U.S. patent application number 09/329020 was filed with the patent office on 2001-06-14 for substrate support for plasma processing.
Invention is credited to CHAFIN, MICHAEL G., DAHIMENE, MAHMOUD, GRIMARD, DENNIS S., KUMAR, ANANDA H., SALIMIAN, SIAMAK, SHAMOUILIAN, SHAMOUIL.
Application Number | 20010003298 09/329020 |
Document ID | / |
Family ID | 23283511 |
Filed Date | 2001-06-14 |
United States Patent
Application |
20010003298 |
Kind Code |
A1 |
SHAMOUILIAN, SHAMOUIL ; et
al. |
June 14, 2001 |
SUBSTRATE SUPPORT FOR PLASMA PROCESSING
Abstract
A support 55 comprises a dielectric 60 covering a primary
electrode 70, the dielectric 60 having a surface 75 adapted to
receive a substrate 25 and a conduit 160 that extends through the
dielectric 60. The thickness of a portion of the dielectric 60
between an edge 195 of the primary electrode 70 and a surface 180
of the conduit 160 is sufficiently large to reduce the incidence of
plasma formation in the conduit 160 when the primary electrode 70
is charged by an RF voltage to form a plasma of gas in the chamber
30 during processing of the substrate 25.
Inventors: |
SHAMOUILIAN, SHAMOUIL; (SAN
JOSE, CA) ; KUMAR, ANANDA H.; (MILPITAS, CA) ;
SALIMIAN, SIAMAK; (SUNNYVALE, CA) ; DAHIMENE,
MAHMOUD; (GAITHERSBURG, MD) ; CHAFIN, MICHAEL G.;
(SAN JOSE, CA) ; GRIMARD, DENNIS S.; (ANN ARBOR,
MI) |
Correspondence
Address: |
PATENT COUNSEL
APPLIED MATERIALS INC
PO BOX 450 A
SANTA CLARA
CA
95052
|
Family ID: |
23283511 |
Appl. No.: |
09/329020 |
Filed: |
June 9, 1999 |
Current U.S.
Class: |
156/345.43 ;
118/500; 118/723R; 118/728; 156/345.51 |
Current CPC
Class: |
H01J 2237/2007 20130101;
H01L 21/67069 20130101; H01L 21/6831 20130101; H01J 37/32697
20130101; H01J 37/32559 20130101 |
Class at
Publication: |
156/345 ;
118/723.00R; 118/728; 118/500 |
International
Class: |
C23C 016/458 |
Claims
What is claimed is:
1. A support capable of supporting a substrate and forming a plasma
of a gas in a chamber, the support comprising: (a) a primary
electrode that is chargeable to form the plasma of the gas in the
chamber; and (b) a dielectric covering the primary electrode, the
dielectric having a surface adapted to receive the substrate, and
the dielectric having a conduit extending therethrough, a thickness
of a portion of the dielectric between the primary electrode and
the conduit being sufficiently large to reduce plasma formation in
the conduit.
2. A support according to claim 1 wherein the conduit is adapted to
provide heat transfer gas to the surface of the dielectric.
3. A support according to claim 1 wherein the conduit is adapted to
hold a lift pin adapted to lift and lower the substrate.
4. A support according to claim 1 wherein the thickness of the
portion of the dielectric between the primary electrode and the
conduit is from about 2 times to about 200 times a thickness of
dielectric that overlies the primary electrode.
5. A support according to claim 1 wherein the thickness of the
portion of the dielectric between the primary electrode and the
conduit is at least about 3 mm.
6. A support according to claim 4 wherein the thickness of the
portion of the dielectric between the primary electrode and the
conduit is less than about 10 mm.
7. A support according to claim 1 wherein the dielectric comprises
a ceramic monolith.
8. A support according to claim 1 further comprising a secondary
electrode covered by the dielectric.
9. A support according to claim 8 wherein the secondary electrode
is not in the same plane as the primary electrode.
10. A support according to claim 8 wherein the secondary electrode
is below the primary electrode.
11. A support according to claim 8 wherein the secondary electrode
comprises a perimeter adjacent to an edge of the primary
electrode.
12. A support according to claim 8 wherein the secondary electrode
comprises a collar disposed adjacent to a portion of the primary
electrode.
13. A support according to claim 8 wherein the secondary electrode
is smaller than the primary electrode.
14. A chamber comprising the support of claim 1, the chamber
comprising: (a) gas distributor; and (b) an exhaust, whereby a
substrate held on the support is processed by a plasma of gas
distributed by gas distributor and exhausted by the exhaust.
15. A support capable of supporting a substrate during plasma
processing in a chamber, the support comprising: (a) first means
for receiving the substrate and providing a first gas below the
substrate; and (b) second means for forming a plasma of second gas
above the substrate and for reducing plasma formation in the first
gas in the conduit during processing of the substrate on the
support in the chamber.
16. A support according to claim 15 wherein the first means
comprises a dielectric covering a primary electrode, and the second
means comprises a thickness of a portion of a dielectric between an
edge of the primary electrode and the conduit that is sufficiently
large to reduce plasma formation in the first gas in the
conduit.
17. A support according to claim 16 wherein the second means
comprises a secondary electrode covered by a dielectric.
18. A support for supporting a substrate in a chamber, the support
comprising: (a) a dielectric having a surface adapted to receive
the substrate, the dielectric comprising a conduit; (b) a primary
electrode covered by the dielectric, the primary electrode being
chargeable to form a plasma of gas in the chamber, and the primary
electrode having an edge around the conduit; and (c) a secondary
electrode covered by the dielectric.
19. A support according to claim 18 wherein the secondary electrode
is adapted to suppress coupling of energy from the edge of the
primary electrode to gas in the conduit during processing of the
substrate on the support in the chamber.
20. A support according to claim 18 wherein the secondary electrode
is not in the same plane as the primary electrode.
21. A support according to claim 18 wherein the secondary electrode
is below the primary electrode.
22. A support according to claim 18 wherein the secondary electrode
comprises a perimeter adjacent to the edge of the primary
electrode.
23. A support according to claim 18 wherein the secondary electrode
comprises a collar disposed about a portion of the primary
electrode.
24. A support according to claim 18 wherein the secondary electrode
is smaller than the primary electrode.
25. A support according to claim 18 wherein a thickness of a
portion of the dielectric between the conduit and the edge of the
primary electrode is sufficiently large to reduce the plasma
formation in the gas in the conduit during processing of the
substrate in the chamber.
26. A method of fabricating a support for holding a substrate in a
chamber, the method comprising the steps of forming a dielectric
covering a primary electrode, and forming a conduit in the
dielectric so that a thickness of a portion of the dielectric
between an edge of the primary electrode and a surface of the
conduit is sufficiently large to reduce the incidence of plasma
formation in the conduit when the primary electrode is charged by
an RF voltage during processing of the substrate in the
chamber.
27. A method according to claim 26 wherein the step of forming a
dielectric covering a primary electrode comprises the step of
forming a dielectric comprising a monolith having the primary
electrode therein.
28. A method according to claim 26 comprising the step of forming a
primary electrode having an area sufficiently large to
electrostatically attract and hold the substrate upon application
of a DC voltage to the primary electrode.
29. A method of fabricating a support for holding a substrate in a
chamber, the method comprising the steps of forming a dielectric
comprising a conduit, the dielectric covering a primary electrode
and a secondary electrode, the primary electrode being chargeable
to sustain a plasma of gas in the chamber, and the secondary
electrode being shaped and sized to suppress coupling of energy
from the edge of primary electrode to gas in the conduit during
processing of the substrate on the support in the chamber.
30. A method according to claim 29 comprising the step of forming a
secondary electrode having a perimeter extending along the edge of
the primary electrode.
31. A method according to claim 29 comprising the step of forming a
secondary electrode that is not in the same plane as the primary
electrode.
32. A method according to claim 29 comprising the step of forming a
secondary electrode having an area that is smaller than an area of
the primary electrode.
33. A chamber for processing a substrate, the chamber comprising:
(a) a gas distributor capable of providing gas into the chamber;
(b) a dielectric having a surface capable of receiving the
substrate and having a conduit therethrough; (c) a primary
electrode and a secondary electrode below the dielectric; and (d) a
voltage supply adapted to charge the primary electrode with an RF
potential to sustain a plasma of gas in the chamber, and
electrically bias the secondary electrode relative to the primary
electrode to reduce plasma formation in the conduit during
processing of the substrate in the chamber.
34. A chamber according to claim 33 wherein the secondary electrode
is electrically grounded.
35. A chamber according to claim 33 wherein the secondary electrode
is not in the same plane as the primary electrode.
36. A chamber according to claim 33 wherein the secondary electrode
is smaller than the primary electrode.
37. A chamber according to 33 wherein the voltage supply further
comprises a DC voltage source and wherein the primary electrode is
chargeable to electrostatically attract and hold the substrate upon
application of a DC voltage to the primary electrode.
38. A method of processing a substrate placed on a support in a
chamber, the support comprising a dielectric having a surface
capable of receiving the substrate, the dielectric covering a
primary electrode and a secondary electrode, and the dielectric
having a conduit therethrough, the method comprising the steps of:
(a) placing the substrate on the surface of the dielectric; (b)
maintaining the primary electrode in the support at an RF potential
to sustain a plasma of gas in the chamber; and (c) electrically
biasing the secondary electrode relative to the primary electrode
to reduce plasma formation in the conduit during processing of the
substrate in the chamber.
39. A method according to claim 38 wherein step (c) comprises the
step of electrically grounding the secondary electrode.
40. A method according to claim 38 further comprising the step of
applying a DC potential to the primary electrode in the support to
electrostatically hold the substrate to the dielectric.
Description
BACKGROUND
[0001] The invention relates to a support for supporting a
substrate during plasma processing in a chamber.
[0002] Integrated circuits are fabricated by placing a substrate on
a support in a chamber, introducing gas into the chamber, and
energizing the gas by coupling RF energy to the gas to form a
plasma. The support typically comprises dielectric covering an
electrode. The gas in the chamber is energized by applying an RF
voltage to the electrode and electrically grounding a facing
conductor surface in the chamber. The support comprises one or more
conduits that extend through the dielectric and electrode, such as
gas conduits for supplying heat transfer gas to the interface
between the substrate and the dielectric, and other conduits to
hold lift-pins that raise or lower the substrate onto the support.
It is desirable to extend the edge or extremity of the electrode in
the support as close as possible to the conduits to allow a
relatively uniform level of RF energy to be coupled to the
overlying plasma--even across the electrode gap created by the
conduits. However, the proximity of the edge of the electrode to
the conduit can result in electrical coupling of the RF energy from
the electrode edge to the gas in the conduit. This RF coupling
leads to ionization, arcing, and glow discharge of the gas in the
conduit. This is undesirable because it causes sputtering, chemical
erosion and thermal degradation of the conduit surfaces, the
support, and even the backside of the overlying substrate.
[0003] Plasma formation in conduits is especially a problem for
ceramic dielectric supports. Ceramic supports made from alumina are
being increasingly used due to their resistance to chemical erosion
and their ability to withstand high temperatures. However, such
ceramic supports typically have large diameter conduits because it
is difficult to machine small diameter conduits in the brittle
ceramic material. A conduit having a large diameter provides a
longer pathway in the gap of the conduit for the acceleration of
ionized gas molecules. The longer pathway results in a larger
number of energetic collisions between charged gas species and
other gas molecules which results in avalanche breakdown and plasma
formation in the conduit.
[0004] Thus there is a need for a support that reduces the
incidence of arcing, glow discharge, or plasma formation in
conduits that extend through the support during processing of a
substrate in the chamber. There is also a need for a support that
exhibits reduced erosion and thermal degradation in the chamber. It
is further desirable to have a support that provides a more uniform
plasma sheath across the surface of the substrate.
SUMMARY
[0005] The present invention satisfies these needs by providing a
support capable of supporting a substrate and forming a plasma of a
gas in a chamber. The support comprises a primary electrode that is
chargeable to form the plasma of the gas in the chamber. A
dielectric covers the primary electrode, the dielectric having a
surface adapted to receive the substrate and a conduit extending
therethrough. A thickness of dielectric between the primary
electrode and the conduit is sufficiently large to reduce plasma
formation in the conduit. The support is particularly useful in a
chamber comprising a gas distributor and an exhaust, in which a
substrate held on the support is processed by a plasma of gas that
is distributed by the gas distributor and exhausted by the
exhaust.
[0006] In another version, the present invention is related to a
support comprising first means for receiving the substrate and
providing a first gas below the substrate, and second means for
forming a plasma of second gas above the substrate and for reducing
plasma formation in the first gas in the conduit during processing
of the substrate on the support in the chamber.
[0007] In yet another version, the present invention is related to
a support comprising a dielectric having a surface adapted to
receive the substrate and a conduit. A primary electrode is covered
by the dielectric, the primary electrode being chargeable to form a
plasma of gas in the chamber, and having an edge around the
conduit. A secondary electrode is also covered by the dielectric.
Preferably, the secondary electrode is adapted to suppress coupling
of energy from the edge of the primary electrode to gas in the
conduit during processing of the substrate on the support in the
chamber.
[0008] In still another version, the present invention is directed
to a substrate processing chamber comprising a gas distributor
capable of providing gas into the chamber, a dielectric having a
surface capable of receiving the substrate and having a conduit
therethrough, a primary electrode and a secondary electrode below
the dielectric; and a voltage supply adapted to charge the primary
electrode with an RF potential to sustain a plasma of gas in the
chamber, and electrically bias the secondary electrode relative to
the primary electrode to reduce plasma formation in the conduit
during processing of the substrate in the chamber.
[0009] In another aspect, the present invention is related to a
method of fabricating a support for holding a substrate in a
chamber. The method comprising the steps of forming a dielectric
covering an electrode, and forming a conduit in the dielectric so
that a thickness of dielectric between an edge of the electrode and
a surface of the conduit is sufficiently large to reduce plasma
formation in the conduit when the electrode is charged by an RF
voltage during processing of the substrate in the chamber.
[0010] In yet another aspect, the present invention is to a method
of fabricating the support by the steps of forming a dielectric
comprising a conduit, the dielectric covering a primary electrode
and a secondary electrode. The primary electrode is chargeable to
sustain a plasma of gas in the chamber and the secondary electrode
is shaped and sized to suppress coupling of energy from the edge of
the electrode to gas in the conduit during processing of the
substrate on the support in the chamber.
[0011] The present invention is also directed to a method of
processing a substrate on a support in a chamber, the support
comprising a dielectric having a surface capable of receiving the
substrate, the dielectric covering a primary electrode and a
secondary electrode and comprising a conduit that extends
therethrough. In the method, the substrate is placed on the surface
of the dielectric and the primary electrode in the support is
maintained at an RF potential to sustain a plasma of gas in the
chamber. The secondary electrode is electrically biased relative to
the primary electrode to reduce plasma formation in the conduit
during processing of the substrate in the chamber. Preferably, the
step of electrically biasing the secondary electrode comprises the
step of electrically grounding the secondary electrode.
DRAWINGS
[0012] These features, aspects, and advantages of the present
invention will become better understood with regard to the
following description, appended claims, and accompanying drawings
which illustrate examples of the invention, where:
[0013] FIG. 1 is a schematic sectional side view of a chamber
comprising a support according to the present invention;
[0014] FIG. 2a is a schematic sectional side view of a support
comprising a dielectric covering a primary electrode and having
conduits;
[0015] FIG. 2b is a schematic plan view of the support of FIG. 2a
showing the shape of the primary electrode and the dielectric
separating the conduits from the primary electrode;
[0016] FIG. 3 is a schematic sectional side view of another version
of a support comprising a dielectric covering a primary electrode
and a secondary electrode that is shaped and sized to suppress
coupling of RF energy from an edge of the primary electrode to gas
in a conduit;
[0017] FIG. 4 is a schematic sectional side view of a support
having a secondary electrode comprising a collar about an edge of a
primary electrode;
[0018] FIG. 5a is a schematic side view of a support having a
plurality of secondary electrodes comprising collars positioned
around each conduit;
[0019] FIG. 5b is a schematic sectional top view of the support
FIG. 5a;
[0020] FIG. 6 is a schematic sectional side view of another version
of a support showing a secondary electrode comprising a plurality
of collars;
[0021] FIG. 7 is a schematic sectional side view of a version of a
support showing a secondary electrode comprising a cylindrical
collar below and adjacent to a perimeter of an edge of a primary
electrode around a conduit;
[0022] FIG. 8 is a schematic sectional side view of another version
of the cylindrical collar of FIG. 7;
[0023] FIG. 9 is a graph of equipotential lines for a conventional
support comprising a primary electrode having an edge located 2.5
mm from a surface of a conduit;
[0024] FIG. 10 is a graph of equipotential lines for a support
according to the present invention in which a thickness of
dielectric between an edge of a primary electrode and a surface of
a conduit is about 4 mm;
[0025] FIG. 11 is a graph of equipotential lines for a support
according to the present invention having a primary electrode in
which a thickness of dielectric between an edge of a primary
electrode and a surface of a conduit is about 6 mm;
[0026] FIG. 12 is a graph of equipotential lines for a support
according to the present invention having a primary electrode and a
secondary electrode adapted to attract an electric field emanating
from an edge of a charged primary electrode; and
[0027] FIG. 13 is a graph of equipotential lines for a support
according to the present invention having a primary electrode and a
secondary electrode comprising a plurality of electrode
segments.
DESCRIPTION
[0028] FIG. 1 illustrates an apparatus 20 for processing a
substrate 25, such as a semiconductor wafer, in an energized gas or
plasma. Generally, the apparatus 20 comprises an enclosed chamber
30 having sidewalls 35, upper walls 45 and a bottom portion 50 on
which rests a support 55 for holding the substrate 25. The support
55 comprises a dielectric 60 covering a primary electrode 70, the
dielectric 60 having a surface 75 for receiving the substrate 25
thereon. Process gas (or first gas) from a gas supply 82 is
introduced into the chamber 30 through a gas distributor 80 having
a plurality of nozzles 85 that are distributed around the substrate
25. The gas is energized to form a plasma by inductively or
capacitively coupling RF energy into the chamber 30. For example,
the gas can be energized capacitively by applying an RF voltage
from a voltage supply 95 between the primary electrode 70 in the
support 55 and a partially facing conducting upper wall 45 of the
chamber 30. The apparatus 20 also includes an inductor coil 100
adjacent to the chamber 30 that is powered by a coil power supply
105 to inductively couple RF energy into the chamber 30. Typically
the frequency of the RF power applied to the primary electrode 70
and to the inductor coil 100 is from about 50 kHz to about 60 MHZ.
The RF power applied to the primary electrode 70 is typically from
about 10 to about 5000 Watts and the RF power applied to the
inductor coil 100 is typically from about 750 to about 5000 Watts.
Spent gas and byproducts are exhausted from the chamber 30 through
an exhaust system 110 which typically includes a vacuum pump 120
and a throttle valve 125 to control the pressure of gas in the
chamber 30.
[0029] Generally, the support 55 further comprises a base 130 for
supporting the dielectric 60. Preferably, the base 130 comprises
channels 135 through which heat transfer fluid is circulated to
heat or cool the substrate 25. More preferably, the base 130 is
shaped and sized to match the shape and size of the substrate 25
held on the support 55 to maximize transfer of heat between the
base 130 and the substrate 25. For example, for a substrate 25
having a circular or disk shape, the base 130 comprises a right
cylindrical shape. Typically, the base 130 comprises an
electrically conducting material and is surrounded by an insulating
shield or jacket 150. The base 130 is made out of a metal such as
aluminum, and the jacket 150 is made from an insulating material,
for example, a polymeric or a ceramic material, such as quartz.
Optionally, the base 130 can also be electrically biased by the
voltage supply 95.
[0030] The dielectric 60 of the support 55 isolates the primary
electrode 70 from the substrate 25 and the plasma in the chamber
30. The dielectric 60 can comprise a single layer of insulating
material overlying the base 130 which serves as the primary
electrode 70 (not shown), or a monolith in which the primary
electrode 70 is embedded. Preferably, as shown in FIG. 1, the
dielectric 60 comprises a monolith in which the primary electrode
70 is embedded to substantially entirely isolate the primary
electrode 70 from the plasma. The dielectric 60 is made from a
dielectric material that is resistant to erosion by the gas or
plasma and capable of withstanding high temperatures. The
dielectric 60 comprises an absorption coefficient sufficiently low
to allow the RF voltage applied to the primary electrode 70 to
capacitively couple to the plasma in the chamber 30. Suitable
dielectric materials include, for example, ceramic materials, such
as Al.sub.2O.sub.3, AlN, BN, Si, SiC, Si.sub.3N.sub.4, TiO.sub.2,
ZrO.sub.2, and mixtures and compounds thereof; and polymeric
materials such as polyimide, polyamide, polyetherimide, polyketone,
polyetherketone, polyacrylate, fluoroethylene, or mixtures thereof.
The thickness of the dielectric material overlying the primary
electrode 70 is from about 100 .mu.m to about 1000 .mu.m to permit
an RF voltage applied to the primary electrode 70 to capacitively
couple to the plasma in the chamber 30.
[0031] The dielectric 60 also comprises one or more conduits 160
extending through the dielectric 60, such as for example, a gas
conduit 170 provided to supply heat transfer gas (or second gas) to
an interface between the surface 75 of the dielectric 60 and the
substrate 25. The heat transfer gas, typically helium, promotes
heat transfer between the substrate 25 and the support 55. Other
conduits 160 in the dielectric 60 enable lift-pins 175 to extend
through the support 55 to lift or lower the substrate 25 off the
surface 75 of the dielectric 60 for loading or unloading of the
substrate 25. The conduits 160 have an internal surface 180 and are
typically from about 10 to about 30 mm long--depending on the
thickness of the dielectric 60; and have a polygonal or circular
cross-section having a width or diameter of from about 0.1 to about
3 mm.
[0032] The primary electrode 70 is charged by an RF voltage to
energize the plasma in the chamber 30 during processing of the
substrate 25. The primary electrode 70 comprises an area that is
sufficiently large to uniformly couple RF energy to the gas in the
chamber 30 and across substantially the entire area of the
substrate 25. For example, for a circular substrate 25 having a
diameter of 200 to 300 mm (8 to 12 inches), the primary electrode
70 typically comprises an area of from about 30 to about 70,000
mm.sup.2. In addition, as shown in FIGS. 2a and 2b, the primary
electrode 70 comprises edges 195 around apertures 185 that in turn
extend around the conduits 160 in the dielectric 60. The primary
electrode 70 can comprise a conductor layer, a mesh of conducting
material, or a conducting pattern formed by doping the dielectric
60. Preferably, the primary electrode 70 comprises a mesh or a
plurality of interconnected groups of electrode segments fabricated
from an electrically conducting material. Suitable electrically
conducting materials for the electrode include metal containing
materials, such as for example, aluminum, copper, silver, gold,
molybdenum, tantalum, titanium, or mixtures thereof.
[0033] Optionally, the primary electrode 70 (which is also the
power electrode) is capable of being electrically charged to serve
as an electrostatic chuck to electrostatically hold the substrate
25 to the surface 75 of the dielectric 60. The primary electrode 70
comprises an area below the substrate 25 that is sufficiently large
to electrostatically attract and hold the substrate 25 upon
application of a DC voltage to the electrode 70. The primary
electrode 70 can comprise either a monopolar or bipolar electrodes.
During operation of a monopolar electrode, electrically charged
plasma species in the chamber 30 cause electrical charge to
accumulate in the substrate 25, thereby providing the attractive
electrostatic force that holds the substrate 25 to the dielectric
60. In bipolar mode, the primary electrode 70 comprises first and
second groups of electrode segments (not shown) which are
electrically isolated from one another and are sized and configured
to operate as bipolar electrodes. When bipolar electrode segments
are electrically biased relative to one another, the resultant
electrostatic force between the electrode segments and the
substrate 25 holds the substrate 25 to the dielectric 60.
[0034] In one aspect of the present invention, the thickness of a
portion of the dielectric between an edge 195 of the primary
electrode 70 and the surface 180 of the conduit 160 is made
sufficiently large to reduce the incidence of plasma formation in
the conduit 160 when the primary electrode 70 is charged by an RF
voltage to form a plasma of a gas in the chamber 30. The thickness
of dielectric material between the edge 195 of the primary
electrode 70 and the conduit 160 can be increased either by
reducing the cross-section of the conduits 160 or by forming the
edge 195 of the primary electrode 70 that is further away from the
surface 180 of the conduit 160. The size of the conduits 160
generally depends upon other design parameters, such as dimensions
of the lift-pins 175 or the rate at which heat transfer gas must be
supplied. However, forming the edge 195 of the primary electrode 70
at a predetermined distance away from the surface 180 of the
conduit 160 serves to increase the thickness of dielectric material
between the edge 195 of the primary electrode 70 and the conduit
160 to a thickness that is sufficiently large to reduce plasma
formation in the conduit 160. The desired thickness of the gap
between the electrode edge 195 and the conduit 160 depends on the
RF and DC power levels applied to the primary electrode 70, the
pressure of gas in the conduit 160 and the dimensions of the
conduit 160. If the dielectric thickness between the edge 195 of
the primary electrode 70 and the surface 180 of the conduit 160 is
too small, plasma formation can occur within the conduit 160
thereby damaging the support 55 and overlying substrate 25.
However, when the dielectric thickness is too large, the primary
electrode 70 becomes too small and insufficient RF energy is
coupled to the gas above the conduits 160 resulting in formation of
a weak spot in the plasma at this region of the substrate 25 that
results in poor processing of this region. In addition, if the
primary electrode 70 is charged with a DC voltage (to serve as an
electrostatic chuck) a primary electrode having an excessively
small area results in insufficient electrostatic attraction to hold
the substrate 25 to the surface 75 of the dielectric 60. It has
been discovered that for conduits 160 having the dimensions given
above, a sufficient thickness of dielectric material is from about
2 times to about 200 times the thickness of the portion of the
dielectric 60 that overlies the primary electrode 70. Preferably,
thickness of the dielectric between the edge 195 of the primary
electrode 70 and the surface 180 of the conduit 160 is at least
about 3 mm, and more preferably less than about 10 mm.
[0035] In another aspect of the present invention, the support 55
further comprises a counter or secondary electrode 210 covered by
or embedded in the dielectric 60. The secondary electrode 210 is
adapted to attract an electric field emanating from the edge 195 of
the primary electrode 70 and away from the conduit 160 during
processing of the substrate 25. For example, as shown in FIG. 3,
the secondary electrode 210 comprises a perimeter 225 adjacent to
and extending along the edge 195 of the primary electrode 70 that
circumvents a conduit 160. In operation, the secondary electrode
210 is electrically biased relative to the primary electrode 70 to
reduce the incidence of plasma formation in the conduit 160 during
processing of the substrate 25. For example, when RF power is
applied to the primary electrode 70 the secondary electrode can be
electrically grounded.
[0036] Preferably, the secondary electrode 210 has a surface
comprising an area that is smaller than the area of the primary
electrode 70 to reduce wastage of power from the excessive coupling
of RF and DC electrical energy from the primary electrode 70 to the
secondary electrode 210. Thus, preferably, the secondary electrode
210 comprises a total area that is less than about 5% of the total
area of the primary electrode 70. More preferably, the secondary
electrode 210 comprises a total area of about 1000 to about 2000
mm.sup.2. The total area is the area of an entire surface of the
electrode or a sum of the area of the surfaces of a plurality of
electrode segments.
[0037] In addition, preferably, the secondary electrode 210 is not
in the same plane (non-coplanar) as the primary electrode 70 to
further increase the separation distance or gap between the
secondary electrode 210 and the primary electrode 70. While a
larger gap further reduces leakage of RF or DC energy from the
primary electrode 70; too large a gap can cause the secondary
electrode to be ineffective. Preferably, the secondary electrode
210 is also below the level of the primary electrode 70 to further
reduce the attenuation of energy applied to electrode 210. For
example, as shown in FIG. 4, the secondary electrode 210 can
comprise a thin conducting strip that forms a ring or a collar 220
lying below the level, and about the edge 195, of the primary
electrode 70. Like the primary electrode 70, the secondary
electrode 210 can comprise a conductor layer, a mesh of conducting
material, or a conducting pattern of dopant in the dielectric 60,
and the secondary electrode 210 can be made from the same materials
as the primary electrode 70
[0038] In one version, as shown in FIGS. 5a and 5b, the secondary
electrode 210 is shaped as one or more collars 230 that are
disposed about and adjacent to the conduits 160. Each collar 230
comprises an inner diameter that is larger than the apertures 185
of the primary electrode 70 and an outer diameter that is
sufficiently large to be close to and attract the electric field
emanating out from the edge 195 of the primary electrode 70. This
version reduces plasma formation in the conduits 160 while also
reducing wastage of electrical energy from coupling of RF and DC
energy from the primary electrode 70 to the secondary electrode 210
because of the relatively small size of the collar 230.
[0039] In another version, as shown in FIG. 6, the secondary
electrode 210 comprises a plurality of primary electrode segments
220a, b. The electrode segments 220a, b are positioned a different
distances from the primary electrode 70 and the surface 180 of the
conduit 160. This version is particularly useful for embodiments in
which the support 55 is supported on a base 130 having a dielectric
plug 235 at a lower end of the conduit 160, as shown in FIG. 6. The
dielectric plug 235 is made from a polymeric or ceramic material
and prevents the primary electrode 70 or the substrate 25 from
shorting to the base 130 when a plasma forms in the conduit 160.
The heat transfer gas passes through a narrow gap 245 between the
base 130 and the dielectric plug 235 to enter the conduit 160. As
shown in FIG. 6, a first collar 220a comprising a thin strip of a
conductor lying below and adjacent to the edge 195 of the primary
electrode 70, attracts the electric field emanating from the
primary electrode 70 away from the conduit 160. A second collar
220b, lying over and adjacent to the gap 245 reduces excessive
ingress or penetration of the electric field from the primary
electrode 70 into the gap 245 between the base 130 and the
dielectric plug 235 to reduce the plasma formation therein.
[0040] In another version, shown in FIG. 7, the secondary electrode
210 comprises a cylindrical collar 220c disposed about the conduit,
and lying below and adjacent to the edge 195 of the primary
electrode 70. The relatively large surface area of the collar 220c
parallel to the conduit 160 suppresses RF coupling from the edge
195 of the primary electrode 70 to the gas in the conduit 160 and
substantially eliminates plasma formation in the conduit 160 during
processing of the substrate 25. The collar 220c can be comprise an
inner diameter larger than the aperture 185 of the primary
electrode 70 so that the collar 220c is covered by the primary
electrode 70, as shown in FIG. 7. Alternatively, the collar 220c
can comprise an outer diameter smaller than the aperture 185 as
shown in FIG. 8. The increased separation of the collar from the
primary electrode 70 further reduces leakage of RF or DC current
from the primary electrode 70.
[0041] Optionally, the secondary electrode 210 is electrically
biased relative to the primary electrode 70 by a bias voltage
supply 260. Biasing the secondary electrode 210 enables the
strength with which it attracts the electric field emanating from
the primary electrode 70 to be changed during processing of the
substrate 25. The secondary electrode 210 is electrically biased to
reduce wastage of power caused by coupling of RF and DC energy from
the primary electrode 70 to the secondary electrode 210 while also
reducing the formation of plasma in the conduits 160. This is
particularly desirable for processes in which a relatively low
voltage is applied to the primary electrode 70. In these processes,
the potential for plasma formation in the conduits 160 is low and
the loss of power to a grounded secondary electrode 210 due RF and
DC leakage current can be significant. Thus, biasing the secondary
electrode 210 to a voltage above ground potential reduces the
difference in potential between the secondary electrode 210 and
primary electrode 70, both reduces wastage of power from the
primary electrode 70 and plasma formation in the conduits 160.
Generally, the secondary electrode 210 is biased with a voltage of
from about -1000 to about +1000 volts which can be DC or RF
voltage. The secondary electrode 210 cal also comprise a plurality
of electrode segments that are each at a different distance from
the primary electrode 70 or from the surface 180 of the conduit 160
and that are each biased to a different electrical potential level.
This is particularly useful for a chamber 30 in which different RF
voltages are applied to the primary electrode 70 and the base 130.
The potential applied to each electrode segment is selected to
substantially eliminate plasma formation in the conduit 160 during
processing of the substrate 25 while reducing loss of power due to
RF leakage current.
EXAMPLES
[0042] The following examples show the use of the present invention
in reducing the incidence of plasma formation in a conduit 160 when
the primary electrode 70 is charged by an RF voltage to energize
the plasma ions in the chamber 30 during processing of the
substrate 25. These examples are computer simulations of the
equipotential lines emanating from the primary electrode 70 for
different configurations of the support 55. The computer
simulations of the equipotential lines are illustrated graphically
in FIGS. 9 to 13. The horizontal axis of the graphs represents
distance away from the surface 180 of the conduit 160. The vertical
axis represents the distance from the base 130 of the support 55.
Thus, FIGS. 9 to 13 can be viewed as a partial sectional side view
of the dielectric 60 with the vertical axis representing a section
of the surface 180 of a conduit 160, and the horizontal axis
representing a section of the lower surface of the dielectric 60.
Furthermore, the strength of an electric field (not shown)
extending between any two equipotential lines is directly
proportional to the difference in potential between the
equipotential lines and inversely proportional to the distance
between them. Thus, in FIGS. 9 to 13 the closer together the
equipotential lines, the stronger the electric field at that
point.
[0043] FIG. 9 shows the equipotential lines for a conventional
support 55 comprising a dielectric 60 covering a primary electrode
70 that extends to within about 2.5 mm of the surface 180 of the
conduit 160. In deriving the equipotential lines for FIG. 9, the
substrate 25 was assumed to be at a potential of about 500 volts
DC, the base 130 was grounded, and 1000 volts peak to peak was
applied to the primary electrode 70. The primary electrode 70 can
be thought of as a line source that originates at a point 2.5 mm
from the vertical axis (2.5 mm from the surface 180 of the conduit)
and about 10 mm from the horizontal axis (substantially at the top
of the dielectric 60), and extends parallel to the horizontal axis.
The clustering of equipotential lines near the top of the surface
180 of the conduit 160 (represented by the vertical axis from 7 to
10 mm) suggest a strong electric field that would lead to plasma
formation in the conduit 160.
[0044] FIG. 10 shows the equipotential lines for a support 55
according to the present invention in which the thickness of
dielectric material between the primary electrode 70 and the
surface 180 of the conduit 160 is selected to be about 4 mm. As
before the substrate 25 was assumed to be at a potential of about
500 volts DC, the base 130 was grounded, and 1000 volts peak to
peak were applied to the primary electrode 70. The equipotential
lines intersecting the surface 180 of the conduit 160 (represented
by the vertical axis) are spread out suggesting a weaker electric
field at the surface 180 of the conduit 160, and a reduced
incidence of plasma formation in the conduit 160.
[0045] FIG. 11 shows the equipotential lines for a support 55
comprising a thickness of dielectric material between the primary
electrode 70 and the surface 180 of the conduit 160 of about 6 mm.
As in the preceding examples, the substrate 25 was assumed to be at
a potential of about 500 volts DC, the base 130 was grounded, and
1000 volts peak to peak were applied to the primary electrode 70.
The equipotential lines intersecting the surface 180 of the conduit
160 (represented by the vertical axis) are even more spread out
suggesting a still weaker electric field and a further reduced
incidence of plasma formation in the conduit 160.
[0046] FIG. 12 shows the equipotential lines for a support 55 in
which the thickness of dielectric material between the primary
electrode 70 and the surface 180 of the conduit 160 is selected to
be about 4 mm, and the support 55 further comprises a secondary
electrode 210 below and near the edge 195 of the primary electrode
70 as shown in FIG. 7. In this graph, the substrate 25, the base
130, and the secondary electrode 210 were assumed to be at ground
potential (0 volts), and 700 volts RF were assumed to be applied to
the primary electrode 70. As seen from the equipotential lines
which do not intersect the surface 180 of the conduit 160
(represented by the vertical axis) at all, the grounded secondary
electrode 210 attracts the electric field emanating from the edge
195 of the charged primary electrode 70 away from the conduit 160.
The coupling of RF energy emanating from the edge 195 of the
primary electrode 70, to a gas in the conduit 160 is reduced and
plasma formation in the conduit 160 is substantially
eliminated.
[0047] FIG. 13 shows the equipotential lines for a support 55
having a secondary electrode 210 comprising a plurality of collars
220a, b as shown in FIG. 6. The first collar 220a attracts electric
fields that emanate from the primary electrode 70 and the second
collar 220b prevents the electric fields from penetrating into a
gap 245 between the base 130 and a dielectric plug 235 and forming
a plasma therein. In deriving the equipotential lines for this
graph, the substrate 25 was assumed to be at 500 volts DC and the
base at a potential of about -2500 volts peak to peak. The primary
electrode 70 was assumed to be about 4 mm from the surface 180 of
the conduit 160 and at a potential of about 1000 volts peak to
peak. As shown, fewer than five equipotential lines intersect the
surface 180 of the conduit 160 (represented by the vertical axis),
and these are spread out along the full length of the conduit 160
indicating a greatly reduced electric field and a reduced the
incidence of plasma formation in the conduit 160.
[0048] While the present invention has been described in
considerable detail with reference to certain preferred versions,
many other versions should be apparent to those of ordinary skill
in the art. For example, the secondary electrode 210 can comprise
conducting portions of the surface 180 of the conduits 160
themselves. Therefore, the spirit and scope of the appended claims
should not be limited to the description of the preferred versions
contained herein.
* * * * *