U.S. patent application number 09/829595 was filed with the patent office on 2001-09-06 for recessed coil for generating a plasma.
Invention is credited to Edelstein, Sergio, Forster, John C., Grunes, Howard, Stimson, Bradley O., Subramani, Anantha, Tepman, Avi, Xu, Zheng.
Application Number | 20010019016 09/829595 |
Document ID | / |
Family ID | 27095108 |
Filed Date | 2001-09-06 |
United States Patent
Application |
20010019016 |
Kind Code |
A1 |
Subramani, Anantha ; et
al. |
September 6, 2001 |
Recessed coil for generating a plasma
Abstract
A recessed coil for a plasma chamber in a semiconductor
fabrication system is provided. Recessing the coil reduces
deposition of material onto the coil which in turn leads to a
reduction in particulate matter shed by the coil onto the
workpiece.
Inventors: |
Subramani, Anantha; (San
Jose, CA) ; Forster, John C.; (San Francisco, CA)
; Stimson, Bradley O.; (San Jose, CA) ; Edelstein,
Sergio; (Los Gatos, CA) ; Grunes, Howard;
(Santa Cruz, CA) ; Tepman, Avi; (Cupertino,
CA) ; Xu, Zheng; (Foster City, CA) |
Correspondence
Address: |
KONRAD RAYNES & VICTOR, LLP
315 SOUTH BEVERLY DRIVE
SUITE 210
BEVERLY HILLS
CA
90212
US
|
Family ID: |
27095108 |
Appl. No.: |
09/829595 |
Filed: |
April 10, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09829595 |
Apr 10, 2001 |
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08853024 |
May 8, 1997 |
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6254746 |
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08853024 |
May 8, 1997 |
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08647182 |
May 9, 1996 |
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Current U.S.
Class: |
204/192.1 ;
204/192.12; 204/298.06; 204/298.08; 204/298.11 |
Current CPC
Class: |
H01J 37/32504 20130101;
H01J 37/32623 20130101; H01J 37/34 20130101; H01J 37/32651
20130101; H01J 37/321 20130101 |
Class at
Publication: |
204/192.1 ;
204/192.12; 204/298.08; 204/298.11; 204/298.06 |
International
Class: |
C23C 014/34 |
Claims
What is claimed is:
1. An apparatus for energizing a plasma within a semiconductor
fabrication system by coupling energy into the plasma, the
apparatus comprising: a semiconductor fabrication chamber having a
first wall, a second wall spaced inwardly of said chamber from said
first wall and a plasma containment region at least partially
defined by said first and second walls; and a coil supported on the
second wall in a position at least partially exposed to said plasma
containment region and positioned to couple energy into the plasma
containment region.
2. The apparatus of claim 1 further comprising a sputtering target
positioned at a boundary of the plasma containment region to define
a portion of the plasma containment region aligned about an axis
perpendicular with the target, said second wall being sufficiently
recessed in an outward direction from the first wall so that the
coil is positioned outside the plasma containment region portion
perpendicularly aligned with the target.
3. The apparatus of claim 2 further comprising a pedestal for
supporting a semiconductor workpiece positioned opposed to said
target across said plasma containment region to define a portion of
the plasma containment region perpendicularly aligned about the
pedestal, said second wall being sufficiently recessed in an
outward direction with respect to said plasma containment region
from the first wall so that the coil is positioned outside the
plasma containment region.
4. The apparatus of claim 3 further comprising a floor wall
positioned between the first and second walls and below the coil to
collect particulate matter generated from the surface of the
coil.
5. The apparatus of claim 1, further including a shield member
extending at least partially about said target to block access of
at least portions of said target to portions of said coil.
6. The apparatus of claim 4, further including a shield member
extending at least partially about said target to block access of
at least portions of said target to portions of said coil.
7. The apparatus of claim 1, further including a labyrinth member
extending between said coil and said second wall and spaced from
said second wall.
8. An apparatus for energizing a plasma within a semiconductor
fabrication chamber by coupling energy into the plasma, the
apparatus comprising: a generally annular-shaped shield wall; a
generally disk-shaped target positioned above the shield wall; and
an adapter ring positioned between the shield wall and the target
and having a recess therein exposed inwardly of the chamber, said
adapter ring having a coil positioned at least partially in said
recess and energizable by an a.c. source to couple energy into the
plasma containment region.
9. The apparatus of claim 8 wherein the adapter ring has a wall for
carrying the coil and forming a boundary of said recess, said
adapter wall being recessed in an outward direction relative to the
shield wall.
10. The apparatus of claim 9 wherein the adapter ring further
comprises a floor wall positioned below the coil to collect
particulate matter from the coil.
11. The apparatus of claim 10 wherein the adapter ring further
comprises a ceiling wall positioned above the coil to shield the
coil from at least a portion of the target.
12. An apparatus for energizing a plasma within a semiconductor
fabrication system by coupling energy into the plasma, the
apparatus comprising: a semiconductor fabrication chamber having a
shield wall and a plasma containment region within the wall; a coil
carried by the wall and positioned to couple energy into the plasma
containment region; a target positioned above the plasma
containment region; and a second shield wall positioned between the
target and the shield to shield the coil from at least a portion of
the target.
13. The apparatus of claim 12 wherein the coil is positioned
vertically underneath the second shield wall.
14. A standoff for supporting a coil in a semiconductor fabrication
system having a wall upon which deposition material is deposited,
comprising: a first base member adapted to be coupled to the wall;
and a first cover member adapted to be coupled to the coil, said
cover member being positioned over the base member, said cover
member and base member defining a passage between the base member
and the cover member, wherein at least one of the cover member and
the base member is made of an insulative material.
15. The standoff of claim 14 further comprising a second cover
member positioned to at least partially cover said first cover
member.
16. The standoff of claim 15 wherein said first and second cover
members are each cup-shaped.
17. The standoff of claim 15 wherein said second cover member
comprises a conductive metal.
18. The standoff of claim 17 wherein said second cover member is
biased at a potential level to inhibit sputtering of said second
cover member.
19. The standoff of claim 18 wherein said second cover member is
coupled to electrical ground.
20. The standoff of claim 15 wherein said second cover member is
spaced from said first cover member to define a passageway between
said first and second cover members.
21. The standoff of claim 14 further comprising a second base
member adapted to be coupled to said wall, and a fastener for
fastening said first and second base members to compress said wall
between said first and second base members.
22. The standoff of claim 21 wherein said first and second base
members each has a shoulder portion positioned to oppose said
shoulder portion of said other base member with a portion of said
wall between said shoulder portions of said first and second base
members.
23. The standoff of claim 22 wherein said wall has an opening and
one of said first and second base members has a collar portion
adapted to extend through said wall opening.
24. The standoff of claim 23 wherein said collar portion is spaced
from the other of said first and second base members.
25. The standoff of claim 24 wherein said first and second base
members are formed of an electrically insulative material.
26. The standoff of claim 25 wherein said first and second base
members are formed of a ceramic material.
27. The standoff of claim 21 further comprising a second cover
member positioned to at least partially cover said first cover
member wherein said fastener comprises a post and said wall, said
first and second cover members and said first and second base
members each has an opening aligned to receive said post so that
said post passes through said wall, said first and second cover
members and said first and second base member openings.
28. The standoff of claim 27 wherein said post is formed of a
conductive material and has a first end coupled to said coil and a
second end extending though said wall opening, said standoff
further comprising a third cover member positioned to cover at
least a portion of said post second end, said third cover member
being formed of an insulative material.
29. The standoff of claim 28 wherein said second base member has a
shoulder portion spaced from said wall and said third cover member
has a lip portion positioned between said wall and said second base
member shoulder portion to retain said third cover member on said
second base member.
30. The standoff of claim 27 wherein said coil defines an opening
adapted to receive said fastener and said fastener further
comprises a flange portion adapted to engage said coil.
31. The standoff of claim 30 wherein said fastener further
comprises a nut having a threaded portion and said flange portion
and said post has a threaded portion adapted to engage and retain
said nut threaded portion.
32. The standoff of claim 14 wherein said cover member and base
member are spaced to define a plurality of passages between said
base member and said cover member wherein said passages are angled
with respect to each other to retard the passage of deposition
material through said passages.
33. The standoff of claim 14 wherein the base member has an outer
periphery which defines a diameter and the cover member has an
inner periphery spaced from the outer periphery of the base member
by a first predetermined gap which defines a first of the plurality
of passages wherein the ratio of the base member diameter to the
predetermined gap is 14 or more.
34. The standoff of claim 33 wherein the first passageway has a
first predetermined length and the aspect ratio of the first
predetermined length to the first predetermined gap is 2 or
more.
35. The standoff of claim 14 wherein the base member has a front
face which defines a plurality of channels which are coupled to at
least one of the plurality of passageways to retard the passage of
deposition material through the passages.
36. The standoff of claim 35 wherein the base member has three
concentric channels in which the outermost channel has the greatest
width.
37. The standoff of claim 14 wherein the base member has a front
face and the cover member has a rear face and one of the base and
cover members has an insulative upstanding wall adjacent the center
of the member which spaces the base member front face from the
cover member rear face by a first predetermined gap which defines a
first of the plurality of passages having a first predetermined
length wherein the ratio of the first predetermined length to the
first predetermined gap is 6 or more.
38. A standoff for coupling RF current though an opening in a wall
to a coil in a semiconductor fabrication system, comprising: a
first conductive member adapted to extend through said wall
opening, said first conductive member having first and second ends,
said first end being positioned on a first side of said wall and
being adapted to be coupled to a source of RF current, and said
second end being positioned on a second side of said wall opposite
said first side of said wall and being adapted to be electrically
coupled to said coil; a first insulative base member adapted to
extend through said wall opening between said conductive member and
said wall to insulate said conductive member from said wall; and a
first cover member positioned to at least partially cover said base
member, said first cover member and base member defining a passage
between said first base member and said first cover member.
39. The standoff of claim 38 further comprising a second cover
member positioned to at least partially cover said first cover
member.
40. The standoff of claim 39 wherein said first and second cover
members are each cup-shaped.
41. The standoff of claim 39 wherein said second cover member
comprises a conductive metal.
42. The standoff of claim 41 wherein said second cover member is
biased at a potential level to inhibit sputtering of said second
cover member.
43. The standoff of claim 42 wherein said second cover member is
coupled to electrical ground.
44. The standoff of claim 39 wherein said second cover member is
spaced from said first cover member to define a passageway between
said first and second cover members.
45. The standoff of claim 38 further comprising a second conductive
member positioned on said first side of said wall and adapted to be
electrically coupled to said first conductive member, and a second
insulative base member adapted to be coupled to said wall between
said second conductive member and said wall to insulate said second
conductive member from said wall.
46. The standoff of claim 45 further comprising a first fastener
for fastening said first and second conductive members
together.
47. The standoff of claim 46 further comprising further a second
cover member positioned to at least partially cover said first
cover member and a second fastener for fastening said second cover
member to said wall.
48. The standoff of claim 47 wherein said second cover defines a
passageway coupled to said second fastener to vent said second
fastener.
49. The standoff of claim 45 wherein said first and second
conductive members each has a shoulder portion positioned to oppose
said shoulder portion of said other conductive member.
50. The standoff of claim 49 wherein said wall has an opening and
one of said first and second base members has a collar portion
adapted to extend through said wall opening.
51. The standoff of claim 50 wherein said portion is spaced said
other of said first and second base members.
52. The standoff of claim 51 wherein said first and second base
members are formed of an electrically insulative material.
53. The standoff of claim 38 wherein said first and second base
members are formed of a ceramic material.
54. The standoff of claim 45 further comprising a second cover
member positioned to at least partially cover said first cover
member wherein said fastener comprises a post and said wall, said
first and second cover members and said first and second base
members each has an opening aligned to receive said post so that
said post passes through said wall, said first and second cover
members and said first and second base member openings.
55. The standoff of claim 54 wherein said post is formed of a
conductive material and has a first end coupled to said coil and a
second end extending though said wall opening, said standoff
further comprising a third cover member positioned to cover at
least a portion of said post second end, said third cover member
being formed of an insulative material.
56. The standoff of claim 55 wherein said second base member has a
shoulder portion spaced from said wall and said third cover member
has a lip portion positioned between said wall and said second base
member shoulder portion to retain said third cover member on said
second base member.
57. The standoff of claim 54 wherein said coil defines an opening
adapted to receive said fastener and said fastener further
comprises a flange portion adapted to engage said coil.
58. The standoff of claim 57 wherein said fastener further
comprises a nut having a threaded portion and said flange portion,
and said post has a threaded portion adapted to engage and retain
said nut threaded portion.
59. The standoff of claim 14 wherein said cover member and base
member are spaced to define a plurality of passages between said
base member and said cover member wherein said passages are angled
with respect to each other to retard the passage of deposition
material through said passages.
60. The standoff of claim 14 wherein the base member has an outer
periphery which defines a diameter and the cover member has an
inner periphery spaced from the outer periphery of the base member
by a first predetermined gap which defines a first of the plurality
of passages wherein the ratio of the base member diameter to the
predetermined gap is 14 or more.
61. The standoff of claim 60 wherein the first passageway has a
first predetermined length and the aspect ratio of the first
predetermined length to the first predetermined gap is 2 or
more.
62. The standoff of claim 14 wherein the base member has a front
face which defines a plurality of channels which are coupled to at
least one of the plurality of passageways to retard the passage of
deposition material through the passages.
63. The standoff of claim 62 wherein the base member has three
concentric channels in which the outermost channel has the greatest
width.
64. The standoff of claim 14 wherein the base member has a front
face and the cover member has a rear face and one of the base and
cover members has an insulative upstanding wall adjacent the center
of the member which spaces the base member front face from the
cover member rear face by a first predetermined gap which defines a
first of the plurality of passages having a first predetermined
length wherein the ratio of the first predetermined length to the
first predetermined gap is 6 or more.
65. A method of supporting a coil in a semiconductor fabrication
system having a wall upon which deposition material is deposited,
comprising: positioning a base member on the wall; and positioning
a first cover member over the base member and supporting the coil,
said cover member and base member defining a plurality of passages
between the base member and the first cover member, wherein at
least one of the first cover member and the base member is made of
an insulative material.
66. The method of claim 65 wherein the passages are angled with
respect to each other to retard the passage of deposition material
through the passages.
67. The method of claim 65 wherein the base member has an outer
periphery which defines a diameter and the first cover member has
an inner periphery spaced from the outer periphery of the base
member by a first predetermined gap which defines a first of the
plurality of passages wherein the ratio of the base member diameter
to the predetermined gap is 14 or more.
68. The method of claim 67 wherein the first passageway has a first
predetermined length and the aspect ratio of the first
predetermined length to the first predetermined gap is 2 or
more.
69. The method of claim 65 wherein the base member has a front face
which defines a plurality of channels which are coupled to at least
one of the plurality of passageways to retard the passage of
deposition material through the passages.
70. The method of claim 69 wherein the base member has three
concentric channels in which the outermost channel has the greatest
width.
71. The method of claim 65 wherein the base member has a front face
and the first cover member has a rear face and one of the base and
first cover members has an insulative upstanding wall adjacent the
center of the member which spaces the base member front face from
the first cover member rear face by a first predetermined gap which
defines a first of the plurality of passages having a first
predetermined length wherein the ratio of the first predetermined
length to the first predetermined gap is 6 or more.
72. The method of claim 65 further comprising at least partially
covering said first cover member using a second cover member.
73. The method of claim 66 wherein said first and second cover
members are each cup-shaped.
74. The method of claim 66 wherein said second cover member
comprises a conductive metal.
75. The method of claim 66 further comprising biasing said second
cover member at a potential level to inhibit sputtering of said
second cover member.
76. The method of claim 75 wherein said second cover member is
coupled to electrical ground.
77. The method of claim 66 wherein said second cover member is
spaced from said first cover member to define a passageway between
said first and second cover members.
78. The method of claim 65 further comprising conducting RF current
through a first conductive member received in said insulative base
member.
79. The method of claim 78 further comprising conducting RF current
through a second conductive member positioned on one side of said
wall and adapted to be electrically coupled to said first
conductive member, and positioning a second insulative base member
between said second conductive member and said wall to insulate
said second conductive member from said wall.
80. The method of claim 79 further comprising fastening said first
and second conductive members together using a first fastener.
81. The method of claim 80 further comprising at least partially
covering said first cover member using a second cover member and
fastening said second cover member to said wall using a second
fastener.
82. The method of claim 81 further comprising venting said second
fastener using a passageway defined by said second cover.
Description
RELATED APPLICATIONS
[0001] This application is a continuation-in-part application of
copending application Ser. No. 08/647,182, entitled "Recessed Coil
for Generating a Plasma," filed May 9, 1996 (attorney docket No.
1186/PVD/DV).
FIELD OF THE INVENTION
[0002] The present invention relates to plasma generators, and more
particularly, to a method and apparatus for generating a plasma in
the fabrication of semiconductor devices.
BACKGROUND OF THE INVENTION
[0003] Radio frequency (RF) generated plasmas have become
convenient sources of energetic ions and activated atoms which can
be employed in a variety of semiconductor device fabrication
processes including surface treatments, depositions, and etching
processes. For example, to deposit materials onto a semiconductor
wafer using a sputter deposition process, a plasma is produced in
the vicinity of a sputter target material which is negatively
biased. Ions created within the plasma impact the surface of the
target to dislodge, i.e., "sputter" material from the target. The
sputtered materials are then transported and deposited on the
surface of the semiconductor wafer.
[0004] Sputtered material has a tendency to travel in straight line
paths from the target to the substrate being deposited at angles
which are oblique to the surface of the substrate. As a
consequence, materials deposited in etched trenches and holes of
semiconductor devices having trenches or holes with a high depth to
width aspect ratio, can bridge over causing undesirable cavities in
the deposition layer. To prevent such cavities, the sputtered
material can be "collimated" into substantially vertical paths
between the target and the substrate by negatively charging the
substrate or substrate support and positioning appropriate
vertically oriented collimating electric fields adjacent the
substrate if the sputtered material is sufficiently ionized by the
plasma. However, material sputtered by a low density plasma often
has an ionization degree of less than 1% which is usually
insufficient to avoid the formation of an excessive number of
cavities. Accordingly, it is desirable to increase the density of
the plasma to increase the ionization rate of the sputtered
material in order to decrease the formation degree of unwanted
cavities in the deposition layer. As used herein, the term "dense
plasma" is intended to refer to one that has a high electron and
ion density.
[0005] There are several known techniques for exciting a plasma
with RF fields including capacitive coupling, inductive coupling
and wave heating. In a standard inductively coupled plasma (ICP)
generator, RF current passing through a coil surrounding the plasma
induces electromagnetic currents in the plasma. These currents heat
the conducting plasma by ohmic heating, so that it is sustained in
steady state. As shown in U.S. Pat. No. 4,362,632, for example,
current through a coil is supplied by an RF generator coupled to
the coil through an impedance matching network, such that the coil
acts as the first windings of a transformer. The plasma acts as a
single turn second winding of a transformer.
[0006] In order to maximize the energy being coupled from the coil
to the plasma, it is desirable to position the coil as close as
possible to the plasma itself. At the same time, however, it is
also desirable to minimize the number of chamber fittings and other
parts exposed to the material being sputtered so as to facilitate
cleaning the interior of the chamber and to minimize the generation
of particles being shed from interior surfaces. These particles
shed from interior surfaces can fall on the wafer itself and
contaminate the product. Accordingly, many sputtering chambers have
a generally annular-shaped shield enclosing the plasma generation
area between the target and the pedestal supporting the wafer. The
shield provides a smooth gently curved surface which is relatively
easy to clean and protects the interior of the chamber from being
deposited with the sputtering material. In contrast, it is believed
by the present inventors that a coil and any supporting structure
for the coil would of necessity tend to have relatively sharply
curved surfaces which would be more difficult to clean away
deposited materials from the coil and its supporting structures. In
addition, it is believed that the smooth gently curved surface of
the shield would tend to shed fewer particles than the sharply
curved surfaces of the coil and its supporting structure.
[0007] Thus, on the one hand, it would be desirable to place the
coil outside the shield (as described in copending application Ser.
No. 08/559,345, filed Nov. 15,1995 for METHOD AND APPARATUS FOR
LAUNCHING A HELICON WAVE IN A PLASMA which is assigned to the
assignee of the present application and is incorporated herein by
reference) so that the coil is shielded from the material being
deposited. Such an arrangement would minimize generation of
particles by the coil and its supporting structure and would
facilitate cleaning of the chamber. On the other hand, it is
desirable to place the coil as close as possible to the plasma
generation area inside the shield to avoid any attenuation by the
spacing from the plasma or by the shield itself to thereby maximize
energy transfer from the coil to the plasma. Accordingly, it has
been difficult to increase energy transfer from the coil to the
plasma while at the same time minimizing particle generation and
facilitating chamber cleaning.
SUMMARY OF THE PREFERRED EMBODIMENTS
[0008] It is an object of the present invention to provide an
improved method and apparatus for generating plasmas within a
chamber, obviating, for practical purposes, the above-mentioned
limitations.
[0009] These and other objects and advantages are achieved by, in
accordance with one aspect of the invention, a plasma generating
apparatus which inductively couples electromagnetic energy from a
coil which is recessed with respect to the sputtering surface of a
target so as to minimize the deposition of target material onto the
coil. In addition, the coil is recessed with respect to the
perimeter of the pedestal (support member) and the deposition
surface of the workpiece supported on the pedestal such that any
target material deposited upon, and subsequently shed by, the coil
onto the workpiece is minimized. As a consequence, contamination of
the workpiece by particulate matter shed by the coil is
reduced.
[0010] In one embodiment, the coil is partially shielded from
deposition material by a dark space shield which is positioned
above the coil to prevent a substantial portion of the target
material from being deposited onto the coil. In an alternative
embodiment, the coil is carried by a separate adapter ring which
has a coil chamber to protect the coil from deposition material. In
addition, the coil chamber has a floor positioned below the coil to
catch particulate matter shed by the coil to reduce contamination
of the workpiece. Still further, the adapter ring coil chamber is
separate from the shield. As a consequence, the shield may be
separately cleaned or discarded thereby substantially facilitating
the cleaning of the shield and chamber and reducing the cost of the
shield itself.
[0011] In accordance with another aspect of the present invention,
the coil is carried on the shield or in the adapter ring chamber by
a plurality of novel coil standoffs and RF feedthrough standoffs
which have an internal labyrinth structure. As explained below, the
labyrinth structure permits repeated depositions of conductive
materials from the target onto the coil standoffs while preventing
the formation of a complete conducting path of deposited material
from the coil to the shield which could short the coil to the
shield which is typically at ground. In addition, the labyrinth
structure permits the standoff to have a low height which can
reduce the overall size of the chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a perspective, partial cross-sectional view of a
plasma generating chamber in accordance with one embodiment of the
present invention.
[0013] FIG. 2 is a partial cross-sectional view of the plasma
generating chamber of FIG. 1 shown installed in a vacuum
chamber.
[0014] FIG. 3 is a partial cross-sectional view of a plasma
generating chamber in accordance with another embodiment of the
present invention.
[0015] FIG. 4 is a cross-sectional view of a coil standoff of the
plasma generating chamber of FIG. 2.
[0016] FIG. 5 is a cross-sectional view of a coil feedthrough
standoff of the plasma generating chamber of FIG. 2.
[0017] FIG. 6 is a schematic diagram of the electrical
interconnections to the plasma generating chamber of FIG. 1.
[0018] FIG. 7 is a cross-sectional view of a coil standoff in
accordance with an alternative embodiment.
[0019] FIG. 8 is a cross-sectional view of a coil feedthrough
standoff in accordance with an alternative embodiment.
DETAILED DESCRIPTION OF THE DRAWINGS
[0020] Referring first to FIGS. 1 and 2, a plasma generator in
accordance with a first embodiment of the present invention
comprises a substantially cylindrical plasma chamber 100 which is
maintainable at vacuum and in this embodiment has a single helical
coil 104 which is carried internally of the chamber walls 108 by a
shield 106. The shield 106 protects the interior walls 108 (FIG. 2)
of the vacuum chamber 102 from the material being deposited within
the interior of the plasma chamber 100.
[0021] Radio frequency (RF) energy from an RF generator is radiated
from the coil 104 into the interior of the plasma chamber 100,
which energizes a plasma within the plasma containment region of
the plasma chamber 100. The energized plasma produces a plasma ion
flux which strikes a negatively biased target 110 positioned above
the plasma chamber 100. The plasma ions eject material from the
target 110, which may then be deposited onto a wafer or other
workpiece 112 supported by a pedestal 114 at the bottom of the
plasma chamber 100. As will be explained in greater detail below,
in accordance with one aspect of the present invention, the coil
104 is recessed with respect to the perimeter of the target 110 so
as to minimize the deposition of target material onto the coil 104.
In addition, the coil 104 is recessed with respect to the perimeter
of the chuck or pedestal 114 and the workpiece 112 supported on the
pedestal such that any target material subsequently shed by the
coil 104 onto the workpiece 112 is minimized. As a consequence,
contamination of the workpiece 112 by particulate matter shed by
the coil 104 is reduced.
[0022] In accordance with another aspect of the present invention,
the coil 104 is carried on the shield 106 by a plurality of novel
coil standoffs 120 which electrically insulate the coil 104 from
the supporting shield 106. As will be explained in greater detail
below, the insulating coil support standoffs 120 have an internal
labyrinth structure which permits repeated deposition of conductive
materials from the target 110 onto the coil standoffs 120 while
preventing the formation of a complete conducting path of deposited
material from the coil 104 to the shield 106 which could short the
coil 104 to the shield 106 (which is typically at ground).
[0023] To enable use of the coil as a circuit path, RF power must
be passed through the chamber walls and through the shield 106 to
opposite ends of the coil 104. Vacuum feedthroughs (not shown)
extend through the chamber wall to provide RF current from a
generator preferably located outside the chamber. Feedthroughs 124,
124a which pass RF current through the shield 106 need not be
vacuum feedthroughs, as both sides of shield 106 should be at the
same pressure. However, they do need to be protected from the
chamber environment, so as to prevent formation of a deposition
layer thereon which would create an electrical path from the coil
104 to the shield 106.
[0024] RF power is applied to the coil 104 by feedthroughs 122
which are supported by insulating feedthrough standoffs 124. The
feedthrough standoffs 124, like the coil standoffs 120, permit
repeated deposition of conductive material from the target onto the
feedthrough standoff 124 without the formation of a conducting path
which could short the coil 104 to the shield 106.
[0025] FIG. 2 shows the plasma chamber 100 installed in the vacuum
chamber 102 of a PVD (physical vapor deposition) system. Although
the plasma generator of the present invention is described in
connection with a PVD system for illustration purposes, it should
be appreciated that a plasma generator in accordance with the
present invention is suitable for use with all other semiconductor
fabrication processes utilizing a plasma including plasma etch,
chemical vapor deposition (CVD) and various surface treatment
processes.
[0026] As best seen in FIG. 2, the plasma chamber 100 has a dark
space shield ring 130 which provides a ground plane with respect to
the target 110 above which is negatively biased. In addition, the
shield ring 130 shields the outer edges of the target from the
plasma to reduce sputtering of the target outer edges. In
accordance with one aspect of the present invention, the dark space
shield 130 performs yet another function in that it is positioned
to shield the coil 104 (and the coil support standoffs 120 and
feedthrough standoffs 124) from the material being sputtered from
the target 110. The dark space shield 130 does not completely
shield the coil 104 and its associated supporting structure from
all of the material being sputtered since some of the sputtered
material travels at an oblique angle with respect to the vertical
axis of the plasma chamber 100. However, because much of the
sputtered material does travel parallel to the vertical axis of the
chamber or at relatively small oblique angles relative to the
vertical axis, the dark space shield 130 which is positioned in an
overlapping fashion above the coil 104, prevents a substantial
amount of sputtered material from being deposited on the coil 104.
By reducing the amount of material that would otherwise be
deposited on the coil 104, the generation of particles by the
material which is deposited on the coil 104 (and its supporting
structures) can be substantially reduced. In addition, the
lifetimes of these structures may be increased as well.
[0027] In the illustrated embodiment, the dark space shield 130 is
a closed continuous ring of titanium or stainless steel having a
generally inverted frusto-conical shape. It is recognized, of
course, that the dark space shield may be made from a variety of
other conductive materials and have other shapes which shield the
coil 104 and its associated supporting structures from at least
some of the material being deposited from the target. In the
illustrated embodiment, the dark space shield extends inward toward
the center of plasma chamber 100 so as to overlap the coil 104 by a
distance d of 1/4 inch. It is recognized, of course, that the
amount of overlap can be varied depending upon the relative size
and placement of the coil and other factors. For example, the
overlap may be increased to increase the shielding of the coil 104
from the sputtered material but increasing the overlap could also
further shield the target from the plasma which may undesirable in
some applications.
[0028] The chamber shield 106 is generally bowl-shaped and includes
a generally cylindrically shaped, vertically oriented wall 140 to
which the standoffs 120 and 124 are attached to insulatively
support the coil 104. The shield further has a generally
annular-shaped floor wall 142 which surrounds the chuck or pedestal
114 which supports the workpiece 112. A clamp ring 154 clamps the
wafer to the chuck 114 and covers the gap between the floor wall
142 of the shield 106 and the chuck 114. Thus, it is apparent from
FIG. 2 that the chamber shield 106 together with the clamp ring 154
protects the interior of the vacuum chamber 102 from the deposition
materials being deposited on the workpiece 112 in the plasma
chamber 100.
[0029] The vacuum chamber wall 108 has an upper annular flange 150.
The plasma chamber 100 is supported by an adapter ring assembly 152
which engages the vacuum chamber wall flange 150. The chamber
shield 106 has a horizontally extending outer flange member 160
which is fastened by a plurality of fastener screws (not shown) to
a horizontally extending flange member 162 of the adapter ring
assembly 152. The chamber shield 106 is grounded to the system
ground through the adapter ring assembly 152.
[0030] The dark space shield 130 also has an upper flange 170 which
is fastened to the horizontal flange 162 of the adapter ring
assembly 152. The dark space shield 130, like the chamber shield
106, is grounded through the adapter ring assembly 152.
[0031] The target 110 is generally disk-shaped and is also
supported by the adapter ring assembly 152. However, the target 110
is negatively biased and therefore should be insulated from the
adapter ring assembly 152 which is at ground. Accordingly, seated
in a circular channel formed in the underside of the target 110 is
a ceramic insulation ring assembly 172 which is also seated in a
corresponding channel 174 in the upper side of the target 152. The
insulator ring assembly 174 which may be made of a variety of
insulative materials including ceramics spaces the target 110 from
the adapter ring assembly 152 so that the target 110 may be
adequately negatively biased. The target, adapter and ceramic ring
assembly are provided with O-ring sealing surfaces (not shown) to
provide a vacuum tight assembly from the vacuum chamber flange 150
to the target 110.
[0032] FIG. 3 shows a recessed coil in accordance with an
alternative embodiment of the present invention in which the
generation of particulate matter by the coil is reduced by a
different structure to reduce contamination of the workpiece. In
the embodiment of FIG. 3, an adapter ring assembly 200 has been
modified to form a recessed coil chamber 202 which encloses a
helical coil 206 on three sides but exposes the coil 206 to the
plasma at an open fourth side of the recessed coil chamber 202. In
the illustrated embodiment, the recessed coil chamber 202 is
generally annular shaped and is defined by a generally cylindrical
vertical wall 210 which carries the coil 206 on insulative
standoffs (not shown) similar to the standoffs 120 and 124 of the
embodiment of FIGS. 1 and 2. The recessed coil chamber 202 further
has an upper ceiling wall 214 which performs a similar function to
that of the dark space shield 130 of the embodiment of FIGS. 1 and
2. More specifically, the coil chamber ceiling wall 214 provides a
ground plane with respect to the negatively biased target 110 and
also shields the periphery of the target 110 from the plasma. Still
further, the coil chamber ceiling wall 214 shields the coil 206 to
a limited extent from deposition material being ejected from the
target 110. The adapter ring assembly 200 is insulatively spaced
from the target 110 by an insulator ring assembly 216 between the
target 110 and the top surface of the chamber sealing wall 214 of
the adapter ring assembly 200.
[0033] In accordance with another aspect of the embodiment of FIG.
3, the coil chamber 202 of the adapter ring assembly 200 further
has a floor wall 220 which is positioned below the coil 206.
Because the coil 206 within the coil chamber 202 is recessed with
respect to the target 110, it is believed that the quantity of
target material which will be deposited upon the coil 206 (and its
supporting structures) will be reduced. However, to the extent
target materials are deposited on the coil 206, the coil chamber
floor wall 220 is positioned to catch much of any particulate
matter shed by the coil 206 such that the particulate matter
accumulates on the coil chamber floor wall 220 rather than on the
wafer or other workpiece. As a consequence, it is believed that
contamination of the workpiece will be further reduced.
[0034] The plasma chamber 190 of FIG. 3 has a bowl-shaped shield
230 which is similar to the shield 106 of the embodiment of FIGS. 1
and 2. However, in another aspect of the present invention, the
shield 230 is removably attached to a lower flange 232 of the
adapter ring assembly 200 by screws or other suitable fasteners.
Such an arrangement permits the shield 230 to be removed from the
adapter ring assembly 220 and separately cleaned and reattached to
the adapter ring assembly 200. Once the shield 230 has reached the
end of its useful life, it may be discarded and a new shield 230
attached to the adapter ring assembly 200.
[0035] Because the coil is not supported by the shield 230 in the
embodiment of FIG. 3, the surface of the shield 230 is more easily
cleaned because the shield surfaces are not interrupted by
standoffs for supporting the coil. Consequently, the usable life of
the shield 230 may be extended. In addition, the shield may be more
rapidly cleaned which can decrease downtime in which the processing
chamber is idled. Still further, because the shield 230 does not
have any coils or coils standoffs attached to it, the shield 230
may be more economically manufactured and therefore also more
economically discarded at the end of its useful life.
[0036] Conversely, coil chamber 202 of the adapter ring assembly
200, by protecting the coil from target deposition material, can
reduce the amount of cleaning necessary to remove deposited
material from the coil. This can also contribute to decreasing
downtime and increasing the lifetime of the coil, Furthermore,
because the coil chamber 202 of the adapter ring is more readily
separable from the shield 230, the coil 206 and coil chamber 202
need not be replaced when the shield 230 needs to be replaced.
Because shields tend to require replacement more frequently than
the coils, the cost of operation can be reduced by replacing the
coils 206 less frequently than the shields 230.
[0037] Turning now to FIG. 4, the internal structure of a coil
standoff 120 in accordance with another aspect of the present
invention is shown in greater detail. The coil standoff 120
includes a generally disk-shaped base member 250 which is
preferably made of an insulative dielectric material such as a
ceramic. Covering and shielding the base member 250 is a generally
cylindrically shaped cover member 252 which is preferably made of
the same material which is being deposited. Hence, if the material
being deposited is made of titanium, the cover member 252 is
preferably made of titanium as well. To facilitate adherence of the
deposited material (here for example, titanium), it is preferable
to treat the surface of the metal by bead blasting which will
reduce shedding of particles from the deposited material.
[0038] Affixed to the front of the cover member 252 is a generally
hook shaped bracket 254 of bead blasted titanium which receives and
supports a turn of the coil 104. The base member 250 is shown
attached to the wall 140 of the shield 106 by a bolt 251 or other
suitable fastener. (The base member 250 is attached to the wall 210
of the coil chamber 202 of the embodiment of FIG. 3 in a similar
manner.)
[0039] As set forth below, the base member 250 and the cover member
252 together define a labyrinth structure which inhibits the
formation of a conducting path across the standoff which could
short the coil to the shield (or the adapter ring of the embodiment
of FIG. 3). The base member 250 has an upstanding inner circular
wall 260 of sufficient height to space a top surface 262 of the
base member 250 from the inner surface 264 of the cover member 252
to define a gap G0. In addition, the outer diameter D1 of the base
member 250 is smaller than the inner diameter of the cover member
252 to define a gap G1 between the outer peripheral face 270 of the
base member 250 and the inner peripheral face 272 of the cover
member 252. Still further, the cover member 252 is sufficiently
thin so that the rear face 280 of the cover member 250 is spaced
from the wall 140 of the shield 106 so as to define another gap G2.
It is seen that the gaps G2, G1, G0 define a plurality of
passageways as represented by the arrow 290 between the cover
member 252 and the shield wall 140 and also between the cover
member 252 and the insulative base member 250. The arrow 290
represents the multi-angled path that deposition material would
have to take in order to coat the interior of the standoff 120. To
short the coil 104 to the shield wall 140, it would be necessary
for the deposition material to coat the interior of the standoff
120 to an extent such that a complete conductive path is provided
by the deposition material from the cover member 252 to the
insulative base member 250. To make such a complete conductive
path, the deposition material would have to bridge either the gap
G2 at the entrance to the interior of the standoff 120 or the gap
G1 or gap G0 of the internal passageways 290 unless the conductive
deposition material reached all the way to the innermost wall 260
of the insulative base member 250. If the conductive deposition
material coated the inner surfaces 264 and 272 of the cover member
252 and the surfaces 262 and 270 of the insulative member and
coated the inner wall 260 of the base member 250, a complete
conductive path could be formed from the coil 106 to the shield
wall 140.
[0040] To further retard such a complete conductive path from
forming, the front face 262 of the base member 250 has a plurality
of concentric channels 300a, 300b, 300c which are positioned to
accumulate conductive deposition material from the target to
prevent the deposition material from reaching the inner wall 260
and causing a short. The concentric channels may have varying
widths with the outer channels preferably having the greater width
so as to accumulate deposited material to prevent sufficient
material from accumulating adjacent the gap G0 which could bridge
the gap G0. It has been found that this labyrinth structure permits
the plasma chamber to be used for a relatively large number of
depositions of conductive metal without causing a short between the
coil and the shield. In addition, the overall thickness of the
standoff 120 is relatively thin. As a consequence, the overall
diameter of the plasma chamber can be made smaller because of the
reduced thickness of the standoffs.
[0041] In the illustrated embodiment, the insulative base member
250 has a diameter D1 of 1.50 inches and the gap G1 between the
outer periphery 270 of the base member 250 and the inner periphery
272 of the cover member 252 is 0.10 inches. It has been found that
the ratio of the diameter D1 of the insulative base member 252 to
the gap G1 between the outer periphery 270 of the base member 250
and the inner periphery 272 of the cover member 252 is preferably a
ratio of 14 or greater. The diameter to gap ratio of the
illustrated embodiment of FIG. 4 is 15.
[0042] Another ratio which has been found important in preventing
shorts through the standoffs is the ratio between the length L1 of
the passageway between the rear face 280 of the cover member 252
and the front face 262 of the insulative base member 250, to the
width of that passageway which is the gap G1. In the illustrated
embodiment, the length of the passageway L1 is 0.19 inches and the
gap G1 is 0.10 inches which provide an aspect ratio of 1.9 or
approximately 2. It has been found that an aspect ratio
substantially below 2 is not as effective in preventing shorts
through the standoff.
[0043] It is also desirable to reduce the width of the gap G0 to
retard the travel of deposition materials toward the inner wall
260. On the other hand, the gap G0 should not be made so narrow as
to facilitate the formation of a bridge of deposition material
across the gap G0 which could short the two sides of the gap
together. In the illustrated embodiment, a gap G0 of 0.05 inches
has been found satisfactory as noted above. In addition, the length
of travel L2 from the periphery 270 to the inner wall 260 of the
insulative base member 250 is 0.50 inches in the illustrated
embodiment. Thus, the aspect ratio of this portion of the
passageway is 0.5/0.05 or 10. It is believed that a lower aspect
ratio could undesirably increase the chances of a short
occurring.
[0044] As previously mentioned, the base member 250 has a plurality
of concentric channels 300a, 300b and 300c to accumulate deposition
material to prevent it from reaching the inner wall 260. In the
illustrated embodiment, the channels 300a, 300b and 300c have
widths of 0.10, 0.05 and 0.05, respectively. Increasing the number
and widths of these channels can further reduce the chance of a
short but such is likely to result in increasing the overall width
of the standoff which may not be acceptable for some applications.
Furthermore, to simplify manufacture, the number of channels can be
reduced to as few as one but such a simplified design may increase
the chance of a short. Here too, the gaps G0, G1 and G2 should be
chosen as discussed above to reduce the chances of a short.
[0045] FIG. 5 illustrates the coil feedthrough standoff 124 in
greater detail. The coil feedthrough standoff 124, like the coil
standoff 120 has a generally disk-shaped insulative base member 350
and a generally cylindrical cover member 352 of bead blasted
titanium which covers the insulative base member 350. However, the
feedthrough standoff 124 has a central aperture through which
extends a threaded conductive feedthrough bolt 356 through which RF
power is applied to the coil 104. The feedthrough bolt 356 is
received by a titanium sleeve 358 which has a termination sleeve
359 of bead blasted titanium which receives the coil 104. RF
current propagates along the surfaces of the sleeves 358 and 359 to
the coil 104. The feedthrough standoff 124 is secured to the wall
140 of the shield by the insulative base member on the interior
side of the wall 140 and a nut 366 threaded onto the feedthrough
bolt 356 on the other side of the wall 140. The nut 366 is spaced
from the wall 140 by a connector 368 and an insulative spacer 374.
The electrical connector 368 connects the feedthrough to an RF
generator (not shown) through a matching network (also not
shown).
[0046] The feedthrough standoff 124 also has an internal labyrinth
structure somewhat similar to that of the coil standoff 120 to
prevent the formation of a short between the coil 104 and the wall
140 of the shield. Here, the insulative base member 350 has a
diameter of D2 of 0.84 inches and a gap G3 of 0.06 inches between
the outer periphery 370 of the base member 350 and the inner
periphery 372 of the cover member 352. Hence, the ratio of the
diameter D2 to the gap G3 is 14, similar to the diameter to gap
ratio of 15 of the coil standoff 120 of FIG. 4. However, the aspect
ratio of the feedthrough standoff 124 of FIG. 5 is larger than the
aspect ratio of the coil standoff 120 of FIG. 4. Here, the length
L3 of the passageway between the outer periphery 370 of the
insulative base member 350 and the inner periphery 372 of the cover
member 352 is 0.27 inches. Hence, the aspect ratio of the length L3
to the gap G3 is 4.5. Consequently, the larger aspect ratio of the
embodiment of FIG. 5 may be more effective in preventing
undesirable shorts.
[0047] In the illustrated embodiment, a gap G4 of 0.04 inches
between the front face 362 of the base member 350 and the rear face
364 of the cover member 352 has been found satisfactory. In
addition, the length of travel L4 from the periphery 370 to the
inner wall 360 of the insulative base member 350 is 0.24 inches in
the illustrated embodiment. Thus, the aspect ratio of this portion
of the passageway 390 is 0.24/0.04 or 6. It is believed that a
lower aspect ratio could undesirably increase the chances of a
short occurring.
[0048] The base member 350, like the base member 250 has a
plurality of concentric channels 400a, and 400b to accumulate
deposition material to prevent it from reaching the inner wall 360.
In the illustrated embodiment, the channels 400a and 400 have
widths of 0.06 and 0.04 inches, respectively. The gap G5 between
the rear face 380 of the cover member 350 and the shield is 0.12
inches.
[0049] It should be recognized that other dimensions, shapes and
numbers of channels of the labyrinth are possible, depending upon
the particular application. Factors affecting the design of the
labyrinth include in addition to those discussed above, the type of
material being deposited and the number of depositions desired
before the standoffs need to be cleaned or replaced.
[0050] Each of the embodiments discussed above utilized a single
helical coil in the plasma chamber. It should be recognized that
the present invention is applicable to plasma chambers having more
than one coil. For example, the present invention may be applied to
multiple coil chambers for launching helicon waves of the type
described in copending application Ser. No. 08/559,345 referenced
above.
[0051] The coil 104 of the illustrated embodiment is made of 1/2 by
1/8 inch heavy duty bead blasted titanium or copper ribbon formed
into a three turn helical coil. However, other highly conductive
materials and shapes may be utilized. For example, the thickness of
the coil may be reduced to {fraction (1/16)} inch and the width
increased to 2 inches. Also, hollow copper tubing may be utilized,
particularly if water cooling is desired. The appropriate RF
generators and matching circuits are components well known to those
skilled in the art. For example, an RF generator such as the ENI
Genesis series which has the capability to "frequency hunt" for the
best frequency match with the matching circuit and antenna is
suitable. The frequency of the generator for generating the RF
power to the coil is preferably 2 MHz but it is anticipated that
the range can vary at other a.c. frequencies such as, for example,
1 MHz to 100 MHz and non-RF frequencies.
[0052] In the illustrated embodiment, the shield 106 has an inside
diameter of 16" but it is anticipated that good results can be
obtained with a width in the range of 6"-25". The shields may be
fabricated from a variety of materials including insulative
materials such as ceramics or quartz. However, the shield and all
metal surfaces likely to be coated with the target material are
preferably made of a material such as stainless steel or copper
unless made of the same material as the sputtered target material.
The material of the structure which will be coated should have a
coefficient of thermal expansion which closely matches that of the
material being sputtered to reduce flaking of sputtered material
from the shield or other structure onto the wafer. In addition, the
material to be cooled should exhibit good adhesion to the sputtered
material. Thus, for example if the deposited material is titanium,
the preferred metal of the shields, coils, brackets and other
structures likely to be coated is bead blasted titanium. Of course,
if the material to be deposited is a material other than titanium,
the preferred metal is the deposited material, stainless steel or
copper. Adherence can also be improved by coating the structures
with molybdenum prior to sputtering the target.
[0053] The wafer to target space is preferably about 140 mm but can
range from about 1.5" to 8". A variety of precursor gases may be
utilized to generate the plasma including Ar, H.sub.2, O.sub.2 or
reactive gases such as NF.sub.3, CF.sub.4 and many others. Various
precursor gas pressures are suitable including pressures of 0.1-50
mTorr. For ionized PVD, a pressure between 10 and 100 mTorr is
preferred for best ionization of sputtered material.
[0054] FIG. 6 is a schematic representation of the electrical
connections of the plasma generating apparatus of the illustrated
embodiment. To attract the ions generated by the plasma, the target
110 is preferably negatively biased by a variable DC power source
400 at a DC power of 3 kW. In the same manner, the pedestal 114 may
be negatively biased by a source 401 at -30 v DC to negatively
biased the substrate 112 to attract the ionized deposition material
to the substrate. One end of the coil 104 is coupled to an RF
source such as the output of an amplifier and matching network 402,
the input of which is coupled to an RF generator 404 which provides
RF power at approximately 4.5 kW. The other end of the coil 104 is
coupled to ground, preferably through a capacitor 406 which may be
a variable capacitor.
[0055] As set forth in greater detail in copending application Ser.
No. 08/680,335, entitled Sputtering Coil for Generating a Plasma,
filed Jul. 10, 1996 (Attorney Docket 1390-CIP/PVD/DV) and assigned
to the assignee of the present application, which application is
incorporated herein in its entirety by reference, the coil 104 may
also be positioned in such a manner that the coil may sputter as
well as the target. As a result, the deposited material may be
contributed by both the target and the coil. Such an arrangement
has been found to improve the uniformity of the deposited layer. In
addition, the coil may have as few turns as a single turn to reduce
complexity and costs and facilitate cleaning.
[0056] FIG. 7 is a cross-sectional view of a support standoff 500
in accordance with an alternative embodiment. In the embodiment of
FIG. 7, the standoff 500 includes a cylindrical insulative base
member 502 and a cup-shaped metal cover member 504 having a
cylindrically shaped side wall 506 spaced from the lateral side 508
of the base member 502 to form a labyrinthine passageway 510
oriented substantially transverse to the wall 140 of the shield.
The base member 502 of the standoff 500 does not have the
concentric channels 300 that the base member 250 of the standoff of
FIG. 4 has. It is believed that for many applications, the passage
way 510 of the standoff 500 of FIG. 7 may suffice in preventing the
formation of a path of deposition material across the standoff
which could short the coil 104 to the shield 106. Because of this
simplification, the base member 502 may be more easily and less
expensively manufactured than the base member 250, particularly
when fabricated from materials such as ceramics which are not
readily machined.
[0057] In accordance with another aspect of the present invention,
the standoff 500 of FIG. 7 comprises a second cup-shaped metal
cover member 512 having a cylindrically shaped side wall 514 spaced
from the side 506 of the first cover member 502 to form a second
labyrinthine passageway 516 oriented generally parallel to the
passageway 510 to further reduce the likelihood of the formation of
a shorting conductive path. However, the second cover member 512
performs another function. The second cover member 512 has a back
wall 518 positioned between a shoulder 520 of the base member 502
and the shield wall 140. The base member shoulder 520 ensures that
the second cover member 512 is tightly engaged against and in good
electrical contact with the shield wall 104 which is maintained at
electrical ground. Accordingly, the second cover member 512, spaced
from the first cover member 504, is likewise maintained at ground.
On the other hand, the first cover member 504 is tightly engaged
against the coil 104. Consequently, the cover member 504 is at the
same potential as the coil 104 and hence may sputter. Because the
second cover member 512 is at ground potential and is positioned to
cover most of the exposed surfaces of the first cover member 504,
it is believed that the second cover member can substantially
reduce sputtering of the first cover member 504 in those
applications in which sputtering of the standoffs is undesirable.
Even in those applications in which the coil 104 is sputtered to
enhance the uniformity of deposition on the substrate, sputtering
of the standoffs may introduce nonuniformities since the standoffs
are typically not arrayed in a continuous ring around the
substrate. Hence, retarding sputtering of the standoffs may be
useful in a number of applications.
[0058] The first insulative base member 502 has a collar 528 which
extends through an opening in the shield wall 140. The standoff 500
further includes a second insulative base member 530 positioned on
the other side of the shield wall 140 from the first insulative
base member 502. Seated in a metal sleeve 531 is a bolt 532 which
passes through interior openings in the sleeve 531, second
insulative base member 530, shield wall 140, second cover member
512, and first insulative base member 502. A nut 534 having flanges
536 passes through openings in the coil 104, first cover member 504
and the first insulative base member 502 and threadably fastens to
the bolt 532. The nut flanges 536 engage the coil 104 and compress
the assembly of the standoff 500 together to secure the standoff
and coil 104 to the shield wall 140.
[0059] The collar 528 of the first insulative base member 502
insulates the metal sleeve 531 and the bolt 532 from the grounded
shield wall 140. A space 538 is provided between the collar 528 and
the second insulative base member 530 so that the compressive force
of the bolt 532 and the nut 534 does not damage the insulative
members which may be made of breakable materials such as ceramics.
The end of the bolt 532 may be covered by a third insulative member
540 which, in the illustrated embodiment is button-shaped. The
second insulative base member has a flange 542 spaced from the
shield wall 140 which receives a lip 544 of the insulative cover
member 540 to retain the cover member 540 in place.
[0060] FIG. 8 is a cross-sectional view of a feedthrough standoff
600 in accordance with an alternative embodiment. Like the support
standoff 500 of FIG. 7, the feedthrough standoff 600 includes a
cylindrical insulative base member 602 and a cup-shaped metal cover
member 604 having a cylindrically shaped side wall 606 spaced from
the lateral side 608 of the base member 602 to form a labyrinthine
passageway 610 oriented substantially transverse to the wall 140 of
the shield. In addition, the standoff 600 of FIG. 8 has a second
cup-shaped metal cover member 612 having a cylindrically shaped
side wall 614 spaced from the side 606 of the first cover member
602 to form a second labyrinthine passageway 616 oriented generally
parallel to the passageway 610 to further reduce the likelihood of
the formation of a shorting conductive path.
[0061] The second cover member 612 is fastened to the shield wall
140 by screw fasteners 617 which ensure that the second cover
member 612 is tightly engaged against and in good electrical
contact with the shield wall 104 and therefore grounded to retard
sputtering of the first cover member 604. An annular shaped channel
618 in the second cover member is coupled to the threaded holes for
the fasteners 617 to vent gases that might inadvertently be trapped
in the fastener holes. A base member shoulder 620 between the end
of the first cover member 604 and the second cover member 612 has
sufficient clearance so as to avoid stress on the insulative base
member 602.
[0062] The first insulative base member 602 has a collar 628 which
extends through an opening in the shield wall 140. Seated in the
insulative base member 602 and the collar 628 is a conductive metal
sleeve 630 which passes from one side of the shield wall 140 to the
other. The standoff 600 further includes a second insulative base
member 632 positioned on the other side of the shield wall 140 from
the first insulative base member 602. Seated in the second
insulative base member 632 and engaging the end of the sleeve 630
is a conductive metal bar 633. Seated in the conductive metal bar
633 is a bolt 634 which passes through interior openings in the bar
633 and sleeve 630 to the coil side of the shield wall 140. A nut
635 having flanges 636 passes through openings in the coil 104,
first cover member 604 and the sleeve 630 and threadably fastens to
the bolt 634. The nut flanges 636 engage the coil 104 and compress
the assembly of the standoff 600 together to secure the feedthrough
standoff and coil 104 to the shield wall 140.
[0063] The collar 628 of the first insulative base member 602
insulates the metal sleeve 630 and the bolt 634 from the grounded
shield wall 140. The second insulative member 632 insulates the
conductive bar 633 from the grounded shield wall 140. RF current
travels along the surface of the conductive bar 633 from an RF
source exterior to the chamber, along the surfaces of the sleeve
630, the first cover member 604 engaging the end of the sleeve to
the coil 104 engaging the first cover member 604. The sleeve 630
has a shoulder 637 to retain the first insulative member 602 in
place. However, a space 638 is provided between the shoulder 637
and the first iinsulative base member 604 so that the compressive
force of the bolt 634 and the nut 635 does not damage the
insulative members which may be made of breakable materials such as
ceramics.
[0064] As set forth above, the conductive bar 633 carrying RF
currents from the exterior generator to the feedthrough is seated
in a second insulative member 632. Covering the other side of the
conductive bar 633 and the end of the bolt 634 is a third
insulative member 640. The insulative members 632 and 640 conform
around the RF conductive members to fill the available space to
avoid leaving spaces larger than a darkspace to inhibit formation
of a plasma and arcing from the conductive bar 633 and the bolt
634.
[0065] In those applications in which sputtering of the coil is
desired to improve deposition uniformity on the substrate, the coil
may be positioned closer to the substrate such that the coil 104 is
within line of sight of the target 110. However, such a position
will likely increase deposition onto the standoffs. In addition, it
is preferred that the coil position not pass the line between the
edge of the target 110 and the edge of the substrate 112 so that
the coil does not "shadow" the substrate 112.
[0066] It will, of course, be understood that modifications of the
present invention, in its various aspects, will be apparent to
those skilled in the art, some being apparent only after study
others being matters of routine mechanical and electronic design.
Other embodiments are also possible, their specific designs
depending upon the particular application. As such, the scope of
the invention should not be limited by the particular embodiments
herein described but should be defined only by the appended claims
and equivalents thereof.
* * * * *