
gases D, E, and F (704) are connected together using the second gas
manifold 702 and subsequently inject into the plasma process
chamber via the showerhead injection rings 1, 3 and 5 (SH-11/SH-12,
SH-31/SH-32, and SH-51/SH-52 inlets). This arrangement effectively
configures the multi-zone ICP injector as a two-zone showerhead
where premixing of the first group of process gases 705 and the
second group of process gases 704 is prevented. It should be
understood that other gas connection configurations and zone
partitioning arrangements are possible for the multi-zone ICP
structures of this invention.
[0118] FIGS. 24A and 24B illustrate a three-zone and a two-zone ICP
mixing arrangement, respectively, for one embodiment of this
invention with six antenna segments. As shown in FIG. 24A, an RF
power supply 801 is used to provide substrate bias via series or
blocking capacitor 814. Moreover, the ICP antenna segments (six
segments in this example) are externally partitioned and wired to
form three ICP zones (edge zone 811, middle zone 812, and center
zone 813). In edge zone 811, the outer two antenna segments
(segments 1 and 2 with connector nodes C.sub.11/C.sub.12 and
C.sub.21/C.sub.22) employ a series capacitor 808 to bridge the two
segments. A first RF.sub.1 power supply 803 connects to C.sub.11
and C.sub.22 via series blocking capacitor 815. The middle zone 812
is formed by bridging the third and fourth antenna segments using a
series capacitor 809 placed between nodes C.sub.32 and C.sub.41. A
second RF.sub.2 power supply 805 powers the middle zone 812 via
series blocking capacitor 816. Inner zone 813 is configured by
combining the fifth and sixth antenna segments using a series
capacitor 810 placed between nodes C.sub.52 and C.sub.61. A third
RF.sub.3 power supply 807 powers the inner zone via series blocking
capacitor 817. Three phase shifters/controllers 802, 804, 806 may
be used in order to control the relative phase angles of various RF
power supplies for process uniformity and repeatability. For a
given multi-zone ICP source structure, various types of ICP antenna
segment partitioning may be used for a given number of zones. In
the example shown in FIG. 24A, each antenna zone has received two
adjacent antenna segments. The optimum partitioning configuration
should provide the best amount of control over plasma process
uniformity.
[0119] FIG. 24B illustrates a two-zone ICP arrangement wherein the
outer zone is formed by grouping the first and second antenna
segments while the inner zone is configured by grouping the third
through sixth antenna segments. The outer zone employs a series
capacitor between nodes C.sub.12 and C.sub.21 in conjunction with a
first RF.sub.1 power supply 905 connected to nodes C.sub.11 and
C.sub.22 via a series blocking capacitor 913. The inner zone
utilizes series capacitors 908 (between nodes C.sub.32 and
C.sub.41), 909 (between nodes C.sub.42 and C.sub.51) and 910
(between nodes C.sub.52 and C.sub.61). A second RF.sub.2 power
supply 906 connects to inner zone nodes C.sub.31 and C.sub.62 via
series blocking capacitor 914. An RF power supply 901 connects to
the plasma equipment chuck via series blocking capacitor 902 in
order to produce substrate RF bias. Phase shifters/controllers 903
and 904 may be used in order to control the relative phase angles
of various RF power supplies.
[0120] One important advantage of the multi-zone ICP structures and
methods of this invention is that for any given source structure
numerous multi-zone wiring arrangements and antenna segment
partitioning configurations are possible simply by changing the
electrical wiring external to the source. Therefore, this invention
provides a significant amount of flexibility for optimizing the
multi-zone ICP source zoning and partitioning in order to establish
the widest possible plasma process window and the best process
uniformity. Moreover, the multi-zone ICP source structures and
methods of this invention are scalable to allow uniform processing
of larger substrates such as 300-mm silicon wafers and large-area
flat-panel display substrates.
[0121] The hermetic sealing fabrication method preferably used for
fabrication of the multi-zone ICP source structures of this
invention result in extremely high vacuum integrity, ultra-high
vacuum (UHV) compatibility, and ultra-clean plasma processing. For
instance, the multi-zone ICP source structures of this invention
are compatible with vacuum base pressures as low as
5.times.10.sup.-9 Torr and better.
[0122] For a given multi-zone ICP source structure and a specified
process application, the optimum zoning and antenna segment
partitioning (or grouping) between the antenna zones can be
obtained by performing a series of Design-of-Experiments (DOE) with
various external wiring configurations. The multi-zone ICP series
capacitors are selected to minimize the antenna RF voltages within
various zones depending on the RF frequency.
[0123] In most practical plasma process applications, the
multi-zone ICP structures of this invention can meet the process
requirements using a two-zone or a three-zone configuration (e.g.,
two-zone configuration for up to 200-mm wafer processing). Larger
substrates (e.g., 300-mm silicon wafers) may benefit from a higher
number of zones. A multi-variable real-time controller may be used
in conjunction with a suitable sensor (e.g., a full-wafer
interferometry sensor) in order to control the process uniformity
and repeatability.
[0124] The multi-zone ICP structures of this invention may employ
either straight lined-up electrical connection feedthroughs for the
ICP antenna segments (as described and shown for various
embodiments) or they may utilize staggered electrical feedthroughs
in order to prevent any possible plasma process non-uniformities
associated with the lined up segment ring breaks in a non-staggered
arrangement. For instance, for a multi-zone ICP structure with
eight circular antenna segments, one type of design may employ
eight pairs of electrical feedthrough connector leads lined up
along two straight (nearly radial) lines extending between the
center and edge regions of the ICP housing. In this design, there
may be some plasma density non-uniformity directly underneath the
source (and very close to the source) and between the two segment
feedthrough lines. This possible non-uniformity can be produced due
to the break in the current flow through each broken antenna
segment ring and due to the cumulative non-uniformity effects of
the non-staggered or straight lined-up feedthroughs. On the other
hand, the eight pairs of feedthroughs for eight broken ring antenna
segments can be staggered at, for instance, 40.degree. to
45.degree. for each pair of adjacent segments in order to utilize
the full 360.degree. planar staggering of the feedthroughs in a
spiral pattern. This will eliminate the possible cumulative
non-uniformity effects of various antenna segment breaks and
associated feedthroughs. Thus, the minimum allowable ICP
source-to-substrate spacing for acceptable plasma process
uniformity is smaller in the case of staggered electrical
feedthroughs (e.g., spiral staggered feedthrough pattern) compared
to the non-staggered feedthrough pattern.
[0125] Due to the proximity of the gas dispersion cavities to the
multi-zone antenna segments in various ICP embodiments of this
invention, there is a possibility of plasma formation within the
gas dispersion cavities. This possible plasma formation in the gas
dispersion cavities can be avoided by various means and techniques.
One method is to fill the gas dispersion cavities with a suitable
ceramic fiber or ceramic powder (e.g., with controlled spherical
ceramic particle size). Filling the gas dispersion cavities with a
ceramic powder or a ceramic filler can be performed prior to final
assembly and hermetic bonding of the multi-zone ICP source
structure.
[0126] The multi-zone ICP source structures of the present
invention may use separate RF power supplies and dedicated matching
networks for each of the ICP antenna zones (e.g., three RF power
supplies and three RF matching networks for a 3-zone ICP source
wiring arrangement). Another method, however, is to electrically
wire the zones in parallel with either a fixed capacitor or a
variable capacitor connected in series with each of the zones in
order to adjust the effective load impedance and electrical current
associated with each zone. Another possibility is to use adjustable
(e.g., mechanically adjustable with server or stepper motors)
transformer couplings for various zones with a single transformer
primary coil attached to a single RF power supply and a single RF
matching network (RF matching network may not be needed). These
possible arrangements allow effective real-time multi-zone ICP
plasma uniformity control with a single RF power supply, resulting
in reduced system cost and complexity. FIGS. 25A and 25B show
examples of two power supply wiring arrangements enabling 3-zone
ICP operation and control using a single RF power supply. FIG. 25A
shows a parallel capacitive wiring arrangement while FIG. 25B
demonstrates an adjustable transformer coupling configuration
allowing multi-zone operation. A real-time multi-variable
controller will provide control signals for the stepper or servo
motors controlling the variable capacitor valves or the extent of
transformer coupling ratios. For instance, a multi-variable
real-time controller will adjust the multi-zone transformer
coupling ratios M.sub.1, M.sub.2, and M.sub.3 for real-time
multi-zone uniformity control.
[0127] Although the invention has been described in detail herein
with reference to the illustrative embodiments, it is to be
understood that this description is by way of example only and is
not to be construed in a limiting sense. It is to be further
understood, therefore, that numerous changes in the details of the
embodiments of the invention and additional embodiments of the
invention, will be apparent to, and may be made by, persons of
ordinary skill in the art having reference to this description. It
is contemplated that all such changes and additional embodiments
are within the spirit and true scope of the invention as claimed
below.
* * * * *