U.S. patent application number 12/125335 was filed with the patent office on 2008-12-04 for apparatus and methods for improving treatment uniformity in a plasma process.
This patent application is currently assigned to NORDSON CORPORATION. Invention is credited to James D. Getty, Jiangang Zhao.
Application Number | 20080296261 12/125335 |
Document ID | / |
Family ID | 40086939 |
Filed Date | 2008-12-04 |
United States Patent
Application |
20080296261 |
Kind Code |
A1 |
Zhao; Jiangang ; et
al. |
December 4, 2008 |
APPARATUS AND METHODS FOR IMPROVING TREATMENT UNIFORMITY IN A
PLASMA PROCESS
Abstract
Apparatus and methods for improving treatment uniformity in a
plasma process. The sacrificial body, which is extends about an
outer peripheral edge of the workpiece during plasma processing, is
composed of a plasma-removable material. The sacrificial body may
include multiple sections that are arranged to define a circular
geometrical shape. The sacrificial body functions to increase the
effective outer diameter of the workpiece, which operates to
alleviate detrimental edge effects intrinsic to plasma processing
by effectively reducing the etch rate near the outer peripheral
edge of the workpiece.
Inventors: |
Zhao; Jiangang; (Concord,
CA) ; Getty; James D.; (Vacaville, CA) |
Correspondence
Address: |
WOOD, HERRON & EVANS, LLP (NORDSON)
2700 CAREW TOWER, 441 VINE STREET
CINCINNATI
OH
45202
US
|
Assignee: |
NORDSON CORPORATION
Westlake
OH
|
Family ID: |
40086939 |
Appl. No.: |
12/125335 |
Filed: |
May 22, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60941518 |
Jun 1, 2007 |
|
|
|
Current U.S.
Class: |
216/67 ;
156/345.51 |
Current CPC
Class: |
H01J 37/32623 20130101;
H01J 2237/3343 20130101; H01J 37/32642 20130101; H01L 21/67069
20130101 |
Class at
Publication: |
216/67 ;
156/345.51 |
International
Class: |
C23F 1/00 20060101
C23F001/00; C23F 1/08 20060101 C23F001/08 |
Claims
1. An apparatus for use in plasma processing a workpiece having an
outer peripheral edge, the apparatus comprising: a sacrificial body
composed of a plasma-removable material, said sacrificial body
adapted to be arranged about the outer peripheral edge of the
workpiece so that an outer diameter of the workpiece is effectively
increased.
2. The apparatus of claim 1 wherein said sacrificial body includes
a plurality of sections arranged to have an annular geometrical
shape when placed in a juxtaposed relationship, said plurality of
sections configured to be arranged concentrically with the
workpiece.
3. The apparatus of claim 1 wherein said sacrificial body is
composed of an organic polymer.
4. The apparatus of claim 3 wherein said organic polymer is
polyetheretherketone (PEEK), polyimide, or polyamide.
5. The apparatus of claim 1 wherein said sacrificial body is
composed of a material similar in composition to a material
constituting a portion of the workpiece exposed to the plasma.
6. The apparatus of claim 1 wherein said sacrificial body has an
annular geometrical shape and an inner diameter approximately equal
to an outer diameter of the outer peripheral edge of the
workpiece.
7. An apparatus for plasma processing a workpiece having an outer
peripheral edge, a first surface, and a second surface connected by
the outer peripheral edge, the apparatus comprising: a vacuum
enclosure configured to contain a plasma, said vacuum enclosure
including a support pedestal adapted to contact and support the
second surface of the workpiece when the first surface of the
workpiece is exposed to the plasma; and a sacrificial body composed
of a plasma-removable material, said sacrificial body extending
about the outer peripheral edge of the workpiece supported on said
pedestal so that an outer diameter of the workpiece is effectively
increased.
8. The apparatus of claim 7 wherein said sacrificial body includes
a plurality of sections arranged to have an annular geometrical
shape when placed in a juxtaposed relationship, said plurality of
sections configured to be arranged concentrically with the
workpiece.
9. The apparatus of claim 8 further comprising: a wafer lift
mechanism disposed inside said vacuum enclosure, said wafer lift
mechanism including a wafer fixture movable between a first
position in which said wafer fixture holds the workpiece in a
non-contacting relationship with said support pedestal and a second
position in which said wafer fixture places the second surface of
the workpiece in a contacting relationship with said support
pedestal, and said first section of said sacrificial body is
carried by said wafer fixture.
10. The apparatus of claim 9 wherein said second section is mounted
adjacent to said support pedestal, and said second section is
stationary when said wafer fixture is moved between the first and
second positions.
11. The apparatus of claim 7 wherein said sacrificial body is
composed of an organic polymer.
12. The apparatus of claim 11 wherein said organic polymer is
polyetheretherketone (PEEK), polyimide, or polyamide.
13. The apparatus of claim 7 wherein said sacrificial body is
composed of a material similar in composition to a material
constituting a portion of the workpiece exposed to the plasma.
14. The apparatus of claim 7 wherein said sacrificial body has an
annular geometrical shape and an inner diameter approximately equal
to an outer diameter of the outer peripheral edge of the
workpiece.
15. A method for plasma etching a workpiece having a first surface,
a second surface, and an outer peripheral edge connecting the first
and second surfaces, the method comprising: arranging a sacrificial
body composed of a plasma-removable material about the outer
peripheral edge of the workpiece; exposing the first surface of the
workpiece and the sacrificial body to a plasma; and shifting a
maximum etch rate from a location on the first surface of the
workpiece to a different location on the sacrificial body.
16. The method of claim 15 further comprising: supporting the first
surface of the workpiece on a support pedestal positioned inside a
vacuum enclosure confining the plasma during the etching
process.
17. The method of claim 15 wherein the sacrificial body is divided
into a plurality of sections that, when aligned, define an annular
geometrical shape, and further comprising: temporarily supporting
the workpiece on a wafer lift mechanism disposed inside the vacuum
enclosure; moving the wafer lift mechanism to transfer the
workpiece from the wafer lift mechanism to the support pedestal;
and when the workpiece is transferred, aligning at least one of the
sections of the sacrificial body with at least another of the
sections of the sacrificial body to define a substantially
continuous annular geometrical shape.
18. The method of claim 17 further comprising: supporting the
workpiece on the support pedestal while the first surface of the
workpiece is etched.
19. The method of claim 15 further comprising: eroding the material
of the sacrificial body with the exposure to the plasma; and
replacing the sacrificial body with another sacrificial body after
sufficient erosion of the sacrificial body occurs.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/941,518, filed Jun. 1, 2007. The disclosure of
this provisional application is hereby incorporated by reference
herein in its entirety.
TECHNICAL FIELD
[0002] The invention generally relates to apparatus and methods for
processing workpieces with a plasma and, more particularly, to
apparatus and methods for improving plasma treatment uniformity in
a plasma processing system.
BACKGROUND
[0003] Uniform plasma treatment for wafer level applications is a
concern for the semiconductor manufacturing industry. One problem
that plagues conventional etch processes and plasma processing
equipment is non-uniformity in the etch rate across a workpiece,
such as a wafer. Workpiece edge effects represent a common source
of these etch rate non-uniformities. The uniformity of the etch
rate can be determined from the quotient of a difference between
the maximum and minimum lateral etch rate on the treated surface to
the product of two times the average etch rate across the
workpiece. Typically, the maximum etch rate occurs near the
peripheral edge of the workpiece and the minimum etch rate is
observed near the workpiece center.
[0004] Conventional methods have been used in the effort to improve
the uniformity of the etch rate across the surface area of the
workpiece. For example, a magnetron may be employed to generate the
plasma. However, such solutions significantly increase the cost of
the plasma processing equipment.
[0005] A cost-effective solution is desired that addresses
workpiece edge effects that occur in conventional processing
systems and that adversely impact the uniformity of the plasma
treatment across the surface area of the workpiece, as well as
other artifacts of the plasma treatment that have a negative
influence on treatment uniformity.
SUMMARY
[0006] In one embodiment, an apparatus is provided for use in
plasma processing a workpiece. The apparatus includes a sacrificial
ring composed of a plasma-removable material. The sacrificial ring
is adapted to be arranged about an outer peripheral edge of the
workpiece so that an outer diameter of the workpiece is effectively
increased.
[0007] In another embodiment, an apparatus is provided for use in
plasma processing a workpiece. The apparatus includes a vacuum
enclosure configured to contain a plasma. The vacuum enclosure
includes a support pedestal adapted to contact and support a second
surface of the workpiece when processing a first surface of the
workpiece with the plasma. The apparatus further includes a
sacrificial ring composed of a plasma-removable material, the
sacrificial ring extending about the outer peripheral edge of the
workpiece supported on the pedestal so that an outer diameter of
the workpiece is effectively increased.
[0008] In yet another embodiment, a method is provided for plasma
processing a workpiece having a first surface, a second surface,
and an outer peripheral edge connecting the first and second
surfaces. The method includes arranging a sacrificial ring composed
of a plasma-removable material about the outer peripheral edge of
the workpiece and exposing the first surface of the workpiece and
the sacrificial ring to a plasma. The method further includes
shifting a maximum etch rate from a location on the first surface
of the workpiece to a different location on the sacrificial
ring.
BRIEF DESCRIPTION OF THE FIGURES
[0009] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention and, together with a general description of the
invention given above, and the detailed description given below,
serve to explain the principles of the embodiments of the
invention.
[0010] FIG. 1 is a perspective view of a plasma processing system
including a vacuum enclosure and a wafer lift mechanism disposed
inside the vacuum enclosure.
[0011] FIG. 2 is a front view of the plasma processing system of
FIG. 1.
[0012] FIG. 3 is an exploded view of the enclosure and wafer lift
mechanism of the plasma processing system of FIGS. 1 and 2.
[0013] FIG. 3A is another exploded view of the workpiece vertical
lift mechanism of the plasma processing system of FIGS. 1, 2, and
3.
[0014] FIG. 4 is a cross-sectional view taken generally along line
4-4 in FIG. 2 in which the wafer lift mechanism is placed in a
raised position with the lid of the vacuum enclosure opened
relative to the base of the vacuum enclosure.
[0015] FIG. 5 is a cross-sectional view similar to FIG. 4 in which
the lid of the vacuum enclosure is in contact with the base of the
vacuum enclosure and the wafer lift mechanism is thereby placed in
a lowered position.
[0016] FIG. 6 is an enlarged view of a portion of FIG. 4.
[0017] FIG. 7 is an exploded view of a portion of the wafer lift
mechanism of FIGS. 1-6.
[0018] FIG. 8A is a perspective view depicting the wafer lift
mechanism in a raised condition in which only a portion of the
wafer lift mechanism is illustrated for clarity of
illustration.
[0019] FIG. 8B is a perspective view similar to FIG. 8A depicting
the wafer lift mechanism in a raised condition.
DETAILED DESCRIPTION
[0020] With reference to FIGS. 1-4, a plasma processing system 10
generally includes a vacuum vessel or enclosure 12 having a lid 14
and a base 16 upon which the lid 14 rests, a pair of support arms
18, 20 connected to the lid 14, an upper electrode 22, and a lower
electrode 24. The processing system 10 further includes a
separating member or ring 26 positioned between the upper and lower
electrodes 22, 24 and contacting confronting faces about the
perimeter of the upper and lower electrodes 22, 24. The confronting
faces of the electrodes 22, 24 are generally planar and parallel
plates and have approximately identical surface areas.
[0021] The support arms 18, 20 mechanically couple the lid 14 with
a lifting device 28 (not shown) is capable of vertically lifting
and lowering the lid 14 relative to the base 16 between a raised
position (FIG. 1) and a lowered position (FIG. 5). When the lid 14
and base 16 are in a contacting relationship, a processing region
28 is defined as the space bounded vertically between the
inwardly-facing horizontal surfaces of the electrodes 22, 24 and
bounded laterally inside the inwardly-facing vertical surface of
the sidewall defined by the separating ring 26. In the raised
position, the processing region 28 is accessible for inserting
unprocessed workpieces 30 and removing processed workpieces 30. In
the lowered position (FIG. 5), an environment may be established in
the processing region 28 that is suitable for plasma processing
each successive workpiece 30 positioned in the processing region
28. The upper electrode 22 moves along with the lid 14 when the lid
14 is moved by the lifting device between the raised and lowered
positions relative to the base 16.
[0022] A power supply 32 (FIG. 2), which is coupled with the
electrodes 22, 24 by shielded coaxial cables or transmission lines
33, 34, respectively, controls the power level and frequency of
operation of the electrodes 22, 24. The power supply 32 may be an
alternating current power supply operating at an extremely low
frequency, such as 50 Hz and 60 Hz, at a high radio frequency, such
as 40 kHz and 13.56 MHz, at a medium radio frequency, such as 1
kHz, or at a microwave frequency, such as 2.4 GHz. The power supply
32 may also operate at dual frequencies superimposed upon one
another. Alternatively, the power supply 32 may be a direct current
(DC) power supply in which the plasma is non-oscillating. In other
alternative embodiments, power supply 32 may supply a radio
frequency (RF) power component that provides dense plasma and a DC
power component that independently increases ion energy without
effecting the plasma density.
[0023] The power supply 32 may be operated at one or more radio
frequencies and include an impedance matching network (not shown)
that measures reflected power from the load represented by the
electrodes 22, 24 and plasma confined therebetween back to the
power supply 32. The impendence matching network adjusts the
frequency of operation of power supply 32 to minimize the reflected
power. The construction of such matching networks is understood by
a person of ordinary skill in the art. For example, the impedance
matching network may tune the matching network by changing the
capacitance of variable capacitors within the matching network to
match the impedance of the power supply 32 to the impedance of the
load as the load changes. The power and voltage levels and
operating frequency(ies) may vary of course, depending upon the
particular application.
[0024] A vacuum pump 36 continuously pumps byproduct generated by
the plasma process and non-reacted source gas from the processing
region 28, when the plasma processing system 10 is operating,
through a vacuum manifold 38. The vacuum pump 36 is operative to
maintain the total pressure in the processing region 28 at a
sub-atmospheric level low enough to facilitate plasma creation.
Typical pressures suitable for plasma formation range from about
twenty (20) millitorr to greater than about fifty (50) torr. The
pressure within the processing region 28 is controlled in
accordance with a particular desired plasma process and primarily
consists of partial pressure contributions from the source gas,
which may comprise one or more individual gas species, supplied to
the evacuated processing region 28.
[0025] With continued reference to FIGS. 1-4, a sealing member 40
is compressed between the separating ring 26 and the upper
electrode 22. When the lid 14 is lowered into contact with the base
16 as shown in FIG. 5, another sealing member 42 is compressed
between the separating ring 26 and a perimeter of the lower
electrode 24. The sealing members 40, 42 are illustrated as
conventional elastomeric O-rings, although the invention is not so
limited. When the lid 14 is in its lowered position, a conducting
member 43 is captured between the respective perimeters of the lid
14 and base 16, which are metallic. The conducting member 43
supplies a good electrical contact between the lid 14 and base
16.
[0026] A gas inlet plate 44 (FIG. 4) is fastened to an upper
horizontal surface of the upper electrode 22. The gas inlet plate
44 is coupled by a gas port 46 and a delivery line 48 with a source
gas supply 50. A mass flow controller and a flow measurement device
(not shown) may be provided that cooperate to regulate the flow of
each process gas from the source gas supply 50 to the gas port 46.
The gas inlet plate 44 includes distribution passages (not shown)
and the upper electrode 22 includes passages (not shown) coupled
with the distribution passages of the gas inlet plate 44. The
passages in the upper electrode 22 communicate with the processing
region 28 for injecting process gas into the process chamber.
[0027] The plasma processing system 10 includes a
microprocessor-based controller 52 (FIG. 2) that is programmed to
control the operation of, among other components, the power supply
32, the vacuum pump 36, and the source gas supply 50. For example,
the controller regulates the power levels, voltages, currents and
frequencies of the power supply 32 and orchestrates the provision
of source gas from source gas supply 50 and the pumping rate of
vacuum pump 36 to define a suitable pressure in processing region
28 in accordance with the particular plasma process and
application.
[0028] During processing of workpiece 30, the power applied between
the electrodes 22, 24 by power supply 32 produces an
electromagnetic field in the processing region 28, which is defined
between the two electrodes 22, 24 when the lid 14 and base 16 are
contacting and an environment suitable for plasma processing is
present in the processing region. The electromagnetic field excites
the atoms or molecules of source gas present in the processing
region to a plasma state, which is sustained by the application of
power from power supply 32 for the duration of the plasma
treatment.
[0029] Transmission line 34, which is electrically coupled in a
known manner with the lower electrode 24, is routed to the lower
electrode 24. Transmission line 33 is electrically coupled in a
known manner with one or both of the electrodes 22, 24. A forced
flow of a cooling fluid may be routed through the air gaps 56
between the electrodes 22, 24 and enclosure 12 for cooling the
processing system 10 and, in particular, for cooling the electrodes
22, 24. To that end, a fitting 54 (FIG. 2) may be provided in the
lid 14 to define a coolant port for coupling a coolant supply 55
(FIG. 2) with these air gaps 56.
[0030] The electrodes 22, 24 are formed from an
electrically-conductive material, such as aluminum. The separating
ring 26 is formed from a non-conducting dielectric material and is
constructed to be able to withstand the plasma environment inside
the processing region 28 without unduly contaminating the processed
workpiece 30. Generally, this implies that the material forming the
separating ring 26 should be substantially resistant to etching by
the plasma present in the processing region 28. The separating ring
26 defines a vertical sidewall of non-conductive material, in
addition to providing the vacuum seal between the electrodes 22,
24.
[0031] Constituent species from the plasma contact and interact
with exposed material on the workpiece 30 to perform the desired
surface modification. The plasma is configured to perform the
desired surface modification of the workpiece 30 by selecting
parameters such as the chemistry of the source gas, the pressure
inside the processing region 28, and the amount of power and/or
frequency applied to the electrodes 22, 24. The processing system
10 may include an end point recognition system (not shown) that
automatically recognizes when a plasma process (e.g., an etching
process) has reached a predetermined end point or, alternatively,
plasma processes may be timed based upon an empirically-determined
time of a process recipe.
[0032] With reference to FIGS. 3, 3A, 4, 5, and 6 in which like
reference numerals refer to like features in FIGS. 1 and 2, the
plasma processing system 10 further includes a vertical lift
mechanism 58 located inside the vacuum enclosure 12. The vertical
lift mechanism 58 receives each workpiece 30 in a lifted condition
relative to the lower electrode 24. The workpiece fixture 60 is
automatically moveable in conjunction with opening and closing the
lid 14 and without operator intervention between a raised position,
when the lid 14 is opened, as best shown in FIG. 4, and a lowered
position when the lid 14 is in a closed position relative to the
base 16, as best shown in FIG. 5. In other words, the workpiece
fixture 60 moves toward the lowered position as the upper electrode
22 is moved by the lid 14 toward the lower electrode 24 to seal the
processing region 28 and moves toward the raised position as the
upper electrode 22 is moved by the lid 14 away from the lower
electrode 24. When the lid 14 is placed in the lowered position
contacting the base 16 to seal the processing region 28 from the
ambient environment, the vertical lift mechanism 58 automatically
places the workpiece 30 in a treatment position.
[0033] The vertical lift mechanism 58 generally includes a
workpiece fixture 60, a set of resiliently-biased supports 62
mechanically coupling the workpiece fixture 60 with the lower
electrode 24, a set of resiliently-biased push devices 64
projecting from the upper electrode 22 toward the lower electrode
24 and the workpiece fixture 60, a lift plate 66, and a workpiece
ring 68. An outer peripheral edge or perimeter 65 of the workpiece
fixture 60, which is positioned between the upper and lower
electrodes 22, 24, is encircled by the separating ring 26.
[0034] As best shown in FIGS. 3 and 3A, the lift plate 66 and
workpiece ring 68 are joined, for example, by a pin-in-socket type
engagement in which one of the lift plate 66 or workpiece ring 68
carries a set of projecting pins (not shown) and the other of the
lift plate 66 or workpiece ring 68 carries a set of sockets (not
shown) that register and mate with the pins. A cover plate 70,
which is disposed on the lower electrode 24, includes a cap 72 and
a support 74 that underlies the cap 72. The cap 72 may also be
joined with the support 74 by a pin-in-socket type engagement or,
alternatively, the cap 72 and support 74 may constitute an
integral, one-piece component. The cover plate 70 has a good
electrical contact with the lower electrode 24, as does the
workpiece ring 68 and lift plate 66, when the lid 14 is lowered. As
a consequence, the workpiece fixture 60, the workpiece 30, and the
lower electrode 24 are at approximately equivalent electrical
potentials when the plasma processing system 10 is operating to
generate plasma inside the processing region 28 and to process
workpieces 30 inside the processing region 28 with the plasma.
[0035] A recess 76 is located near each of the corners of the lower
electrode 24. Each recess 76 has a base 78 that represents a
relatively thin wall of the material of lower electrode 24
remaining after the respective recess 76 is formed or machined in
the lower electrode 24. Projecting from the base 78 of each of the
recesses 76 is a mounting post 80 with an internally threaded
opening 82. Each mounting post 80 may be positioned to be
substantially coaxial with the respective one of the recesses 76.
In the assembly forming the support 62, a threaded tip 84 of a
guide pin 86 is mated with the internally threaded opening 82 of
each mounting post 80. The internally threaded opening 82 of each
mounting post 80 is oriented such that the respective guide pin 86
projects in a direction toward the lift plate 66.
[0036] Each of the recesses 76 is also bounded peripherally by a
substantially cylindrical sidewall 88 extending to the base 78 and
a beveled or flared rim 90 disposed between sidewall 88 and a top
surface 92 of the lower electrode 24. The diameter of the flared
rim 90, which intersects the top surface 92, is greater than the
diameter of the sidewall 88 of each recess 76 and diverges with
increasing diameter in a direction toward the top surface.
[0037] Each guide pin 86 includes a substantially cylindrical,
non-threaded shank 94 extending from the threaded tip 84 toward a
head 96. The head 96 may include a recessed feature 98 that
receives the tip of a tool (not shown) used to generate the mated
engagement between the threaded tip 84 of guide pin 86 and the
internally-threaded opening 82. The head 96 of each guide pin 86,
which projects at least partially above the nearby top surface 92
of the lower electrode 24, carries a flared surface 100 located
near the non-threaded shank 94. The non-threaded shank 94 of each
guide pin 86 and the sidewall 88 of the respective recess 76 have a
substantially coaxial arrangement.
[0038] Each of the supports 62 includes a stop block 102 coupled by
a respective one of the guide pins 86 with the lift plate 66 of the
workpiece fixture 60. Each stop block 102 includes a body 104 with
an enlarged head 106 and a central bore or passageway 108 extending
the length of the body 104. The radially outward projection of
enlarged head 106 relative to the body 104 defines an edge or lip
110, which extends circumferentially about the body 104. The
enlarged head 106 of each stop block 102 further includes a first
beveled or tapered exterior sidewall 112 that decreases in diameter
with increasing distance from the lip 110 and a second beveled or
tapered exterior sidewall 114 that increases in diameter with
increasing distance from the lip 110. The exterior sidewall 114 is
disposed between the lip 110 and the tapered exterior sidewall 112.
The passageway 108 includes a substantially cylindrical surface 116
and a beveled or tapered surface 118 that narrows a portion of the
substantially cylindrical surface 116.
[0039] A flared recess 120 is defined near each of the peripheral
corners of the lift plate 66. The tapered exterior sidewall 112 of
each stop block 102 is engaged with a respective one of the flared
recesses 120. The depth of each flared recess 120 is selected such
that a respective inclined surface 122 of the flared recess 120 and
tapered exterior sidewall 112 of each stop block 102 are contacting
when the lift plate 66 is secured with the stop blocks 102. The
inclination angles of each flared recess 120 and the corresponding
tapered exterior sidewall 112 of its stop block 102 are matched to
assist in securing the stop blocks 102 with the lift plate 66, yet
permit ready removability of the lift plate 66 by a vertical force
of sufficient magnitude.
[0040] When mounted to the lift plate 66, the tapered surface 118
of passageway 108 in stop block 102 is located generally between
one of the recesses 76 in the lower electrode 24 and the workpiece
fixture 60. Disposed in each of the recesses 76 is a spring element
124, which may have the form of a compression spring formed from a
helical coil of wire. Each spring element 124 is confined within
the respective recess 76 and is captured between the base 78 and
the lip 110 on the respective stop block 102.
[0041] As best shown in FIG. 6, the spring elements 124 are
extended when the workpiece fixture 60 is in the raised position.
As a result, the lift plate 66 and workpiece ring 68 of the
workpiece fixture 60 are supported in a resiliently floating manner
atop the supports 62. Under the load supplied by the lift plate 66
and workpiece ring 68, the spring elements 124 collectively have a
spring force sufficient to suspend or elevate the lift plate 66
above the top surface 92 of lower electrode 24.
[0042] The tapered surface 118 contacts the flared surface 100 on
the head 96 of guide pin 86 to provide a positive stop for vertical
motion when the workpiece fixture 60 is in the raised position. The
inclination angles of the flared surface 100 and the tapered
surface 118 are matched so that each stop block 102 is
self-centered on the respective guide pin 86 when the workpiece
fixture 60 is in the raised position. This permits the workpiece
fixture 60 to return to a reproducible spatial location when
residing in the raised position. In turn, this provides a
reproducible location within plasma processing system 10 for the
workpiece 30 carried by the workpiece fixture 60.
[0043] As explained in detail below, movement of the lid 14 toward
a lowered position (FIG. 5) moves the workpiece fixture 60 toward a
lowered position and, thereby, compresses the spring elements 124.
As the workpiece fixture 60 is lowered, the head 96 of each of the
guide pins 86 moves in its respective passageway 108 toward the
lift plate 66.
[0044] As best shown in FIGS. 3 and 3A, the workpiece fixture 60
includes a central opening 130 extending entirely through the lift
plate 66 and workpiece ring 68, and a gap 132 that extends radially
from the central opening 130 to the outer perimeter 65 of the
workpiece fixture 60. The cover plate 70 is dimensioned with a
width substantially identical to the width of the gap 132. When the
workpiece fixture 60 is lowered to a process position, the cover
plate 70 fills the gap 132 so that the central opening 130 is
surrounded by a substantially planar surface defined collectively
by a top surface 134 of the workpiece ring 68 and a top surface 136
of the cover plate 70. To promote the requisite coplanar
arrangement, the respective thicknesses of the cover plate 70 and
workpiece fixture 60 are selected to be approximately equal, which
permits the top surfaces 134, 136 to be approximately flush when
the workpiece fixture 60 is in its lowered position. The central
opening 130 is round in the representative embodiment. However, the
central opening 130 may have other shapes, such as rectangular.
[0045] The gap 132 is defined between confronting sidewalls 133,
135 extending through the thickness of the workpiece ring 68. The
width of the gap 132 in the workpiece fixture 60 is selected such
that an end effector can pass through the gap 132 and access the
central opening 130 for transferring unprocessed workpieces 30 to
the workpiece fixture 60 and removing processed workpieces 30 from
the workpiece fixture 60. The end effector is operatively coupled
with a robot, such as a selective compliant articulated/assembly
robot arm (SCARA) robot, as understood by a person having ordinary
skill in the art.
[0046] The lower electrode 24 further comprises a removable
electrode section 138, which includes a mounting flange 140
situated in a recess defined in the lower electrode 24 and a
pedestal portion 142. The pedestal portion 142, which defines a
representative workpiece support, projects from the mounting flange
140 toward the upper electrode 22. The electrode section 138 is
secured with conventional fasteners to the underlying and
surrounding remainder of the lower electrode 24. The top surface 92
of lower electrode 24 and the top surface 92 of the mounting flange
140 are approximately flush. The surface area of a top surface 144
of the pedestal portion 142, which is elevated above the
surrounding mounting flange 140, is approximately equal to the open
cross-sectional area radially inside the central opening 130. The
diameter of the pedestal portion 142 is approximately equal to the
diameter of the central opening 130 of workpiece ring 68. The
electrode section 138 has a good electrical contact with the
remainder of the lower electrode 24 so that the pedestal portion
142 and support 74 are at substantially the same potential as the
lower electrode 24 when the plasma processing system 10 is
operating and a plasma is present in the processing region 28.
[0047] The cover plate 70 comprises another raised region of the
electrode section 138 that projects above the plane of the mounting
flange 140. The cover plate 70 and pedestal portion 142 may
comprise a single or unitary raised region projecting from the
mounting flange 140. Alternatively, the cover plate 70 may comprise
a separate component that is mounted to the electrode section 138
and, in this instance, may include locating pins (not shown) or the
like used to automatically position the cover plate 70 relative to
the central opening 130 in the workpiece fixture 60.
[0048] When the workpiece fixture 60 is lowered to a process
position, contact between the workpiece 30 and the top surface 144
of pedestal portion 142 transfers the workpiece 30 from the
workpiece ring 68 to the pedestal portion 142. The transfer of the
workpiece 30 is accomplished without any structure on the pedestal
portion 142, the lower electrode 24, or the base 16 of the
enclosure 12 guiding the workpiece 30 onto the pedestal portion
142. In the lowered process position of the workpiece fixture 60,
the top surface 134 of workpiece ring 68 is recessed slightly below
the top surface 144 of the pedestal portion 142. During plasma
treatment, the workpiece 30 rests on the top surface 144 of the
pedestal portion 142.
[0049] The electrode section 138 and the lift plate 66 are
constructed from an electrical conductor, such as aluminum. The cap
72 on the cover plate 70 and the workpiece ring 68 are constructed
from an electrical insulator or dielectric, such as alumina or
high-purity alumina. Alternatively, the cap 72 on the cover plate
70 and the workpiece ring 68 may also be constructed from an
electrical conductor, such as aluminum. The selection of a
constituent material for the cap 72 of the cover plate 70 and the
workpiece ring 68 is dictated by the type of plasma performance
required in the plasma processing system 10 for a particular plasma
process on workpiece 30.
[0050] With reference to FIGS. 3A and 4, one of the push devices 64
is located spatially near each inside corner 15 of separating ring
26 and, as apparent, near each corresponding outside corner (not
shown) of the upper electrode 22. Each of the push devices 64
includes a pusher block 150, which is secured with the upper
electrode 22 by the cooperation between an insert 152 and a
shoulder bolt 154, and a spring element 156. Each of the pusher
blocks 150 has a substantially overlying relationship with a
respective one of the stop blocks 102. One end of the spring
element 156, which may have the form of a compression spring formed
from a helical coil of wire, is captured between an enlarged head
158 of the pusher block 150 and the upper electrode 22. The pusher
block 150 is constructed from an insulating or dielectric material,
such as a ceramic, and the insert 152 and shoulder bolt 154 may be
formed from a metal, such as a stainless steel. The shoulder bolt
154 has a threaded tip that is fastened in a threaded bolt hole in
the upper electrode 22. The pusher block 150 of each push device 64
is movable relative to the shoulder bolt 154 between a first
position (FIG. 4) in which the spring element 156 is extended and a
second position (FIG. 5) in which the spring element 156 is
compressed. The spring element 156 supplies a preloaded bias to
each pusher block 150 in the first position.
[0051] As the lid 14 is moved toward the base 16, the pusher block
150 of each of the push devices 64 contacts the top surface 134 of
workpiece ring 68 and the spring elements 156 begin to compress. As
the lid 14 approaches the base 16, the spring elements 156 are
further compressed, which applies an increasing force to the
workpiece ring 68 that causes the workpiece fixture 60 to move
toward the top surface 144 of the pedestal portion 142 and toward
the lower electrode 24. When the workpiece fixture 60 is in the
fully lowered position, the tapered exterior sidewall 114 on each
stop block 102 contacts the flared rim 90 of recess 76 and each
pusher block 150 is moved to its second position.
[0052] The inclination angles of the flared rim 90 and tapered
exterior sidewall 114 are approximately equal or matched. When the
workpiece fixture 60 is in the lowered position, each of the flared
rims 90 is in contact with the respective one of the exterior
sidewalls 114. The contact automatically self-centers each stop
block 102 within its respective recess 76. Consequently, each time
that the lid 14 is lowered, the workpiece fixture 60 returns to a
reproducible spatial location relative to the lower electrode 24
and removable electrode section 138 when the lid 14 moves the
workpiece fixture 60 to the lowered position. In turn, this
provides a reproducible location for successive workpieces 30 on
the pedestal portion 142 during each sequential plasma
treatments.
[0053] With reference to FIGS. 3, 3A, 7, 8A, and 8B in which like
reference numerals refer to like features and in accordance with an
embodiment of the invention, the plasma processing system 10
further includes a sacrificial ring, which is generally indicated
by reference numeral 160. When the bottom surface 29 of workpiece
30 is supported on the top surface 144 of the pedestal portion 142,
the sacrificial ring 160 extends circumferentially about an outer
peripheral edge 31 encircling the perimeter of the workpiece 30 in
a concentric relationship with the workpiece 30.
[0054] The sacrificial ring 160 includes a body 161 consisting of a
first section 168 that is mounted to a curved shoulder 164 of the
lift plate 66 of workpiece ring 68 and a second section 170 that is
mounted to a shoulder 166 of the support 74 of cover plate 70. The
first section 168 comprises an arc of greater arc length than the
arc presented by the second section 170. The curved shoulder 164,
which is defined in the lift plate 66 of the workpiece ring 68,
coaxially encircles the central opening 130 and terminates at an
intersection with sidewalls 133, 135 that flank the gap 132. The
curved shoulder 164, which opens onto the central opening 130, is
recessed relative to the top surface 92 of the workpiece ring 68.
The curved shoulder 166, which is defined in the support 74 of the
cover plate 70, is juxtaposed with the shoulder 164 when workpiece
fixture 60 is in the lowered position to geometrically close a
complete circular object. Shoulder 166, which also opens onto the
central opening 130, is recessed relative to the top surface 136 of
the cover plate 70. The sections 168, 170 of the sacrificial ring
160 may be secured with the lift plate 66 and support 74 by a
pin-in-socket type engagement using pins 172, 174,
respectively.
[0055] The first section 168 of the sacrificial ring 160 includes a
ridge 176 and a shoulder or rim 178 that is disposed radially
inside of the ridge 176. The ridge 176 of the first section 168
projects above the rim 178 so that the peripheral edge 31 of
workpiece 30, which connects the top and bottom surfaces 27, 29 of
workpiece 30, overlies the rim 178 and is disposed radially inside
of ridge 176. Likewise, the second section 170 of the sacrificial
ring 160 includes a ridge 180 and a shoulder or rim 182 that is
disposed radially inside of the ridge 180. The ridge 180 of the
second section 170 projects above the rim 182 so that the
peripheral edge 31 of workpiece 30 overlies the rim 182 and is
disposed radially inside of rim 182. The sections 168, 170 may each
be formed from multiple segments of material (i.e., a narrow
segment having an inner edge with a larger radius of curvature on a
wide segment with an inner edge of smaller radius of curvature) or,
alternatively, may be machined or molded from a single, integral
piece of material.
[0056] The radial dimension or width of the rim 178 is selected
such that only a thin annular surface area on the bottom surface 29
and extending about the peripheral edge 31 of the workpiece 30 is
contacted by the rim 178. In one embodiment, the contacted width
may be an annulus extending approximately equal to 3 millimeters
radially inward from the peripheral edge 31 of workpiece 30. The
diameter of the central opening 130 in the lift plate 66 is
approximately equal to the diameter of the workpiece 30 less the
radial dimension of the rims 178, 182.
[0057] As best shown in FIG. 8B, the ridges 176, 180 are aligned
with each other, as are the rims 178, 182, in a substantially
continuous, annular geometrical shape when the workpiece fixture 60
is in the lowered process position. The relationship between the
sections 168, 170 is shown in FIG. 8A with the workpiece fixture 60
is its elevated condition and in FIG. 8B with the workpiece fixture
60 in its lowered condition with the lid 14 closed and ready to
process the workpiece 30. The alignment of the ridges 176, 180,
when the workpiece fixture 60 is lowered, defines a substantially
continuous ring of material with a radial dimension that
effectively shifts the location of the outer peripheral edge of the
workpiece 30 radially outward toward the outer diameter of the
sacrificial ring 160. The top surface of the ridges 176, 180 are
substantially co-planar with the adjacent top surface of the
workpiece 30. The sacrificial ring 160 has a non-contacting
relationship with the workpiece 30 when the workpiece fixture 60 is
in its lowered position.
[0058] The sacrificial ring 160, which in one embodiment may be
about 10 millimeters wide, is formed from a consumable material
that etches when exposed to the plasma. The consumable material may
be composed of an organic polymer or another material (i.e.,
silicon) similar in composition to the material of the workpiece 30
to be plasma etched. Suitable organic polymers may include, but are
not limited to, polyetheretherketone (PEEK), polyimide, and
polyamide or nylon. The sacrificial ring 160 may be fabricated from
these types of materials by techniques familiar to a person having
ordinary skill in the art.
[0059] Organic polymers may be particular suitable materials for
the composition of the sacrificial ring 160 if, for example, the
plasma of the plasma treatment system 10 is being used to strip a
layer of photoresist from the workpiece 30. In this instance, the
material composing the sacrificial ring 160 is similar to the
composition of the material being removed by plasma etching from
the workpiece. When eroded by plasma etching, the material of the
sacrificial ring 160 may form etch byproducts that are relatively
volatile and, as a result, that are readily evacuated from the
processing region 28 by vacuum pump 36. Accordingly, the
contamination or residue on the sidewalls 13 of vacuum enclosure 12
and the components therein, including the workpiece 30 itself, from
the etching of the sacrificial ring 160 may be negligible.
[0060] The radial dimension of the ridges 176, 180 is selected to
optimize the shift in the effective location of the peripheral edge
of the workpiece 30. In other words, the workpiece 30 presents a
larger effective diameter to the plasma so that the intrinsic zone
of relatively high etch rate, which originates from workpiece edge
effects, etches the sacrificial ring 160, rather than the workpiece
30 at its peripheral rim. The uniformity of plasma treatment across
the workpiece 30 is improved because this higher etch rate is
shifted radially outwardly and off the workpiece 30. The ridges
176, 180 are exposed to the plasma in the processing region 28 when
the system 10 is used to generate plasma and treat the top surface
27 of the workpiece 30. Generally, the sacrificial ring 160 has an
annular geometrical shape characterized by an inner diameter, ID,
approximately equal to an outer diameter of the outer peripheral
edge 31 of the workpiece 30. The difference in the inner diameter,
ID, and the outer diameter of the sacrificial ring 160 defines its
effective radial dimension.
[0061] The sacrificial ring 160 can be used to shift the edge
effect inherent in plasma treatment from the outer peripheral edge
31 of the workpiece 30 to a perimeter 162 of the sacrificial ring
160. By this mechanism and although not wishing to be limited by
theory, the sacrificial ring 160 is believed to operate to
alleviate or mitigate the workpiece edge effect at the periphery by
sacrificing its own treatment uniformity during plasma processes as
the preferential edge effect increases the etch rate mainly over
the consumable material of the sacrificial ring 160. Consequently,
the etch rate is more uniform across the workpiece 30 as less
variation in etch rate occurs between central and peripheral edge
regions of workpiece 30.
[0062] The lifetime of the sacrificial ring 160 for maintaining its
effectiveness in effectively shifting the location of the outer
peripheral edge of the workpiece 30 may be contingent upon its
constituent material and the specifics of the plasma process. The
sacrificial ring 160 may be replaced, as necessary, as it is a
consumable component.
[0063] The sacrificial ring 160 represents a simple and effective
technique for improving the across-wafer uniformity of a plasma
treatment in a wafer level application, such as plasma etching,
photoresist stripping or descumming, surface cleaning, surface
activation, and thin film deposition. The sacrificial ring 160 can
be implemented without significantly increasing the capital cost of
the plasma treatment system 10. Furthermore, the sacrificial ring
160 can be used to improve the uniformity of plasma treatment
across the workpiece without requiring time-consuming or expensive
etch processes or etch equipment. Plasma treatment systems can be
retrofit, in a simple and inexpensive manner, with the sacrificial
ring 160 to address the etch uniformity problems arising from edge
effects.
[0064] References herein to terms such as "vertical", "horizontal",
etc. are made by way of example, and not by way of limitation, to
establish a three-dimensional frame of reference. The term
"horizontal" as used herein is defined as a plane substantially
parallel to a plane containing one of the confronting surfaces of
the electrodes 22, 24, regardless of orientation. The term
"vertical" refers to a direction perpendicular to the horizontal,
as just defined. Terms, such as "upper", "lower", "on", "above",
"below", "side" (as in "sidewall"), "higher", "lower", "over",
"beneath" and "under", are defined with respect to the horizontal
plane. It is understood various other frames of reference may be
employed without departing from the spirit and scope of the
invention as a person of ordinary skill will appreciate that the
defined frame of reference is relative as opposed to absolute.
[0065] While the invention has been illustrated by a description of
various embodiments and while these embodiments have been described
in considerable detail, it is not the intention of the applicants
to restrict or in any way limit the scope of the appended claims to
such detail. Additional advantages and modifications will readily
appear to those skilled in the art. The invention in its broader
aspects is therefore not limited to the specific details,
representative apparatus and methods, and illustrative examples
shown and described. Accordingly, departures may be made from such
details without departing from the spirit or scope of applicant's
general inventive concept. The scope of the invention itself should
only be defined by the appended claims.
* * * * *