Title: Method and apparatus for the compensation of edge ring wear in a plasma processing chamber
Abstract: A method for processing a plurality of substrates in a plasma processing chamber of a plasma processing system, each of the substrate being disposed on a chuck and surrounded by an edge ring during the processing. The method includes processing a first substrate of the plurality of substrates in accordance to a given process recipe in the plasma processing chamber. The method further includes adjusting, thereafter, a capacitance value of a capacitance along a capacitive path between a plasma sheath in the plasma processing chamber and the chuck through the edge ring by a given value. The method additionally includes processing a second substrate of the plurality of substrates in accordance to the given process recipe in the plasma processing chamber after the adjusting, wherein the adjusting is performed without requiring a change in the edge ring.
Patent Number: 6,896,765 Issued on 05/24/2005 to Steger
| Inventors:
|
Steger; Robert J. (Los Altos, CA)
|
| Assignee:
|
Lam Research Corporation (Fremont, CA)
|
| Appl. No.:
|
247812 |
| Filed:
|
September 18, 2002 |
| Current U.S. Class: |
156/345.51; 118/728 |
| Intern'l Class: |
H01L 021/30.6 |
| Field of Search: |
156/34551
118/728
361/234
250/281
|
References Cited [Referenced By]
U.S. Patent Documents
Primary Examiner: Niebling; John F.
Assistant Examiner: Stevenson; Andre′ C.
Attorney, Agent or Firm: IP Strategy Group PC
Claims
1. A plasma processing system having at least one plasma processing chamber for
processing a plurality of substrates, said plasma processing chamber comprising:
a chuck configured for supporting a substrate during said processing;
an edge ring having an outer periphery, said outer periphery of said edge ring
surrounding said chuck, wherein said edge ring is disposed along a capacitive path
between a plasma sheath and said chuck during said processing, said plasma sheath
being associated with a plasma generated during said processing;
a coupling ring disposed along said capacitive path; and,
an arrangement for adjusting a capacitance value of a capacitance disposed along
said capacitive path, said adjusting comprises moving, along an axis that is substantially
perpendicular to a surface of said edge ring, one of said edge ring and said coupling
ring to adjust a gap between adjacent surfaces, said adjacent surfaces including
a said surface of said edge ring and a surface of said coupling ring.
2. The plasma processing system of claim 1 wherein said arrangement is coupled
to said coupling ring and is configured to move said coupling ring along an axis
that is perpendicular to said surface of said edge ring to increase said gap.
3. The plasma processing system of claim 1 wherein said arrangement includes
an actuator.
4. The plasma processing system of claim 3 wherein said actuator is a linear actuator.
5. The plasma processing system of claim 3 wherein said actuator is a screw actuator.
6. The plasma processing system of claim 1 wherein said capacitance value of
said capacitance disposed along said capacitive path is decreased by a given value,
said given value represents a capacitance value sufficient to offset a first increase
in capacitance along said capacitive path, said first increase in capacitance being
attributable to thinning damage of said edge ring.
7. The plasma processing system of claim 1 wherein said processing includes etching
said substrate.
8. The plasma processing system of claim 1 wherein said processing includes depositing
a layer of material on said substrate.
9. A plasma processing system having at least one plasma processing chamber for
processing a plurality of substrates, said plasma processing chamber comprising:
a chuck configured for supporting a substrate during said processing;
an edge ring having an outer periphery, said outer periphery of said edge ring
surrounding said chuck, wherein said edge ring is disposed alone a capacitive path
between a plasma sheath and said chuck during said processing, said plasma sheath
being associated with a plasma generated during said processing; and,
an arrangement for adjusting a capacitance value of a capacitance disposed alone
said capacitive path, wherein said capacitance represents a variable impedance
device, said arrangement for adjusting said capacitance value of said capacitance
includes an adjustment mechanism for adjusting a capacitance value of said variable
impedance device.
10. A plasma processing system having at least one plasma processing chamber
for processing a plurality of substrates, said plasma processing chamber comprising:
supporting means for supporting a substrate during said processing;
an edge ring having an outer periphery, said outer periphery of said edge ring
surrounding said supporting means, wherein said edge ring is disposed along a capacitive
path between a plasma sheath and said supporting means during said processing,
said plasma sheath being associated with a plasma generated during said processing;
a coupling ring disposed along said capacitive path; and,
means for adjusting a capacitance value of a capacitance disposed along said
capacitive path, said adjusting comprises moving, along an axis that is substantially
perpendicular to a surface of said edge ring, one of said edge ring and said coupling
ring to adjust a gap between adjacent surfaces, said adjacent surfaces including
said surface of said edge ring and a surface of said coupling ring.
11. The plasma processing system of claim 10 wherein said means for adjusting
is coupled to said coupling ring and is configured to move said coupling ring along
an axis that is substantially perpendicular to said surface of said edge ring to
increase said gap.
12. The plasma processing system of claim 10 wherein said means for adjusting
is coupled to said coupling ring and is configured to move said coupling ring along
an axis that is substantially perpendicular to said surface of said edge ring to
decrease said gap.
13. The plasma processing system of claim 10 wherein said means for adjusting
includes one of a linear actuator and a screw actuator.
14. The plasma processing system of claim 10 wherein said capacitance value of
said capacitance disposed along said capacitive path is decreased by a given value,
said given value represents a capacitance value sufficient to offset a first increase
in capacitance along said capacitive path, said first increase in capacitance being
attributable to thinning damage of said edge ring from said processing.
15. The plasma processing system of claim 10 wherein said capacitance value of
said capacitance disposed along said capacitive path is increased by a given value,
said given value represents a capacitance value sufficient to offset a first decrease
in capacitance along said capacitive path, said first decrease in capacitance being
attributable a build up of material on said edge ring from said processing.
Description
BACKGROUND OF THE INVENTION
The present invention relates in general to substrate manufacturing technologies
and in particular to methods and apparatus for improving process results by compensating
for edge ring wear in a plasma processing chamber.
In the processing of a substrate, e.g., a semiconductor wafer or a glass panel
such as one used in flat panel display manufacturing, plasma is often employed.
As part of the processing of a semiconductor wafer, for example, the wafer is
divided into a plurality of dies, or rectangular areas, each of which will become
an integrated circuit. The wafer is processed in a series of steps in which materials
are selectively removed (etching) and deposited (deposition) in order to form electrical
components thereon.
In an exemplary plasma etching process, the wafer is coated with a thin film
of
hardened emulsion (i.e., such as a photoresist mask) prior to etching. Areas of
the hardened emulsion are then selectively removed, causing parts of the underlying
layer to become exposed. The wafer is then placed in a plasma processing chamber
on a negatively charged electrode, called a chuck. Appropriate etchant source gases
are then flowed into the chamber and struck to form a plasma to etch exposed areas
of the underlying layer(s). In an exemplary plasma deposition process, plasma is
also employed to facilitate and/or improve deposition from the source deposition materials.
In many plasma processing chambers, an edge ring is often employed. To facilitate
discussion, FIG. 1 illustrates a simplified cross section view of a plasma processing
chamber
100. A wafer
104 sits on a chuck
112 which supports
the wafer in the plasma processing chamber. Chuck
112 acts as a work piece
holder and may be electrically energized by an RF power source to facilitate etching
and deposition, as is well known. A coupling ring
108 is shown disposed
between chuck
112 and a ceramic ring
110. One of the functions of
coupling ring
108 includes providing a current path from chuck
112
to an edge ring
102. Edge ring
102 performs many functions, including
positioning wafer
104 on chuck
112 and shielding the underlying components
not protected by the wafer itself from being damaged by the ions of the plasma.
One important function of edge ring
112 relates to its effect on process
uniformity across the substrate. It is well known that the equipotential lines
of the plasma sheath
106 curve upward sharply past the edge of the chuck.
Without an edge ring, the substrate edge electrically defines the outer edge of
the chuck, and the equipotential lines would curve upward sharply in the vicinity
of the substrate edge. As such, areas of the substrate around the substrate edge
would experience a different plasma environment from the plasma environment that
exists at the center of substrate, thereby contributing to poor process uniformity
across the substrate surface.
By electrically extending the plasma-facing area of the chuck with an edge ring
and/or other underlying structures, the edge of the chuck appears electrically
to the plasma to extend some distance outside of the edge of the substrate. Thus,
the equipotential lines of the plasma sheath stays more constant over the entire
surface of the substrate, thereby contributing to process uniformity across the
substrate surface.
Unfortunately, edge rings tend to be worn away over time by the plasma
environment. As the edge ring wears away, the plasma environment in the vicinity
of the damaged regions of the edge ring changes. The change to the plasma in turn
causes the process result to change over time, and contributes to process degradation
as the edge ring wears away. This is the case even if the process employs the same
recipe in the same chamber time after time.
Over time, the process result degrades to the point where an edge ring change
is necessary. When an edge ring change is required, substrate processing is brought
to a halt, and the plasma processing chamber is taken out of service in order to
facilitate an edge ring change. During the edge ring change operation, which may
take hours or days, the manufacturer is deprived of the use of the affected plasma
processing system, which contributes to a higher cost of ownership for the plasma
processing system.
In view of the foregoing, there are desired improved methods and apparatus for
improving process results in a plasma processing system that employs edge rings,
as well as for reducing the frequency with which an edge ring change is required.
SUMMARY OF THE INVENTION
The invention relates, in one embodiment, to a method for processing a plurality
of substrates in a plasma processing chamber of a plasma processing system, each
of the substrate being disposed on a chuck and surrounded by an edge ring during
the processing. The method includes processing a first substrate of the plurality
of substrates in accordance to a given process recipe in the plasma processing
chamber. The method further includes adjusting, thereafter, a capacitance value
of a capacitance along a capacitive path between a plasma sheath in the plasma
processing chamber and the chuck through the edge ring by a given value. The method
additionally includes processing a second substrate of the plurality of substrates
in accordance to the given process recipe in the plasma processing chamber after
the adjusting, wherein the adjusting is performed without requiring a change in
the edge ring.
In another embodiment, the invention relates to a plasma processing system having
at least one plasma processing chamber for processing a plurality of substrates.
The plasma processing chamber includes a chuck configured for supporting a substrate
during the processing and an edge ring having an outer periphery. The outer periphery
of the edge ring surrounds the chuck, wherein the edge ring is disposed along a
capacitive path between a plasma sheath and the chuck during the processing, the
plasma sheath being associated with a plasma generated during the processing. The
plasma processing chamber additionally includes an arrangement for adjusting in-situ
a capacitance value of a capacitance disposed along the capacitive path.
In yet another embodiment, the invention relates to a plasma processing system
having at least one plasma processing chamber for processing a plurality of substrates.
The plasma processing chamber includes supporting means for supporting a substrate
during the processing. There is further included an edge ring having an outer periphery,
the outer periphery of the edge ring surrounding the supporting means, wherein
the edge ring is disposed along a capacitive path between a plasma sheath and the
supporting means during the processing, the plasma sheath being associated with
a plasma generated during the processing. Additionally, there is included means
for adjusting in-situ a capacitance value of a capacitance disposed along the capacitive path.
These and other features of the present invention will be described in more
detail below in the detailed description of the invention and in conjunction with
the following figures.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is illustrated by way of example, and not by way of limitation,
in the figures of the accompanying drawings and in which like reference numerals
refer to similar elements and in which:
FIG. 1 depicts a simplified cross section view of a plasma processing chamber;
FIG. 2A depicts a simplified cross section view of a plasma processing chamber
according to an embodiment of the invention;
FIG. 2B depicts a simplified electrical diagram for a capacitive path according
to an embodiment of the invention;
FIG. 3A depicts a simplified cross section view of a plasma processing chamber
according to an embodiment of the invention;
FIG. 3B depicts a simplified electrical diagram for a capacitive path according
to an embodiment of the invention;
FIG. 4A depicts a simplified cross section view of a plasma processing chamber
according to an embodiment of the invention; and,
FIG. 4B depicts a simplified electrical diagram for a capacitive path according
to an embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will now be described in detail with reference to a few
preferred embodiments thereof as illustrated in the accompanying drawings. In the
following description, numerous specific details are set forth in order to provide
a thorough understanding of the present invention. It will be apparent, however,
to one skilled in the art, that the present invention may be practiced without
some or all of these specific details. In other instances, well known process steps
and/or structures have not been described in detail in order to not unnecessarily
obscure the present invention. The features and advantages of the present invention
may be better understood with reference to the drawings and discussions that follow.
While not wishing to be bound by theory, it is believed by the inventor herein
that when the edge ring is worn away, the capacitance along the capacitive path
from the plasma sheath to the chuck through the edge ring changes. The change in
the capacitance in turn affects the plasma environment in the vicinity of the damaged
regions of the edge ring. Unless this change in capacitance is compensated for
as the edge ring wears away, process degradation is inevitable. Furthermore, without
compensating for the change in capacitance as the edge ring wears away, the process
degradation is uncorrected and necessitates more frequent edge ring changes.
To facilitate discussion, FIG. 2A illustrates another plasma processing chamber
diagram is which the capacitive path
150 from plasma sheath
106 to
chuck
112 through edge ring
102 is depicted. Referring now to FIG.
2A, plasma sheath
106, wafer
104, chuck
112, coupling ring
108, edge ring
102, and ceramic ring
110 are as shown in FIG.
1. Beginning at the conducting surface of chuck
112, there is shown
an equivalent capacitance C
0, which is defined by the surface of chuck
112,
the surface of coupling ring
108, and the space in between. Along the capacitive
path
150, there is another equivalent capacitance
2 which is defined
by the surfaces of coupling ring
108 and the lower face of edge ring
102
and the space in between. Further along the capacitive path
150, the dielectric
material in edge ring
102 forms another capacitance C
1. Additionally,
the gap between plasma sheath
106 and the upper surface of edge ring
102
forms another capacitance Cs along capacitive path
150.
Referring now to FIG. 2B, a simplified electrical diagram for capacitive
path
150 is shown. Chuck
112 is electrically coupled in series with
capacitance C
0, which is shown disposed between chuck
112 and coupling
ring
108. Capacitance C
2 is coupled in series along the capacitive
path
150 between coupling ring
108 and the lower face of edge ring
102. Capacitance
1 which is formed by the dielectric material of
edge ring
102 is shown coupled in series with capacitance C
2. Capacitance
Cs completes the capacitive path
150 by coupling in series with capacitance
C
2 between capacitance C
2 and plasma sheath
106.
When the edge ring is worn away and/or damaged by the plasma, the capacitance
C
1 attributable to the dielectric material of the edge ring changes. The
change in capacitance C
1 in turn affects the plasma environment in the vicinity
of the damaged regions of the edge ring. As the plasma environment changes, process
result degrades.
FIG. 3A illustrates a simplified cross section view of the plasma processing
chamber of FIG. 2A, including an exemplary damaged region
304 in edge ring
102. It is believed that damaged region
304, which may take the form
of a trench, cavity, or pit in edge ring
102 alters the aforementioned capacitance
C
1 in the vicinity of the damaged region. The changed capacitive path is
shown in FIG.
3B. In contrast to the situation in FIG. 2B, the value of
the capacitance C
1′ attributable to the damaged dielectric material
in edge ring
102 is larger due to the thinning of the dielectric material
(since C=εA/d). This increase in the value of capacitance C
1 in turn
increases the total capacitance along capacitive path
150, contributing
to a reduction in the impedance along path
150 (since Z=1/ωC or Z=d/εAω).
As the impedance along the path from the plasma sheath to the chuck decreases,
the current along path
150 increases. This increase in the current between
the plasma sheath and the chuck through the damaged regions of the edge ring coincides
with an increase in the etch rate at the edge of the substrate, relative to other
regions of the substrate. In addition, the features etched in the edge areas of
the substrate show more tilt towards the substrate perimeter as the edge ring erosion
progresses. Ideally, there would be no change in substrate edge etch rate and no
tilting of the etched features over time. Also, the edge ring would either not
erode or erode at a slow rate which would allow the etcher to remain in service
until some later service interval was reached. Some semiconductor manufacturing
processes cannot tolerate the etching characteristics changing more than a very
small amount, and as such the edge ring lifetime is shortened more so than by the
mere loss of material. It is the purpose of this invention to effectively extend
the service life of the edge ring by compensating for the erosion so as to minimize
the substrate edge etch rate change and feature tilt effects with time.
In accordance with one aspect of the present invention, the change in the capacitance
along capacitive path
150 attributable to edge ring damage is compensated
for by reducing the capacitance of one or more of capacitances C
0, C
2
or CS. In a preferred embodiment, the increase in capacitance C
1 due to
edge ring thinning damage is offset by decreasing the capacitance C
2 associated
with the gap between the lower surface of the edge ring and the coupling ring.
In one embodiment, decreasing the capacitance C
2 is accomplished by providing
a mechanism that can move the edge ring and the coupling ring further apart to
decrease the capacitance C
2 in between to compensate for the increased capacitance
C
1 caused by edge ring thinning damage.
FIG. 4A illustrates, in accordance with one embodiment of the present invention,
a simplified cross section view of a plasma processing chamber with a variable
position coupling ring
408. Referring now to FIG. 4A, variable position
coupling ring
408 is configured to travel along a path
404. Since
the capacitance value of capacitance C
2 is dependent upon the distance between
lower surface of edge ring
102 and variable position coupling ring
408,
changing the position of variable position edge ring
408 will change the
capacitance value of capacitance C
2.
By using a variable position coupling ring, the increase in the capacitance C
1
associated with damaged edge ring
102 can now be offset by changing the
capacitance C
2 through the repositioning of variable position coupling ring
408 along path
404. The net result is that the total capacitance
along capacitance path
150 stays substantially the same, or is changed to
a lesser extent. Since the capacitance between the plasma sheath and the chuck
remains substantially unchanged or is changed to a lesser extent with the use of
a variable position coupling ring, the impedance between the plasma sheath and
the chuck stays substantially unchanged or is changed to a lesser extent as the
edge ring wears away. This in turn helps keep the plasma environment in the vicinity
of the damaged regions of the edge ring substantially unchanged or is changed to
a lesser extent as the edge ring wears away.
Furthermore, the use of a variable position coupling ring delays the
need to change the edge ring. As the edge ring wears away, the coupling ring is
repositioned to correct for process degradation. A point will still be reached
at which edge ring
102 will need to be replaced because of extensive structural
damage or because the increase in the capacitance C
1 due to edge ring damage
cannot be adequately compensated beyond some point by further decreasing one of
the other capacitances. However, replacement will occur less frequently than in
the prior art, thereby reducing both costly manufacturing down time as well as
the need for equipment recalibration necessitated by the replacement process.
In one embodiment, the amount of edge ring thinning or damage may be empirically
determined for a particular process in a particular plasma processing chamber by
measuring the edge ring thickness over time. For example, the thickness of the
edge ring in the affected regions may be measured using a contact probe, in one
embodiment. Once the amount of edge ring thinning is determined as a function of
time or as a function of the number of substrates processed, the capacitance value
C
1 as a function of time or as a function of the number of substrates processed
may be determined. This information may be used to determine the required decrease
in capacitance, as a function of time or as a function of the number of substrates
processed, in one or more of the other capacitances along the capacitive path between
the plasma sheath and the chuck in order to offset the increase in the capacitance
caused by edge ring thinning damage. In the variable position coupling ring case,
this information may in turn be employed to calculate the required gap during production
runs between the coupling ring and the edge ring, as a function of time or as a
function of the number of substrates processed, to satisfactorily offset the increase
in the capacitance caused by edge ring thinning damage.
In another embodiment, the decrease in the capacitance value of one or more of
the other capacitances along the capacitive path between the plasma sheath and
the chuck may be computed, either theoretically or via computer-assisted modeling
taken into account, among others, the materials of the various components of the
plasma processing chamber, the geometry of the chamber and its components, and
the process recipe. This information may then be employed to reduce the capacitance
of one or more of the other capacitances along the capacitive path between the
plasma sheath and the chuck in the production chamber.
Reducing the capacitance value of one or more of the other capacitances
along the capacitive path between the plasma sheath and the chuck through the edge
ring may be accomplished in various ways. In the case of a variable position coupling
ring, for example, one or more linear or screw actuators may be provided to physically
move variable position coupling ring
408 relative to the edge ring. The
actuator(s) may be anchored against chuck
112 or ceramic ring
110
or even edge ring
102 if desired.
Additionally, it is contemplated that the edge ring may alternately
or additionally be made movable to compensate for the increase in the capacitance
C
1 attributable to edge ring thinning damage. Still further, it is possible
to keep the coupling and edge rings stationary and provide movable inserts, which
can be positioned as needed in the gaps between the chuck and the coupling ring,
or in between the coupling ring and the edge ring, or in between the edge ring
and the plasma sheath, to offset the increase in the capacitance C
1 attributable
to edge ring thinning damage.
In any case, it is preferable that the capacitance adjustment be performed in-situ.
That is, it is preferable that there be a mechanism provided with the plasma processing
chamber to allow the capacitance of one or more of the other capacitances along
the capacitive path between the plasma sheath and the chuck to be adjusted without
the need to remove the plasma processing chamber from service on the production
line for an extended period of time. The actuator coupled to the variable position
coupling ring is but one example of this type of in-situ capacitance adjustment
mechanism to offset the increase in the capacitance C
1 attributable to edge
ring thinning damage. As a further example, the coupling ring may be made stationary
but may have a variable impedance to the chuck through the use of a variable impedance
device, such as a variable capacitor. In this case, the adjustment may be made
by adjusting the value of the variable impedance device as necessary to offset
the change in the capacitance of the edge ring.
It should also be understood that some chamber designs may include fewer or a
greater number of components in the capacitive path between the plasma sheath and
the chuck through the edge ring. Irrespective of the number of components (such
as rings or any other structures) involved, as long as one or more of the other
capacitances along the capacitive path between the plasma sheath and the chuck
body can be reduced to offset the increase in the capacitance C
1 attributable
to edge ring thinning damage, process degradation is reduced and the edge ring
can be employed for a longer period of time before requiring a replacement.
While this invention has been described in terms of several preferred embodiments,
there are alterations, permutations, and equivalents which fall within the scope
of this invention. For example, although the drawings are described in the context
of an etching application, it should be understood that the invention also applies
to deposition processes. In the case of a deposition process, or even for certain
etch processes, the deposition of material on the edge ring may decrease the capacitance
of the edge ring along the aforementioned capacitive path between the plasma sheath
and the chuck body, and in some cases, require an adjustment that increases the
capacitance elsewhere along the capacitive path to compensate. In this case, the
amount of deposition over time may be empirically determined to ascertain the change
in the capacitance of the edge ring due to the deposition, or the change in the
capacitance of the edge ring may be modeled or mathematically computed. This information
may then be employed to facilitate compensation by adjusting one or more capacitances
along the aforementioned capacitive path.
Furthermore, it is not necessary that the invention be limited to any
particular type of plasma generation technology. Accordingly, it is contemplated
that the invention applies to any and all plasma processing systems that experience
process degradation due to edge ring thinning damage or the buildup of material
on the edge ring, irrespective of how the plasma is generated, including inductively
coupled plasma processing systems, capacitively coupled plasma processing systems,
and others. It should also be noted that there are many alternative ways of implementing
the methods and apparatuses of the present invention. It is therefore intended
that the following appended claims be interpreted as including all such alterations,
permutations, and equivalents as fall within the true spirit and scope of the present invention.
*
