U.S. patent application number 10/325203 was filed with the patent office on 2003-05-15 for method of modifying an rf circuit of a plasma chamber to increase chamber life and process capabilities.
Invention is credited to Blalock, Guy, Donohoe, Kevin G..
Application Number | 20030089681 10/325203 |
Document ID | / |
Family ID | 21753641 |
Filed Date | 2003-05-15 |
United States Patent
Application |
20030089681 |
Kind Code |
A1 |
Blalock, Guy ; et
al. |
May 15, 2003 |
Method of modifying an RF circuit of a plasma chamber to increase
chamber life and process capabilities
Abstract
A method for controlling the voltage distribution of the
standing wave impressed upon the coil of an inductively coupled
plasma generator includes the steps of impressing a radio frequency
voltage across the coil to establish a standing wave thereacross. A
voltage profile is selected for the standing wave so as to control
the location and amount of capacitive coupling. A circuit parameter
is controlled to achieve the selected voltage profile. Proper
selection of the voltage profile enhances process capabilities,
decreases the time between cleans, minimizes component wear, and
minimizes cleaning time. An apparatus for carrying out the
disclosed method is also disclosed.
Inventors: |
Blalock, Guy; (Boise,
ID) ; Donohoe, Kevin G.; (Boise, ID) |
Correspondence
Address: |
THORP REED & ARMSTRONG, LLP
ONE OXFORD CENTRE
301 GRANT STREET, 14TH FLOOR
PITTSBURGH
PA
15219-1425
US
|
Family ID: |
21753641 |
Appl. No.: |
10/325203 |
Filed: |
December 20, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10325203 |
Dec 20, 2002 |
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09613325 |
Jul 7, 2000 |
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6503410 |
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09613325 |
Jul 7, 2000 |
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09012155 |
Jan 22, 1998 |
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6095159 |
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Current U.S.
Class: |
216/68 ; 427/569;
438/714; 438/788 |
Current CPC
Class: |
Y10S 438/905 20130101;
H01J 37/321 20130101; H01J 37/32174 20130101 |
Class at
Publication: |
216/68 ; 427/569;
438/714; 438/788 |
International
Class: |
C23F 001/00; C03C
025/68; H01L 021/461 |
Claims
What is claimed is:
1. A method, comprising: impressing a radio frequency voltage
across a coil to establish a standing wave thereacross; selecting a
voltage profile for said standing wave so as to control the
location and amount of capacitive coupling; and controlling a
circuit parameter to achieve said selected voltage profile.
2. The method of claim 1 wherein said step of controlling a circuit
parameter includes the step of controlling the value of one of a
capacitor and an inductor connected between an end of the coil and
ground.
3. The method of claim 1 wherein said step of selecting said
voltage profile incudes the step of selecting a voltage profile so
as to achieve maximum capacitive coupling at a point where maximum
cleaning is desired.
4. A method of controlling the voltage impressed across an
inductive coil of a plasma chamber during processing of items to
optimize cleaning efficiency during a subsequent cleaning cycle,
comprising: impressing a radio frequency voltage across a coil to
establish a standing wave thereacross; selecting a voltage profile
for said standing wave so as to achieve optimum polymer deposition
during processing of an item at a location where cleaning can be
achieved most efficiently; and controlling a circuit parameter to
achieve said selected voltage profile.
5. The method of claim 4 wherein said step of controlling a circuit
parameter includes the step of controlling the value of one of a
capacitor and an inductor connected between an end of the coil and
ground.
6. The method of claim 4 wherein the processing of items includes
performing an etch step on solid state devices.
7. The method of claim 4 wherein the processing of items includes
performing a deposition step on solid state devices.
8. The method of claim 4 wherein said voltage profile selected for
the processing of items is different from the voltage profile
selected during the subsequent cleaning cycle.
9. A method of controlling the voltage impressed across an
inductive coil of a plasma chamber during a cleaning cycle,
comprising: impressing a radio frequency voltage across a coil to
establish a standing wave thereacross; selecting a voltage profile
for said standing wave so as to control a location where maximum
cleaning is to occur; and controlling a circuit parameter to
achieve said selected voltage profile.
10. The method of claim 9 additionally comprising the step of
varying the voltage profile during the cleaning cycle.
11. The method of claim 10 wherein said step of varying the voltage
profile includes the step of varying the voltage profile in a
stepwise manner.
12. The method of claim 10 wherein said step of varying the voltage
profile includes the step of varying the voltage profile in a
continuous manner.
13. The method of claim 9 wherein said step of controlling a
circuit parameter includes the step of controlling the value of one
of a capacitor and an inductor connected between an end of the coil
and ground.
14. An apparatus, comprising: a radio frequency generator; a coil
having a first end connected to said radio frequency generator and
a second end; and a component having an adjustable value, said
component connected between said second end of said coil and ground
whereby adjusting the value of said component enables the selection
of a voltage profile for a standing wave set up across said coil by
said generator.
15. The apparatus of claim 14 wherein said component includes a
variable capacitor.
16. The apparatus of claim 14 wherein said component includes a
variable inductor.
17. The apparatus of claim 14 additionally comprising a matching
circuit connected between said generator and said first end of said
coil.
18. A plasma processing apparatus, comprising: a chamber; a gas
handling system servicing said chamber; a wafer handling system
servicing said chamber; a radio frequency generator; a coil having
a first end connected to said radio frequency generator and a
second end, said coil being located so as to radiate energy into
said chamber and generate a plasma; and a component having an
adjustable value, said component connected between said second end
of said coil and ground whereby adjusting the value of said
component controls a standing wave impressed along said coil.
19. The apparatus of claim 18 wherein said component includes a
variable capacitor.
20. The apparatus of claim 18 wherein said component includes a
variable inductor.
21. The apparatus of claim 18 additionally comprising a matching
circuit connected between said generator and said coil.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention is directed generally to plasma
processing chambers and, more particularly, to inductively coupled
processing chambers.
[0003] 2. Description of the Background
[0004] Plasma processing chambers are used in a number of different
industries. For example, plasma processing chambers are used in the
fabrication of integrated circuits, for coating medical devices,
and for coating mirrors. Plasma processing chambers may be either
inductively coupled or capacitively coupled. In the capacitively
coupled systems, electrodes comprised of parallel plates are
energized to produce the plasma. In the inductively coupled
systems, an inductive coil is energized to produce the plasma. In
both systems, varying the parameters of the mechanism used to
generate the plasma provides some ability to control the
characteristics of the generated plasma.
[0005] For example, in inductively coupled systems, the coil has a
time varying radio frequency voltage impressed thereupon. The
electron heating zone in the inductively coupled plasma is shaped
like a torroid whose diameter is affected by the coil geometry. The
value of the capacitor between the coil and ground may also effect
the size and location of the electron heating zone.
[0006] In the semiconductor industry, a plasma chamber may be used
to carry out a variety of processes such as etching, deposition,
sputtering, and annealing. Many of those processes leave
contaminant depositions throughout the processing chamber. Such
contaminants may adversely impact the process step being performed
which, in turn, can adversely impact device yield. The adverse
impact on device yield becomes more pronounced as device size
decreases.
[0007] Another problem is the wear out of the dielectric parts (the
plate) within the processing chamber. Wear out of the plate is a
particular problem when the chamber is used for etching. For
example, an etching process can result in the deposition of a
polymer on the plate. A cleaning step is required to remove that
polymer. The efficacy of the cleaning step depends on a number of
parameters, one of which is the value of the capacitive coupling
between the coil and plasma. That capacitive coupling is defined by
a voltage standing wave present on the inductive coil while
powered. The higher the voltage, the greater the capacitive
coupling. The cleaning efficacy at different radial and azimuthal
locations on the parts varies with the value of the capacitive
coupling. Also, the wear out of the plate is concentrated in one
location determined by the value of the capacitive coupling.
[0008] Because of the need to keep expensive process equipment such
as plasma chambers in service, it is desirable to operate the
plasma chamber in a way which improves process capability,
minimizes part wear, reduces time between cleans, and minimizes
cleaning time. Thus, the need exists for a method and apparatus
which achieves those goals.
SUMMARY OF THE INVENTION
[0009] The present invention solves the problems encountered in the
prior art by controlling the voltage distribution of the standing
wave impressed upon the coil, thereby controlling the location and
amount of capacitive coupling. In the presently preferred
embodiment, that is accomplished by controlling the value of the
capacitor in the RF circuit between the coil and ground.
Controlling the value of the coil to ground capacitor during an
etching step controls the location of the deposit that occurs
during an etching process. The capacitor can be fixed at an optimal
value or varied from the beginning of the etch process (where the
capacitor's value may be less important) to the end (where the
capacitor's value can be very important). That permits the more
critical end of the etch to occur in an optimally shaped electron
heating zone and in a chamber that has an optimal deposition
pattern of the polymer resulting from the capacitor value during
the early portion of the step.
[0010] The invention also contemplates changing the value of the
capacitor from the etch to the clean step and changing the value of
the capacitor during the clean step. Changing the value of the
capacitor during the clean step makes that step more efficient and
eliminates the concentration of wear in one place. The value of the
coil to ground capacitor may be changed stepwise or continuously
during the etch step or the clean step.
[0011] More broadly, the present invention is directed to a method
comprised of the steps of:
[0012] impressing a radio frequency voltage across a coil to
establish a standing wave thereacross;
[0013] selecting a voltage profile for the standing wave so as to
achieve optional capacitive coupling of at at least one
predetermined position across the coil; and
[0014] controlling a circuit parameter, such as the value of a
capacitor or inductor, to achieve the selected voltage profile.
[0015] An apparatus for carrying out the method is also disclosed.
By controlling the voltage distribution of the standing wave,
process capabilities are enhanced, the time between cleans is
maximized, component wear is minimized, and cleaning time is
minimized. Those advantages and benefits of the present invention,
and others, will become apparent from the Description of the
Preferred Embodiments hereinbelow.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] For the present invention to be clearly understood and
readily practiced, the present invention will be described in
conjunction with the following figures wherein:
[0017] FIG. 1 is a diagram illustrating certain of the components
of a plasma processing apparatus with which the present invention
may be used;
[0018] FIG. 2 is an electrical schematic illustrating the apparatus
of the present invention; and
[0019] FIG. 3 is a flow chart illustrating the steps of the method
of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] FIG. 1 illustrates a plasma processing apparatus 10 with
which the present invention may be used. It is to be understood
that the apparatus 10 has been simplified to illustrate only those
components which are relevant to an understanding of the present
invention. Those of ordinary skill in the art will recognize that
other components are required to produce an operational processing
apparatus 10. However, because such components are well known in
the art, and because they do not further aid in the understanding
of the present invention, a discussion of such components is not
provided.
[0021] In FIG. 1, the apparatus 10 may be comprised of a cold wall
reaction chamber 12 constructed of aluminum. The bottom and sides
of the reaction chamber 12 may be lined with quartz to protect the
walls from film deposition during the processing steps. The walls
of the chamber 12 may be cooled by a circulating water jacket (not
shown) in conjunction with a heat exchanger (not shown). The walls
are typically maintained at or above 100.degree. C., because lower
temperatures may induce the deposition of films on the walls of the
reaction chamber 12. Such depositions can be undesirable because
they remove etchant from the plasma and result in material which
must be eventually cleaned from the surface to maintain
productivity of the chamber. Such depositions may cause temperature
gradients which adversely affect the processing steps and alter the
stability of processing chemistries. Furthermore, depositions on
walls may flake and produce particulate that can contaminate a
wafer in the chamber 12.
[0022] A wafer support table 14 or the like is located near the
bottom of the chamber 12, and is used for supporting a wafer 16.
The support table 14 is a flat surface, typically having three or
more vertical support pins 15 with low thermal mass.
[0023] A wafer handling system 18 is adjacent to the chamber 12,
and includes a wafer cassette 20 and a wafer handling robot 22. The
wafer cassette 20 holds a plurality of wafers, and the wafer
handling robot 22 transports one wafer at a time from the wafer
cassette 20 to the wafer support table 14, and back again. A door
24 isolates the wafer handling system 18 from the chamber 12 when
the wafers are not being transported to and from the wafer support
table 14.
[0024] A gas source 26 is in fluid communication with the chamber
12. More than one type of gas may be available from gas source 26,
and gases may be provided individually or in combination. The gases
may, for example, be used to deposit films on the wafer 16, flush
gases from the chamber 12, or cool the chamber 12 and the wafer
16.
[0025] Gases are removed from the chamber 12, and a vacuum may be
created within the chamber 12, by a gas exhaust and vacuum system
28, as is well known in the art. Also present are sensors 30, such
as a pyrometer, which are used to measure process parameters.
[0026] A power supply 32 supplies power to a coil 34 connected to
ground through a variable capacitor 36. The coil 34 is a flat
spiral coil that is positioned proximate to a window 38 in the
chamber 12. The position of the coil 34 and the material comprising
the window 38 are selected as is known in the art such that RF
energy produced by the coil 34 is efficiently coupled to the gases
in the chamber 12 to produce a plasma 40.
[0027] The electron heating zone in the inductively coupled plasma
40 is shaped like a torroid whose diameter is effected by the
coil's 34 geometry. The size of the heating zone and its location
relative to the wafer have important effects on the process
results. In addition, the deposition thickness of polymer on the
window 38 varies with radial and azimuthal position in a way that
depends on the value of the capacitor 36.
[0028] Completing the description of FIG. 1, a control computer 42
controls the various components which comprise the plasma
processing apparatus 10.
[0029] In FIG. 2, an electrical schematic illustrating the
apparatus of the present invention is illustrated. The power supply
32 of FIG. 1 is illustrated in FIG. 2 as an RF generator 44. The RF
generator 44 supplies power to the coil 34 through a matchbox
circuit 46. The matchbox circuit 46 is known in the art and is used
for impedance matching to ensure maximum coupling of power from the
RF generator 44 to the coil 34. As seen in FIG. 2, the coil 34 is
connected at a first end 47 to the RF generator 44 through the
matchbox circuit 46 and is connected at a second end 48 to ground
through a variable component 50. In the preferred embodiment of the
present invention, the variable component 50 may be the variable
capacitor 36 as shown in FIG. 1.
[0030] In operation, the RF generator 44 is used to impress a radio
frequency voltage across the coil 34. As is known in the art, that
causes a standing wave to be created across the coil 34. By
graphing the magnitude of the voltage as a function of coil length,
a voltage profile can be generated. By varying the value of the
variable component 50, that voltage profile can be varied. The
advantage of varying the voltage profile is that it varies where
the point or points of maximum or minimum voltage appear across the
coil 34. The points of maximum voltage correspond to areas of
maximum capacitive coupling to the plasma whereas the points of
minimum voltage correspond to areas of minimum capacitive coupling
to the plasma. "Capacitive coupling to the plasma" refers to the
region under the coil in the plasma where the voltage on the coil
is high enough to cause capacitive etching. That is etching with a
sputter component. That is the type of etching that is most
efficient to keep a surface clean. By varying these areas of
maximum and minimum coupling to the plasma, various desirable
characteristics can be obtained as described more fully
hereinbelow.
[0031] FIG. 3 is a flowchart illustrating the steps of the method
of the present invention. One aspect of the present invention is
illustrated by block 56. Block 56 represents the step in the
process wherein the value of the variable component 50 is selected
so that contaminant polymer depositions will be deposited on window
38 in locations wherein it will be the easiest to clean with
subsequent cleaning steps. Thereafter, the apparatus 10 is used for
its desired purpose.
[0032] Step 56 also contemplates that the value of the variable
component 50 may be changed during the process step. For example,
the value of the variable component 50 may be fixed at a first
value during the beginning of a process such as an etch process.
The value of the variable component 50 may be selected so as to
produce a desirable deposition pattern. Thereafter, later in the
etch process, the value of the variable component 50 may be changed
so as to produce an optimally shaped electron heating zone in the
chamber 12 that has an optimal deposition pattern of the polymer
resulting from the earlier value of the variable component 50.
[0033] The present invention also contemplates changing the value
of the variable component 50 from the process step to the clean
step as shown by block 58 in FIG. 3. According to that aspect of
the present invention, the voltage profile of the standing wave
impressed upon the coil 34 is adjusted so as to locate regions of
maximum capacitive coupling proximate to those regions of the
window 38 which require the most cleaning. Thereafter, the clean
cycle is run at step 60.
[0034] The present invention also contemplates changing the value
of the variable component 50 during the clean step. That is, after
the contaminant polymer begins to be removed from the window 38, it
will be removed first from those areas having maximum capacitive
coupling. After those areas are clean, it is desirable to relocate
the area of maximum capacitive coupling to those portions of the
window 38 which are not yet clean. That may be accomplished by
either continually varying the value of the variable component 50
or varying the value of the variable component 50 in a step-wise
manner.
[0035] By controlling the voltage distribution of the standing
wave, process capabilities are enhanced, the time between cleanings
is maximized, component wear is minimized, and the cleaning time is
minimized as discussed above.
[0036] While the present invention has been described in
conjunction with preferred embodiments thereof, many modifications
and variations will be apparent to those of ordinary skill in the
art. The foregoing description and the following claims are
intended to cover all such modifications and variations.
* * * * *