U.S. patent application number 13/084343 was filed with the patent office on 2012-10-11 for multi-frequency hollow cathode system for substrate plasma processing.
This patent application is currently assigned to Lam Research Corporation. Invention is credited to John Patrick Holland, Peter L. G. Ventzek.
Application Number | 20120255678 13/084343 |
Document ID | / |
Family ID | 46965179 |
Filed Date | 2012-10-11 |
United States Patent
Application |
20120255678 |
Kind Code |
A1 |
Holland; John Patrick ; et
al. |
October 11, 2012 |
Multi-Frequency Hollow Cathode System for Substrate Plasma
Processing
Abstract
A hollow cathode system is provided for plasma generation in
substrate plasma processing. The system includes a plurality of
electrically conductive plates stacked in a layered manner.
Dielectric sheets are disposed between each adjacently positioned
pair of the plurality of electrically conductive plates. A number
of holes are each formed to extend through the plurality of
electrically conductive plates and dielectric sheets. The system
also includes at least two independently controllable
radiofrequency (RF) power sources electrically connected to one or
more of the plurality of electrically conductive plates. The RF
power sources are independently controllable with regard to
frequency and amplitude.
Inventors: |
Holland; John Patrick; (San
Jose, CA) ; Ventzek; Peter L. G.; (San Francisco,
CA) |
Assignee: |
Lam Research Corporation
Fremont
CA
|
Family ID: |
46965179 |
Appl. No.: |
13/084343 |
Filed: |
April 11, 2011 |
Current U.S.
Class: |
156/345.33 ;
156/345.44 |
Current CPC
Class: |
H01J 37/32596
20130101 |
Class at
Publication: |
156/345.33 ;
156/345.44 |
International
Class: |
C23F 1/08 20060101
C23F001/08 |
Claims
1. A hollow cathode system for plasma generation in substrate
plasma processing, comprising: a plurality of electrically
conductive plates stacked in a layered manner; dielectric sheets
disposed between each adjacently positioned pair of the plurality
of electrically conductive plates; a number of holes each formed to
extend through the plurality of electrically conductive plates and
dielectric sheets; and at least two independently controllable
radiofrequency (RF) power sources electrically connected to one or
more of the plurality of electrically conductive plates.
2. A hollow cathode system for plasma generation in substrate
plasma processing as recited in claim 1, wherein a first end of
each of the number of holes is in fluid communication with a
process gas source, and wherein a second end of each of the number
of holes is in fluid communication with a substrate processing
region.
3. A hollow cathode system for plasma generation in substrate
plasma processing as recited in claim 1, wherein each of the at
least two independently controllable RF power sources is
independently controllable with regard to RF power frequency and
amplitude.
4. A hollow cathode system for plasma generation in substrate
plasma processing as recited in claim 3, wherein each of the at
least two independently controllable RF power sources is defined to
generate RF power having a frequency of either 2 megaHertz (MHz),
27 MHz, 60 MHz, or 400 kiloHertz (kHz).
5. A hollow cathode system for plasma generation in substrate
plasma processing as recited in claim 1, wherein the plurality of
electrically conductive plates includes a top ground plate, a
central cathode plate connected to receive RF power from each of
the at least two independently controllable RF power sources, and a
bottom ground plate.
6. A hollow cathode system for plasma generation in substrate
plasma processing as recited in claim 1, wherein the plurality of
electrically conductive plates includes multiple cathode plates
separated from each other by dielectric sheets, wherein each of the
multiple cathode plates is connected to receive RF power from one
or more of the at least two independently controllable RF power
sources.
7. A hollow cathode system for plasma generation in substrate
plasma processing as recited in claim 6, wherein the plurality of
electrically conductive plates includes a top ground plate.
8. A hollow cathode system for plasma generation in substrate
plasma processing as recited in claim 7, wherein the plurality of
electrically conductive plates includes a bottom ground plate.
9. A hollow cathode system for plasma generation in substrate
plasma processing as recited in claim 6, wherein at least one of
the multiple cathode plates that is to be exposed to a higher
pressure process gas within the number of holes is connected to a
lower frequency one of the at least two independently controllable
RF power sources.
10. A hollow cathode system for plasma generation in substrate
plasma processing as recited in claim 6, wherein at least one of
the multiple cathode plates that is to be exposed to a lower
pressure process gas within the number of holes is connected to a
higher frequency one of the at least two independently controllable
RF power sources.
11. A system for substrate plasma processing, comprising: a chamber
formed by surrounding walls, a top plate, and a bottom plate; a
substrate support disposed within the chamber; a hollow cathode
assembly disposed within the chamber above and spaced apart from
the substrate support; a process gas source in fluid communication
with the hollow cathode assembly to supply process gas to the
hollow cathode assembly; and a plurality of radiofrequency (RF)
power sources in electrical communication with the hollow cathode
assembly, wherein each of the plurality of RF power sources is
independently controllable with regard to RF power frequency and
amplitude, wherein during operation of the system, a plurality of
RF powers respectively transmitted from the plurality of RF power
sources to the hollow cathode assembly transform the process gas
into a plasma within the hollow cathode assembly, such that
reactive species with the plasma move from the hollow cathode
assembly to a substrate processing region over the substrate
support.
12. A system for substrate plasma processing as recited in claim
11, wherein the hollow cathode assembly is defined over an area of
the substrate support upon which a substrate is to be received for
plasma processing, and wherein the hollow cathode assembly includes
multiple hollow cathodes each defined in exposure to a processing
region within the chamber between the hollow cathode assembly and
the substrate support, and wherein the multiple hollow cathodes are
distributed in a substantially uniform manner relative to the area
of the substrate support upon which the substrate is to be received
for plasma processing.
13. A system for substrate plasma processing as recited in claim
12, further comprising: a process gas plenum formed within the
chamber above the hollow cathode assembly, wherein the process gas
plenum is in fluid communication with both the process gas source
and each of the multiple hollow cathodes within the hollow cathode
assembly, and wherein the process gas plenum is formed to
distribute the process gas to each of the multiple hollow cathodes
within the hollow cathode assembly in a substantially uniform
manner.
14. A system for substrate plasma processing as recited in claim
13, further comprising: an anode plate disposed within the process
gas plenum and over the hollow cathode assembly, wherein the anode
plate is electrically connected to a negative bias to drive ions
from the multiple hollow cathodes into the processing region.
15. A system for substrate plasma processing as recited in claim
12, further comprising: a process gas supply line connected in
fluid communication between the process gas source and the hollow
cathode assembly, wherein the hollow cathode assembly is formed to
include process gas distribution channels in fluid communication
with the process gas supply line, wherein the process gas
distribution channels are formed to direct the process gas from the
process gas supply line to each of the multiple hollow cathodes
within the hollow cathode assembly in a substantially uniform
manner.
16. A system for substrate plasma processing as recited in claim
15, further comprising: an exhaust plenum formed within the chamber
above the hollow cathode assembly, wherein the hollow cathode
assembly includes multiple exhaust holes formed to extend
completely through the hollow cathode from the processing region to
the exhaust plenum, wherein the multiple exhaust holes are
distributed in a substantially uniform manner relative to the area
of the substrate support upon which the substrate is to be received
for plasma processing, and wherein each of the multiple exhaust
holes is isolated from the multiple hollow cathodes and the process
gas distribution channels within the hollow cathode assembly.
17. A system for substrate plasma processing as recited in claim
12, further comprising: a cathode plate disposed between the hollow
cathode assembly and the processing region, wherein the cathode
plate is electrically connected to a positive bias to pull ions
from the multiple hollow cathodes into the processing region.
18. A system for substrate plasma processing as recited in claim
12, further comprising: a source plasma region formed within the
chamber above the hollow cathode assembly, wherein the source
plasma region is in fluid communication with both the process gas
source and each of the multiple hollow cathodes within the hollow
cathode assembly; and a coil assembly disposed to transform process
gas within the source plasma region into a source plasma, whereby
the source plasma drives secondary plasma generation in each of the
multiple hollow cathodes within the hollow cathode assembly in a
substantially uniform manner.
19. A system for substrate plasma processing as recited in claim
11, wherein each of the plurality of RF power sources is defined to
generate RF power having a frequency of either 2 megaHertz (MHz),
27 MHz, 60 MHz, or 400 kiloHertz (kHz).
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is related to U.S. patent application Ser.
No. ______ (Attorney Docket No.: LAM2P704A), filed on an even date
herewith, and entitled "Multi-Frequency Hollow Cathode and Systems
Implementing the Same," which is incorporated herein by reference
in its entirety.
BACKGROUND OF THE INVENTION
[0002] Conventional hollow cathodes are required to operate at high
pressures on the order of hundreds of milliTorr (mTorr) to
atmospheric. Some conventional hollow cathodes operate most
effectively at pressures on the order of 1 to 10 Torr, and have
interior dimensions sized on the order of millimeters (mm). To be
operable, a conventional hollow cathode's interior cavity diameter
should be within the range of a few plasma sheath thicknesses. It
is this scaling that present a problem for use of conventional
hollow cathodes in some semiconductor fabrication processes, such
as plasma etch processes, where low pressures are required.
[0003] More specifically, conventional hollow cathodes require high
radiofrequency (RF) power to generate a plasma at lower gas
pressures and have relatively large sizes. Conventional hollow
cathodes are not capable of generating high plasma densities with
thin plasma sheath thicknesses under simultaneous conditions of low
frequency RF power, low pressure, and small hollow cathode
dimensions. Therefore, conventional hollow cathodes are not
suitable for use in semiconductor fabrication operations where both
low pressure and low frequency RF power are simultaneously
required, such as in plasma etch operations. It is within this
context that the present invention arises.
SUMMARY OF THE INVENTION
[0004] In one embodiment, a hollow cathode system for plasma
generation in substrate plasma processing is disclosed. The hollow
cathode system includes a plurality of electrically conductive
plates stacked in a layered manner. Dielectric sheets are disposed
between each adjacently positioned pair of the plurality of
electrically conductive plates. Also, each of a number of holes is
formed to extend through the plurality of electrically conductive
plates and dielectric sheets disposed there between. The hollow
cathode system also includes at least two independently
controllable RF power sources electrically connected to one or more
of the plurality of electrically conductive plates.
[0005] In another embodiment, a system is disclosed for substrate
plasma processing. The system includes a chamber formed by
surrounding walls, a top plate, and a bottom plate. A substrate
support is disposed within the chamber. The system also includes a
hollow cathode assembly disposed within the chamber above and
spaced apart from the substrate support. The system also includes a
process gas source in fluid communication with the hollow cathode
assembly to supply process gas to the hollow cathode assembly. The
system further includes a plurality of RF power sources in
electrical communication with the hollow cathode assembly. Each of
the plurality of RF power sources is independently controllable
with regard to RF power frequency and amplitude. During operation
of the system, a plurality of RF powers respectively transmitted
from the plurality of RF power sources to the hollow cathode
assembly transform the process gas into a plasma within the hollow
cathode assembly, such that reactive species with the plasma move
from the hollow cathode assembly to a substrate processing region
over the substrate support.
[0006] Other aspects and advantages of the invention will become
more apparent from the following detailed description, taken in
conjunction with the accompanying drawings, illustrating by way of
example the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1A shows a vertical cross-section of a hollow cathode
assembly, in accordance with one embodiment of the present
invention;
[0008] FIG. 1B shows a horizontal cross-section of the hollow
cathode assembly corresponding to View A-A identified in FIG. 1A,
in accordance with one embodiment of the present invention;
[0009] FIG. 2A shows a plasma density versus process gas pressure
curve for a hollow cathode of a given configuration and dimensions
operating at either a single RF frequency or at DC;
[0010] FIG. 2B shows a plasma density versus process gas pressure
curve for the hollow cathode assembly of FIGS. 1A-1B, in accordance
with one embodiment of the present invention;
[0011] FIGS. 3A-3B show an electrically conductive member of a
hollow cathode system that is formed in multiple parts, in
accordance with one embodiment of the present invention;
[0012] FIGS. 4A-4B show an electrically conductive member of a
hollow cathode system that is formed in multiple parts, so as to
segment an interior cavity into multiple interior cavities, in
accordance with one embodiment of the present invention;
[0013] FIG. 5 shows a vertical cross-section through a
multi-frequency RF powered hollow cathode, in which an interior
cavity of the hollow cathode is shaped to affect process gas
pressure, in accordance with one embodiment of the present
invention;
[0014] FIG. 6A shows the example hollow cathode in which three
electrically conductive cathode plates are disposed and separated
from each other by dielectric sheets, in accordance with one
embodiment of the present invention;
[0015] FIG. 6B shows the example hollow cathode, as a variation of
the hollow cathode of FIG. 6A, in which the lower ground plate is
absent, in accordance with one embodiment of the present
invention;
[0016] FIG. 6C shows the example hollow cathode, as a variation of
the hollow cathode of FIG. 6A, in which three independently
controlled RF power sources are used to supply RF power to the
cathode plates at three different frequencies, in accordance with
one embodiment of the present invention;
[0017] FIG. 6D shows the example hollow cathode in which four
electrically conductive cathode plates are disposed and separated
from each other by dielectric sheets, in accordance with one
embodiment of the present invention;
[0018] FIG. 6E shows an example hollow cathode in which a single
electrically conductive cathode plate is connected to receive
multiple RF power frequencies, in accordance with one embodiment of
the present invention;
[0019] FIG. 7 shows a hollow cathode system for plasma generation
in substrate plasma processing, in accordance with one embodiment
of the present invention;
[0020] FIG. 8 shows a system for substrate plasma processing, in
accordance with one embodiment of the present invention;
[0021] FIG. 9A shows another system for substrate plasma
processing, in accordance with one embodiment of the present
invention;
[0022] FIG. 9B shows a system for substrate plasma processing that
is a variation of the system of FIG. 9A, in accordance with one
embodiment of the present invention;
[0023] FIG. 10 shows a system for substrate plasma processing that
is a variation of the system of FIG. 8, in accordance with one
embodiment of the present invention;
[0024] FIG. 11 shows a system for substrate plasma processing that
is a variation of the system of FIG. 8, in accordance with one
embodiment of the present invention; and
[0025] FIG. 12 shows a method for substrate plasma processing, in
accordance with one embodiment of the present invention.
DETAILED DESCRIPTION
[0026] In the following description, numerous specific details are
set forth in order to provide a thorough understanding of the
present invention. It will be apparent, however, to one skilled in
the art that the present invention may be practiced without some or
all of these specific details. In other instances, well known
process operations have not been described in detail in order not
to unnecessarily obscure the present invention.
[0027] A hollow cathode plasma source is operated by creating an
electric field in a confined space within the hollow cathode. The
electric field excites a process gas supplied to the confined space
to transform the process gas into a plasma within the confined
space. The plasma is separated by a sheath from the surfaces of the
hollow cathode that surround the confined space. In one embodiment,
the electric field created within the hollow cathode is referred to
as a saddle electric field due to its shape. The electric field
within the hollow cathode creates pendulum electrons. The pendulum
electrons are born at a surface of the hollow cathode surrounding
the confined space, or in the sheath surrounding the plasma. The
electrons born at a surface of the hollow cathode or within the
sheath are accelerated to an opposing portion of the sheath,
whereby the electrons cause ionization of neutral constituents in
the process gas, creation of radical species within the process
gas, and/or generation of more "fast" electrons.
[0028] The electric field within the hollow cathode also confines
the plasma within the confined space of the hollow cathode, thereby
increasing the plasma density in the confined space. Hollow
cathodes provide an attractive means for generating high plasma
density, but can have a narrow range of operation with regard to
pressure, dimensions, and/or driving voltage. The present invention
provides hollow cathodes and associated methods of use that extend
the range of operation of the hollow cathodes to be suitable for
plasma etch processes in semiconductor fabrication, particularly at
advanced technology nodes, i.e., at smaller critical dimension
sizes within the integrated circuitry.
[0029] In various embodiments described herein, different arrays of
hollow cathodes are disclosed for use in plasma processing of a
substrate, e.g., semiconductor wafer. During operation, a process
gas is supplied to an array of hollow cathodes to generate plasma
within each hollow cathode in the array. Then, the reactive
constituents of the plasma are passed from the array of hollow
cathodes to a low pressure environment within which the substrate
is disposed, thereby allowing the reactive constituents to contact
and do work on the substrate. Additionally, in some embodiments,
the array of hollow cathodes are operated in a manner whereby ion
processing and radical processing of the substrate are decoupled
and independently controlled.
[0030] FIG. 1A shows a vertical cross-section of a hollow cathode
assembly 100, in accordance with one embodiment of the present
invention. In this example embodiment, the hollow cathode assembly
100 includes a hollow cylinder 101 of electrically conductive
material. The hollow cathode assembly 100 also includes
electrically conductive rings 103A, 103B disposed at each end of
the hollow cylinder 101. The electrically conductive rings 103A,
103B are separated from the hollow cylinder 101 by dielectric rings
105A, 105B, respectively. Also, in this example embodiment, each of
the electrically conductive rings 103A, 103B is electrically
connected to a reference ground potential 107.
[0031] Multiple radiofrequency (RF) power sources 109A, 109B are
connected to supply RF power to the hollow cylinder 101. More
specifically, each of the multiple RF power sources 109A, 109B is
connected to supply RF power through respective matching circuitry
111, to the hollow cylinder 101. The matching circuitry 111 is
defined to prevent/mitigate reflection of the RF power from the
hollow cylinder 101, such that the RF power will be transmitted
through the hollow cylinder 101 to the reference ground potential
107. It should be understood that although the example embodiment
of FIG. 1A shows two RF power sources 109A, 109B, other embodiments
can utilize more than two RF power sources.
[0032] During operation, a process gas is flowed through an
interior cavity of the hollow cathode assembly 100, as depicted by
arrows 113. Also, during operation, RF power supplied to the hollow
cylinder 101 from the multiple RF power sources 109A, 109B
transforms the process gas into a plasma 115 within the hollow
cylinder 101. In the plasma 115, the process gas is transformed to
include both ionized constituents and radical species which may be
capable of doing work on a substrate when exposed to the substrate.
It should be appreciated that more than one RF power source 109A,
109B is used to supply RF power to the hollow cathode assembly 100.
Each of the RF power sources 109A, 109B is independently
controllable with regard to RF power frequency and amplitude.
[0033] The plasma 115 is confined within the hollow cylinder 101 by
the electric field generated by the RF power supplied from the
multiple RF power sources 109A, 109B. Also, a sheath 117 is defined
within the hollow cylinder 101 about the plasma 115. FIG. 1B shows
a horizontal cross-section of the hollow cathode assembly 100
corresponding to View A-A identified in FIG. 1A, in accordance with
one embodiment of the present invention. As shown in FIG. 1B, the
sheath 117 separates the plasma 115 from the interior surface of
the hollow cylinder 101.
[0034] In contrast to the hollow cathode assembly 100 of FIGS.
1A-1B, conventional hollow cathode sources have been powered by
either a single RF power source or by a direct current (DC) power
source, but not both. Therefore, the operating range of the
conventional hollow cathode source with regard to process gas
pressure has been determined by a single power source and the
particular configuration/dimensions of the hollow cathode
source.
[0035] FIG. 2A shows a plasma density versus process gas pressure
curve 201 for a hollow cathode of a given configuration and
dimensions operating at either a single RF frequency or at DC. As
shown in FIG. 2A, an optimal process gas pressure 203 corresponds
to a peak plasma density. The plasma density falls as the process
gas pressure is moved in either direction from the optimal process
gas pressure 203. Therefore, at either the single RF frequency or
DC, the hollow cathode of fixed configuration and dimensions is
required to operate within a narrow process gas pressure range
about the optimal process gas pressure 203. This narrow process gas
pressure range can have limited usefulness in semiconductor
fabrication processes that require a broader operational process
gas pressure range.
[0036] FIG. 2B shows a plasma density versus process gas pressure
curve 209 for the hollow cathode assembly 100 of FIGS. 1A-1B, in
accordance with one embodiment of the present invention. The curve
209 includes a first component curve 205 corresponding to the first
RF power source 109A, and a second component curve 207
corresponding to the second RF power source 109B. The first RF
power source 109A generates a peak plasma density within a process
gas pressure range about a first optimal process gas pressure 206.
The second RF power source 109B generates a peak plasma density
within a process gas pressure range about a second optimal process
gas pressure 208. Because the second optimal process gas pressure
208 associated with the second RF power source 109B is greater than
the first optimal gas pressure 206 associated with the first RF
power source 109A, the effective plasma density versus process gas
pressure curve 209 exhibits a broader effective pressure range 211
than what is achievable with either of the RF power sources 109A,
109B alone.
[0037] Therefore, it should be understood that use of multiple
independent RF power sources at appropriate frequencies to power a
hollow cathode can extend the operational range of the hollow
cathode well beyond what is achievable with use of either a single
RF frequency power source or DC power source. In following, use of
multiple independent RF power sources at appropriate frequencies
with an appropriately configured hollow cathode assembly can extend
the effective process gas operational pressure range of the hollow
cathode assembly, and thereby enable use of the hollow cathode
assembly as a plasma source in semiconductor fabrication processes.
Moreover, for a given hollow cathode assembly configuration, use of
more than two RF power sources at different frequencies can
substantially increase the effective process gas operational
pressure range of the given hollow cathode assembly.
[0038] In one embodiment, two RF power frequencies are supplied to
the hollow cathode assembly 100. In one instance of this
embodiment, the two RF power frequencies are about 2 megaHertz
(MHz) and about 60 MHz. In another embodiment, three RF power
frequencies are supplied to the hollow cathode assembly 100. In one
instance of this embodiment, one of the three RF power frequencies
is within a range extending from about 100 kiloHertz (kHz) to about
2 MHz, and the other two RF power frequencies are about 27 MHz and
about 60 MHz. In this embodiment, the lowest frequency is used to
set up the hollow cathode effect. Also in this embodiment, the
highest frequency is used to establish the initial plasma with the
required sheath size. Also in this embodiment, the intermediate
frequency is used to bridge process regimes and aid in making the
plasma strike efficiently. This three RF power frequency embodiment
provides for hollow cathode plasma generation at process gas
pressures within a range extending from about one milliTorr (mTorr)
to hundreds of mTorr. The upper end of the process gas pressure
range (hundreds of mTorr) can be used for chamber cleaning
operations. The lower end of the process gas pressure range (about
one mTorr) can be used for plasma etching processes in advanced
gate and contact fabrication operations.
[0039] In various embodiments, the multiple RF power frequencies
supplied to the hollow cathode can be binned into five ranges. A
first of the five ranges is DC. A second of the five ranges is
referred to as a low range, and extends from hundreds of kHz to
about 5 kHz. A third of the five ranges is referred to as a medium
range, and extends from about 5 kHz to about 13 MHz. A fourth of
the five ranges is referred to as a high range, and extends from
about 13 MHz to about 40 MHz. A fifth of the five ranges is
referred to as a very high range, and extends from about 40 MHz to
more than 100 MHz. It should be understood that operation of the
hollow cathode with different RF power frequency combinations may
require different matching circuitry designs, various RF return
current path considerations, and use of different inter-electrode
dielectric material thicknesses.
[0040] With reference back to FIGS. 1A-1B, is should be understood
that the combination of the hollow cathode assembly 100 with the
multiple RF power sources 109A, 109B and their respective matching
circuitry 111, represent a hollow cathode system for plasma
generation in substrate plasma processing. In particular, the
hollow cylinder 101 represents an electrically conductive member
101 shaped to circumscribe an interior cavity 119. The electrically
conductive member 101 is formed to have a process gas inlet 121 in
fluid communication with the interior cavity 119. The electrically
conductive member 101 is also formed to have an opening 123 that
exposes the interior cavity 119 to a substrate processing
region.
[0041] The RF power source 109A represents a first RF power source
109A in electrical communication with the electrically conductive
member 101, so as to enable transmission of a first RF power to the
electrically conductive member 101. The RF power source 109B
represents a second RF power source 109A in electrical
communication with the electrically conductive member 101, so as to
enable transmission of a second RF power to the electrically
conductive member 101. The first and second RF power sources 109A,
109B are independently controllable, such that the first and second
RF powers are independently controllable with regard to frequency
and amplitude.
[0042] Further with regard to FIGS. 1A-1B, the electrically
conductive ring 103A represents a first electrically grounded
member 103A formed to circumscribe the process gas inlet 121. Also,
the dielectric ring 105A represents a first dielectric spacer 105A
formed to circumscribe the process gas inlet 121. The first
dielectric spacer 105A is disposed between the first electrically
grounded member 103A and the electrically conductive member 101.
Similarly, the electrically conductive ring 103B represents a
second electrically grounded member 103B formed to circumscribe the
opening 123 that exposes the interior cavity 119 to the substrate
processing region. Also, the dielectric ring 105B represents a
second dielectric spacer 105B formed to circumscribe the opening
123 that exposes the interior cavity 119 to the substrate
processing region. The second dielectric spacer 105B is disposed
between the second electrically grounded member 103B and the
electrically conductive member 101.
[0043] The matching circuitry 111 includes a first matching circuit
connected between the first RF power source 109A and the
electrically conductive member 101. The first matching circuit is
defined to prevent reflection of the first RF power from the
electrically conductive member 101. Also, the matching circuitry
111 includes a second matching circuit connected between the second
RF power source 109B and the electrically conductive member 101.
The second matching circuit is defined to prevent reflection of the
second RF power from the electrically conductive member 101. In
various embodiments, the hollow cathode system of FIGS. 1A-1B can
include one or more additional RF power sources in electrical
communication with the electrically conductive member 101, so as to
enable transmission of additional corresponding RF powers to the
electrically conductive member 101. The additional RF power sources
are independently controllable with regard to frequency and
amplitude.
[0044] While the hollow cylinder 101 represents the electrically
conductive member in the example embodiment of FIGS. 1A-1B, it
should be understood that the electrically conductive member of the
hollow cathode system can be shaped differently in other
embodiments. FIGS. 3A-3B show an electrically conductive member 300
of a hollow cathode system that is formed in multiple parts, in
accordance with one embodiment of the present invention. The
electrically conductive member 300 includes a central solid
cylinder 301, and an outer hollow cylinder 303, concentrically
disposed with respect to each other. The central solid cylinder 301
and the outer hollow cylinder 303 are sized such that an interior
cavity 305 is formed between the central solid cylinder 301 and the
outer hollow cylinder 303.
[0045] As shown in FIG. 3B, the process gas flows through a process
gas inlet 307 in fluid communication with the interior cavity 305,
as indicated by arrows 309. Also, the electrically conductive
member 300 is formed to have an opening 311 that exposes the
interior cavity 305 to a substrate processing region. A plasma is
generated within the interior cavity 305 of the electrically
conductive member 300, such that reactive species and ions of the
plasma can move from the interior cavity 305 through the opening
311 into the substrate processing region, as indicated by arrows
313.
[0046] In one embodiment, the first RF power source 109A is in
electrical communication with the central solid cylinder 301,
through appropriate matching circuitry 111. Also, in this
embodiment, the second RF power source 109B is in electrical
communication with the outer hollow cylinder 303, through
appropriate matching circuitry 111. In another embodiment, both the
first and second RF power sources 109A, 109B are in electrical
communication with each of the central solid cylinder 301 and the
outer hollow cylinder 303, through respective and appropriate
matching circuitry 111.
[0047] FIGS. 4A-4B show an electrically conductive member 400 of a
hollow cathode system that is formed in multiple parts, so as to
segment an interior cavity into multiple interior cavities 405A,
405B, in accordance with one embodiment of the present invention.
The electrically conductive member includes a central hollow
cylinder 401 and an outer hollow cylinder 403 disposed in a
concentric and spaced apart manner with respect to each other. The
first interior cavity 405A is formed within the central hollow
cylinder 401. The second interior cavity 405B is formed between the
central hollow cylinder 401 and the outer hollow cylinder 403.
[0048] As shown in FIG. 4B, the process gas flows through a first
process gas inlet 407A in fluid communication with the first
interior cavity 405A, as indicated by arrow 409A. Also, the process
gas flows through a second process gas inlet 407B in fluid
communication with the second interior cavity 405B, as indicated by
arrow 409B. The electrically conductive member 400 is further
defined to have an opening 411A that exposes the first interior
cavity 405A to a substrate processing region. Also, the
electrically conductive member 400 is defined to have an opening
411B that exposes the second interior cavity 405B to the substrate
processing region. A plasma is generated within the interior
cavities 405A, 405B of the electrically conductive member 400, such
that reactive species and ions of the plasma can move from the
interior cavities 405A, 405B through their respective openings
411A, 411B, into the substrate processing region, as indicated by
arrows 413A, 413B.
[0049] In one embodiment, the first RF power source 109A is in
electrical communication with the central hollow cylinder 401,
through appropriate matching circuitry 111. Also, in this
embodiment, the second RF power source 109B is in electrical
communication with the outer hollow cylinder 403, through
appropriate matching circuitry 111. In another embodiment, both the
first and second RF power sources 109A, 109B are in electrical
communication with the central hollow cylinder 401, through
appropriate matching circuitry 111. Also, in this embodiment, the
second RF power source 109B is in electrical communication with the
outer hollow cylinder 403, through appropriate matching circuitry
111. In yet another embodiment, both the first and second RF power
sources 109A, 109B are in electrical communication with each of the
central hollow cylinder 401 and the outer hollow cylinder 403.
[0050] In one embodiment, the first process gas inlet 407A of the
first interior cavity 405A is in fluid communication with a first
process gas source, and the second process gas inlet 407B of the
second interior cavity 405B is in fluid communication with a second
process gas source. In one version of this embodiment, the process
gas inlets 407A, 407B of both the first and second interior
cavities 405A, 405B are in fluid communication with a common
process gas source. In another version of this embodiment, the
first and second process gas sources are independently controllable
with regard to process gas type, process gas pressure, process gas
flow rate, process gas temperature, or any combination thereof
[0051] In the embodiment of FIGS. 4A-4B, at least one of the
central and outer hollow cylinders 401, 403 that is to be exposed
to a higher pressure process gas within either of the interior
cavities 405A, 405B is connected to a lower frequency one of the at
least two independently controllable RF power sources 109A, 109B.
Also, in this embodiment, at least one of the central and outer
hollow cylinders 401, 403 that is to be exposed to a lower pressure
process gas within the interior cavities 405A, 405B is connected to
a higher frequency one of the at least two independently
controllable RF power sources 109A, 109B.
[0052] FIG. 5 shows a vertical cross-section through a
multi-frequency RF powered hollow cathode 500, in which an interior
cavity 505 of the hollow cathode 500 is shaped to affect process
gas pressure, in accordance with one embodiment of the present
invention. In the example embodiment of FIG. 5, the hollow cathode
500 includes a first electrically conductive member 501, and a
second electrically conductive member 503, positioned in a
sequential manner relative to a process gas flow path through the
hollow cathode 500, as indicated by arrows 509. The first and
second electrically conductive member 501, 503 are separated from
each other by a dielectric material 504. A portion of the interior
cavity 505 extending through the first electrically conductive
member 501 is of smaller size to maintain a higher process gas
pressure therein. However, a portion of the interior cavity 505
extending through the second electrically conductive member 503 is
diffuser-shaped so as to reduce the process gas pressure
therein.
[0053] Because higher process gas pressures require lower frequency
RF power to generate an optimum plasma density, vice-versa, the
first electrically conductive member 501 having the smaller sized
portion of the interior cavity 505 may be connected to a lower
frequency one of the RF power sources 109A, 109B. In a
complementary manner, the second electrically conductive member 503
having the diffuser-shaped portion of the interior cavity 505 may
be connected to a higher frequency one of the RF power sources
109A, 109B.
[0054] FIGS. 6A-6D show examples of multi-frequency RF powered
hollow cathodes 600A-600D in which electrically conductive members
are positioned in a sequential manner relative to a process gas
flow path, as indicated by arrow 609. In various embodiments, the
hollow cathodes 600A-600D include a stack of multiple electrically
conductive cathode plates 601 separated from each other by
dielectric sheets 603. Holes are formed through the stack of
electrically conductive cathode plates 601 and dielectric sheets
603 to form the interior cavities of the hollow cathodes 600A-600D
through which the process gas flows, as indicated by arrows 609. It
should be understood that each of FIGS. 6A-6D shows a vertical
cross-section through one of multiple hollow cathodes formed within
a corresponding stack of electrically conductive cathode plates 601
and dielectric sheets 603.
[0055] In the example embodiments of FIGS. 6A-6D, each of the
multiple cathode plates 601 is connected to receive RF power from
one or more of at least two independently controllable RF power
sources 109A, 109B, through appropriate matching circuitry 111. The
process gas within the interior cavities 605A-605D of the hollow
cathodes 600A-600D is transformed into plasma by the RF power
emitted from the cathode plates 601.
[0056] FIG. 6A shows the example hollow cathode 600A in which three
electrically conductive cathode plates 601 are disposed and
separated from each other by dielectric sheets 603, in accordance
with one embodiment of the present invention. In FIG. 6A, two
independently controlled RF power sources 109A, 109B are used to
supply RF power to the cathode plates 601 at two different
frequencies F1, F2, e.g., at a low frequency F1 and at a high
frequency F2, vice-versa. The embodiment of FIG. 6A also includes
an upper ground plate 650A and a lower ground plate 650B, to
provide return paths for the RF power emitted from the cathode
plates 601. The ground plates 650A, 650B are separated from their
neighboring cathode plates 601 by dielectric sheets 603. Also, the
ground plates 650A, 605B have holes formed therein to match the
holes formed within the cathode plates 601 and dielectric sheets
603.
[0057] It should be understood that not all embodiments are
required to include upper and lower ground plates 650A, 605B. For
instance, other structures within a plasma processing chamber
around the hollow cathodes may provide a suitable RF power return
path. For example, FIG. 6B shows the example hollow cathode 600B,
as a variation of the hollow cathode 600A of FIG. 6A, in which the
lower ground plate 650B is absent, in accordance with one
embodiment of the present invention. FIG. 6C shows the example
hollow cathode 600C, as a variation of the hollow cathode 600A of
FIG. 6A, in which three independently controlled RF power sources
109A, 109B, 109C are used to supply RF power to the cathode plates
601 at three different frequencies F1, F2, F3, i.e., at the low
frequency F1, at a medium frequency F3, and at the high frequency
F2, in accordance with one embodiment of the present invention.
[0058] FIG. 6D shows the example hollow cathode 600D in which four
electrically conductive cathode plates 601 are disposed and
separated from each other by dielectric sheets 603, in accordance
with one embodiment of the present invention. In FIG. 6D, three
independently controlled RF power sources 109A, 109B, 109C are used
to supply RF power to the cathode plates 601 at three different
frequencies F1, F2, F3, i.e., at the low frequency F1, at the
medium frequency F3, and at the high frequency F2. It should be
understood that the hollow cathode configurations of FIGS. 6A-6D
are provided way of example, and do not represent an exhaustive set
of possible hollow cathode configurations. In other embodiments,
hollow cathodes can be formed in a manner similar to those depicted
in FIGS. 6A-6D, but may include a different number of cathode
plates 601, may utilize a different number of RF power frequencies,
and may or may not utilize upper and/or lower ground plates 650A,
650B.
[0059] Additionally, in some embodiments, multiple RF power
frequencies can be applied to a single cathode plate 601. For
example, in a hollow cathode that includes multiple cathode plates
601, one or more of the multiple cathode plates 601 may be
individually connected to receive multiple RF power frequencies.
FIG. 6E shows an example hollow cathode 600E in which a single
electrically conductive cathode plate 601 is connected to receive
multiple RF power frequencies F1, F2, etc., in accordance with one
embodiment of the present invention. FIG. 6E also shows how the
cathode plate 601 can be defined to include a shaped interior
cavity 605E to affect process gas flow and/or pressure. It should
be understood that the holes formed through the cathode plates 601,
in the example embodiments of FIGS. 6A-6E, can be defined in many
different ways to influence process gas flow a and/or pressure
variation along the process gas flow paths through the hollow
cathodes.
[0060] FIG. 7 shows a hollow cathode system 700 for plasma
generation in substrate plasma processing, in accordance with one
embodiment of the present invention. The hollow cathode system
includes a plurality of electrically conductive plates 701, 750A,
750B stacked in a layered manner. The hollow cathode system 700
also includes dielectric sheets 703 disposed between each
adjacently positioned pair of the plurality of electrically
conductive plates 701, 750A, 750B. A number of holes 707 are formed
to extend through the plurality of electrically conductive plates
701, 750A, 750B and dielectric sheets 703 disposed there between.
Each hole 707 forms an interior cavity of a hollow cathode. More
specifically, the portion of each hole 707 that passes through an
RF powered electrically conductive plate 701 forms an interior
cavity of a hollow cathode.
[0061] In the hollow cathode system 700, at least two independently
controllable RF power sources 109A, 109B are electrically connected
to the electrically conductive plate 701. Each of the at least two
independently controllable RF power sources 109A, 109B is
independently controllable with regard to RF power frequency and
amplitude. In the example embodiment of FIG. 7, the hollow cathode
system 700 includes a top ground plate 750A, a central cathode
plate 701 connected to receive RF power from each of the at least
two independently controllable RF power sources 109A, 109B, and a
bottom ground plate 750B. It should be understood that in other
embodiments, the hollow cathode system 700 can include multiple RF
powered electrically conductive plates, such as described with
regard to FIGS. 6A-6D. Also, in other embodiments, the hollow
cathode system 700 may include only the top ground plate 750A, only
the bottom ground plate 750B, or neither the top nor bottom ground
plates 750A, 750B.
[0062] When deployed in a plasma processing system, a first end of
each of the number of holes 707 is in fluid communication with a
process gas source. And, a second end of each of the number of
holes 707 is in fluid communication with a substrate processing
region. In this manner the process gas flows through holes 707, as
indicated by arrows 709. As the process gas flows through the holes
707, RF powers emitted from the central cathode plate 701
transforms the process gas into plasma 710 within each hole 707. It
should be understood that a pressure of the process gas within the
hole 707 may suitable for plasma production within an RF power
frequency range corresponding to less than all of the at least two
independently controllable RF power sources 109A, 109B. However, as
long as at least one of the RF power sources 109A, 109B is operated
at a frequency suitable for plasma production with the supplied
process gas pressure, the other RF power frequencies can be
utilized to influence the plasma characteristics, i.e., the ion
and/or radical generation within the plasma.
[0063] FIG. 8 shows a system 800 for substrate plasma processing,
in accordance with one embodiment of the present invention. The
system 800 includes a chamber 801 formed by surrounding walls 801A,
a top plate 801B, and a bottom plate 801C. In various embodiments,
the chamber walls 801A, top plate 801B, and bottom plate 801C can
be formed from different materials, such as stainless steel or
aluminum, by way of example, so long as the chamber 801 materials
are structurally capable of withstanding pressure differentials and
temperatures to which they will be exposed during plasma
processing, and are chemically compatible with the plasma
processing environment.
[0064] The system 800 also includes a substrate support 803
disposed within the chamber 801. The substrate support 803 is
defined to hold a substrate 802 thereon during performance of a
plasma processing operation on the substrate. In the embodiment of
FIG. 8, the substrate support 803 is held by a cantilevered at n
affixed to a wall 801A of the chamber 801. However, in other
embodiments, the substrate support 803 can be affixed to the bottom
plate 801C of the chamber 801 or to another member disposed within
the chamber 801. In various embodiments, the substrate support 803
can be formed from different materials, such as stainless steel,
aluminum, or ceramic, by way of example, so long as the substrate
support 803 material is structurally capable of withstanding
pressure differentials and temperatures to which it will be exposed
during plasma processing, and is chemically compatible with the
plasma processing environment.
[0065] In one embodiment, the substrate support 803 includes a bias
electrode 807 for generating an electric field to attract ions
toward the substrate support 803, and thereby toward the substrate
802 held on the substrate support 803. Also, in one embodiment, the
substrate support 803 includes a number of cooling channels 809
through which a cooling fluid can be flowed during plasma
processing operations to maintain temperature control of the
substrate 802. Also, in one embodiment, the substrate support 803
can include a number of lifting pins 811 defined to lift and lower
the substrate 802 relative to the substrate support 803. In one
embodiment, a door assembly 813 is disposed within the chamber wall
801A to enable insertion and removal of the substrate 802 into/from
the chamber 801. Additionally, in one embodiment, the substrate
support 803 is defined as an electrostatic chuck equipped to
generate an electrostatic field for holding the substrate 802
securely on the substrate support 803 during plasma processing
operations.
[0066] The system 800 further includes a hollow cathode assembly
815 disposed within the chamber 801 above and spaced apart from the
substrate support 803, so as to be positioned above and spaced
apart from the substrate 802 when positioned on the substrate
support 803. A substrate processing region 817 exists between the
hollow cathode assembly 815 and the substrate support 803, so as to
exist over the substrate 802 when positioned on the substrate
support 803. In one embodiment, a vertical distance as measured
perpendicularly between the hollow cathode assembly 815 and the
substrate support 803, i.e., process gap, is within a range
extending from about 1 centimeter (cm) to about 10 cm. In one
embodiment, the vertical distance as measured perpendicularly
between the hollow cathode assembly 815 and the substrate support
803 is about 5 cm. Also, in one embodiment, a vertical position of
the substrate support 803 relative to the hollow cathode assembly
815, vice-versa, is adjustable either during performance of the
plasma processing operation or between plasma processing
operations.
[0067] The system 800 further includes a process gas source 819 in
fluid communication with the hollow cathode assembly 815, to supply
process gas to the hollow cathode assembly 815. In the example
embodiment of FIG. 8, a process gas plenum 821 is formed within the
chamber 801 above the hollow cathode assembly 815. The process gas
plenum 821 is in fluid communication with both the process gas
source 819 and each of multiple hollow cathodes 823 within the
hollow cathode assembly 815. The process gas plenum 821 is formed
to distribute the process gas to each of the multiple hollow
cathodes 823 within the hollow cathode assembly 815 in a
substantially uniform manner.
[0068] The system 800 also includes a plurality of RF power sources
109A, 109B in electrical communication with the hollow cathode
assembly 815. Each of the plurality of RF power sources 109A, 109B
is independently controllable with regard to RF power frequency and
amplitude. Also, RF power is transmitted from each of the RF power
sources 109A, 109B through respective matching circuitry 111 to
ensure efficient RF power transmission through the hollow cathode
assembly 815. During operation of the system 800, a plurality of RF
powers are respectively transmitted from the plurality of RF power
sources 109A, 109B to the hollow cathode assembly 815. The process
gas is transformed into a plasma within each of the multiple hollow
cathodes 823 of the hollow cathode assembly 815. Reactive species
825 within the plasma move from the hollow cathode assembly 815 to
the substrate processing region 817 over the substrate support 803,
i.e., onto the substrate 802 when disposed on the substrate support
803.
[0069] In one embodiment, upon entering the substrate processing
region 817 from the hollow cathode assembly 815, the used process
gas flows through peripheral vents 827, and is pumped out through
exhaust ports 829 by an exhaust pump 831. In one embodiment, a flow
throttling device 833 is provided to control a flow rate of the
used process gas from the substrate processing region 817. In one
embodiment, the flow throttling device 833 is defined as a ring
structure that is movable toward and away from the peripheral vents
827, as indicated by arrows 835.
[0070] The hollow cathode assembly 815 is defined over an area of
the substrate support 803 upon which the substrate 802 is to be
received for plasma processing. The multiple hollow cathodes 823 of
the hollow cathode assembly 815 are defined in exposure to the
substrate processing region 817. The multiple hollow cathodes 823
are distributed in a substantially uniform manner relative to the
area of the substrate support 803 upon which the substrate 802 is
to be received for plasma processing. In one embodiment, about 100
hollow cathodes 823 are distributed in a substantially uniform
manner relative to the area of the substrate support 803 upon which
the substrate 802 is to be received for plasma processing. However,
it should be understood that other embodiments may utilize more or
less hollow cathodes 823. In the example embodiment of FIG. 8, the
hollow cathode assembly 815 is essentially equivalent to the hollow
cathode system 700 described with regard to FIG. 7. However, it
should be appreciated that many different variations of the hollow
cathode assembly 815 can be implemented within the system 800 of
FIG. 8, such as those previously discussed with regard to FIGS. 1A
through 6E.
[0071] FIG. 9A shows another system 900A for substrate plasma
processing, in accordance with one embodiment of the present
invention. The system 900A is essentially equivalent to the system
800 of FIG. 8 with regard to the chamber 801, the substrate support
803, the peripheral vents 827, flow throttling device 833, exhaust
ports 829, and exhaust pump 831. However, the system 900A includes
a hollow cathode assembly 901 that is different from the hollow
cathode assembly 815 of system 800. Specifically, the hollow
cathode assembly 901 is formed to include process gas distribution
channels (interior to the hollow cathode assembly 901) in fluid
communication with a process gas supply line 903. The process gas
supply line 903 is connected in fluid communication between the
process gas source 819 and the hollow cathode assembly 901. The
process gas distribution channels within the hollow cathode
assembly 901 are formed to direct the process gas from the process
gas supply line 903 to each of multiple hollow cathodes 905 formed
within the hollow cathode assembly 901, in a substantially uniform
manner.
[0072] The system 900A further includes an exhaust plenum 907
formed within the chamber 801 above the hollow cathode assembly
901. The exhaust plenum 907 is fluidly connected to an exhaust pump
909. The hollow cathode assembly 901 includes multiple exhaust
holes 911 formed to extend completely through the hollow cathode
assembly 901 from the substrate processing region 817 to the
exhaust plenum 907. The multiple exhaust holes 911 are distributed
in a substantially uniform manner relative to the area of the
substrate support 803 upon which the substrate 802 is to be
received for plasma processing. Also, each of the multiple exhaust
holes 911 is isolated from the multiple hollow cathodes 905 and the
process gas distribution channels within the hollow cathode
assembly 901. It should be appreciated that the vertical pump out
capability afforded by the multiple exhaust holes 911 within the
hollow cathode assembly 901 provides for improved control over
reactive species residence time on the substrate 802, as a function
of radial position on the substrate.
[0073] FIG. 9B shows a system 900B for subs rate plasma processing
that is a variation of the system 900A of FIG. 9A, in accordance
with one embodiment of the present invention. The system 900B does
not utilize the peripheral vents 827 and lower exhaust ports 829.
Rather, in the system 900B, during operation, the substrate
processing region 817 is fluidly sealed between the substrate
support 803 and hollow cathode assembly 901, such that the exhaust
from the substrate processing region 817 is required to travel
through the exhaust holes 911 of the hollow cathode assembly
901.
[0074] FIG. 10 shows a system 1000 for substrate plasma processing
that is a variation of the system 800 of FIG. 8, in accordance with
one embodiment of the present invention. In the system 1000, the
process gas plenum 821 is defined to accommodate an anode plate
1001. More specifically, the anode plate 1001 is disposed within
the process gas plenum 821 and over the hollow cathode assembly
815. The anode plate 1001 is electrically connected to a negative
bias 1005 so as to drive ions from the multiple hollow cathodes 823
into the substrate processing region 817. Also, in one embodiment,
the system 1000 includes a cathode plate 1003 disposed between the
hollow cathode assembly 815 and the substrate processing region
817. The cathode plate 1003 is electrically connected to a positive
bias 1007 to pull ions from the multiple hollow cathodes 823 into
the substrate processing region 817. It should be understood that
different embodiments may include the anode plate 1001 alone, the
cathode plate 1003 alone, or both the anode and cathode plates
1001, 1003.
[0075] FIG. 11 shows a system 1100 for substrate plasma processing
that is a variation of the system 800 of FIG. 8, in accordance with
one embodiment of the present invention. The system 1100 is defined
to have a source plasma region 1103, in place of the process gas
plenum 821 in the system 800. Specifically, the source plasma
region 1103 is formed within the chamber 801 above the hollow
cathode assembly 815. The source plasma region 1103 is in fluid
communication with both the process gas source 819 and each of the
multiple hollow cathodes 823 within the hollow cathode assembly
815. The system 1100 also includes a coil assembly 1101 disposed to
transform the process gas within the source plasma region 1103 into
a source plasma 1105. In the system 1100, the chamber 801 top plate
801B is modified to include a window 1107 that is suitable for
transmission of RF power from the coil assembly 1101 into the
source plasma region 1103. In one embodiment, the window 1107 is
formed from quartz. In another embodiment, the window 1107 is
formed from a ceramic material, such as silicon carbide. In the
system 1100, the source plasma 1105 drives secondary plasma
generation in each of the multiple hollow cathodes 823 within the
hollow cathode assembly 815, in a substantially uniform manner.
[0076] FIG. 12 shows a method for substrate plasma processing, in
accordance with one embodiment of the present invention. It should
be understood that the method of FIG. 12 can be implemented within
either of the plasma processing systems 800, 900A, 900B, 1000, 1100
of FIGS. 8-11, and with either of the hollow cathode embodiments
described with regard to FIGS. 1A-11. The method includes an
operation 1201 for disposing a substrate in exposure to a substrate
processing region. The method also includes an operation 1203 for
disposing multiple hollow cathodes in exposure to the substrate
processing region. In one embodiment, a number of the multiple
hollow cathodes is within a range extending from about 25 to about
100. The method also includes an operation 1205 for flowing a
process gas through the multiple hollow cathodes.
[0077] In an operation 1207, a plurality of RF powers are
transmitted to the multiple hollow cathodes. The plurality of RF
powers are independently controlled with regard to frequency and
amplitude, and include at least two different frequencies. Also, at
least one of the plurality of RF powers transforms the process gas
into a plasma as the process gas flows through the multiple hollow
cathodes. Reactive species within the plasma enter the substrate
processing region to do work on the substrate.
[0078] In one embodiment, the plurality of RF powers include two or
more frequencies from the group consisting of 2 megaHertz (MHz), 27
MHz, 60 MHz, and 200 kiloHertz (kHz). In other embodiments, the
plurality of RF powers include at least two different RF power
frequencies corresponding to one or more of a low range, medium
range, high range, and very high range. The low frequency range
extends from hundreds (100's) of kHz to about 5 kHz. The medium
range extends from about 5 kHz to about 13 MHz. The high range
extends from about 13 MHz to about 40 MHz. The very high range
extends from about 40 MHz to more than 100 MHz.
[0079] The method can further include an operation for controlling
a pressure of the process gas. In one embodiment, the pressure of
the process gas enables formation of the plasma by some of the
plurality of RF powers and does not enable formation of the plasma
by others of the plurality of RF powers. In one embodiment, the
pressure of the process gas is controlled within a range extending
from about 1 milliTorr (mTorr) to about 500 mTorr. The method can
also include an operation for setting a process gap distance, as
measured perpendicularly between the substrate and the multiple
hollow cathodes, within a range extending from about 1 cm to about
10 cm.
[0080] It should be appreciated that simultaneous use of multiple
RF power frequencies/amplitudes, in combination with the hollow
cathode embodiments described herein, can advantageously provide an
ability to preferentially control generation of different types of
reactive species within the plasma. For example, application of an
RF power within the above-mentioned low frequency range can be used
to promote generation of ions in the plasma. And, application of an
RF power within the above-mentioned high frequency range can be
used to promote generation of radicals in the plasma. In following,
application of multiple RF powers including a combination of low
and high frequencies at appropriate amplitudes can be used to
generate a particular mixture of ions and radicals in the plasma
that is suitable for a specific plasma processing operation.
[0081] Considering the foregoing, the method of FIG. 12 can include
an operation for controlling frequency and amplitude of a first set
of one or more RF powers of the plurality of RF powers so as to
promote generation of a first type of reactive species within the
plasma. The method can also include an operation for controlling
frequency and amplitude of a second set of one or more RF powers of
the plurality of RF powers so as to promote generation of a second
type of reactive species within the plasma. In one embodiment, the
first type of reactive species is ions, and the second type of
reactive species is radicals. In this embodiment, the frequency of
the first set of one or more RF powers is lower than the frequency
of the second set of one or more RF powers. For example, in one
embodiment, the frequency of the first set of one or more RF powers
can be within the above-mentioned low frequency range, and the
frequency of the second set of one or more RF powers can be within
the above-mentioned high frequency range.
[0082] Numerous multi-frequency RF powered hollow cathode
embodiments are disclosed herein that enable use of hollow cathode
systems at lower process gas pressures suitable for use in
semiconductor fabrication processes, such as plasma etching
processes. The hollow cathode structures disclosed herein can be
driven at high frequency, e.g., 60 MHz, and low frequency, e.g., 2
MHz or less, to provide for a sustained plasma within the hollow
cathodes at low pressure, while also generating high enough plasma
density. In this situation, the high frequency RF power component
can strike and drive the plasma, while the low frequency RF
component can provide for decreased plasma sheath size relative to
the hollow cathode interior cavity size. In this situation, the
saddle field of the hollow cathode may be parallel to the plane of
the hollow cathode electrode.
[0083] As discussed herein, in one embodiment, two or more RF power
frequencies can be used to drive a common electrode within the
hollow cathode assembly. In another embodiment, a high frequency RF
powered electrode can be sandwiched between low frequency RF
powered electrodes, such that a saddle field exists along an axis
of the hollow cathode interior cavity, when the low frequency RF
powered electrodes are operated in phase.
[0084] Some hollow cathodes may require higher process gas
pressures during operation. In this case, in one embodiment, a
hollow cathode array can be immersed between low frequency RF
powered electrodes driven either in phase or out of phase. In this
embodiment, the low frequency RF powered electrode provides a high
pressure environment above the lower pressure substrate processing
region. When driven in phase and close to the hollow cathode array,
the low frequency RF powered electrodes generate a saddle field
therebetween and along the axes of the hollow cathodes within the
hollow cathode array. When drive out of phase, i.e., in a push-pull
relationship, the low frequency RF powered electrodes generate a
saddle field on a side of the hollow cathode array facing the
instantaneous anode. This out of phase configuration can be
exploited to insert ions and electrons into the low pressure
substrate processing region.
[0085] In one embodiment, the hollow cathodes are configured to
include a pinch off point having low enough conductance to sustain
a pressure drop on the order of hundreds of mTorr at flow rates of
hundreds of sccm (standard cubic centimeter). The hollow cathodes
of this embodiment enable high pressure hollow cathode array
operation in conjunction with a low pressure substrate processing
region. In this embodiment, a high pressure side of the hollow
cathode, i.e., above the pinch point, is used to create a high
pressure hollow cathode. Also, the low pressure side of the hollow
cathode, i.e., below the pinch point, can be combined with an
electrostatic lens for ion or electron extraction from the hollow
cathode plasma.
[0086] It should be understood that many different configurations
of RF powered electrodes can be implemented within the
multi-frequency RF powered hollow cathodes disclosed herein. For
example, as disclosed herein with regard to FIGS. 6A-7, hollow
cathodes can be assembled in layers of conducting plates separated
by dielectric sheets, with arrays of holes formed therethrough.
Also, as disclosed in the example of FIGS. 3A-4B, the electrodes of
the hollow cathode can be concentrically defined, such that one
electrode is present within a hole of another electrode. Also, as
shown in the example of FIGS. 4A-4B, the electrodes of the hollow
cathode can form annuli for process gas flow.
[0087] Additionally, the hollow cathodes can include other shapes
not explicitly shown herein, or direct the flow of process gas
off-normal from the electrode surface of the hollow cathode. In
some embodiments, hollow cathodes can be placed in arrays of unit
cells, where electrodes having different frequency combinations are
disposed in close proximity to each other. Also, in some
embodiments, such as described with regard to FIGS. 3A-3B,
different regions of a hollow cathode can be arranged such that an
outer region is powered with a first set of RF power frequencies,
while an inner region is powered with a second set of RF power
frequencies, where the first and second sets of RF power
frequencies are different.
[0088] While this invention has been described in terms of several
embodiments, it will be appreciated that those skilled in the art
upon reading the preceding specification and studying the drawings
will realize various alterations, additions, permutations and
equivalents thereof. The present invention includes all such
alterations, additions, permutations, and equivalents as fall
within the true spirit and scope of the invention.
* * * * *