U.S. patent application number 09/773409 was filed with the patent office on 2001-06-28 for magnetically enhanced inductively coupled plasma reactor with magnetically confined plasma.
This patent application is currently assigned to Applied Materials, Inc.. Invention is credited to Loewenhardt, Peter K., Salzman, Philip M., Yin, Gerald Z..
Application Number | 20010004920 09/773409 |
Document ID | / |
Family ID | 24364615 |
Filed Date | 2001-06-28 |
United States Patent
Application |
20010004920 |
Kind Code |
A1 |
Loewenhardt, Peter K. ; et
al. |
June 28, 2001 |
Magnetically enhanced inductively coupled plasma reactor with
magnetically confined plasma
Abstract
The invention is embodied in a plasma reactor including a
chamber enclosure having a process gas inlet and including a
ceiling, a sidewall and a workpiece support pedestal capable of
supporting a workpiece at a plasma processing location facing the
ceiling, the workpiece processing location and ceiling defining a
process region therebetween, the pedestal being spaced from said
sidewall to define a pumping annulus therebetween having inner and
outer walls, to permit process gas to be evacuated therethrough
from the process region. The invention further includes a pair of
opposing plasma confinement magnetic poles arranged adjacent the
annulus within one of the inner and outer walls of the annulus, the
opposing magnetic poles being axially displaced from one another
the opposite poles being oriented to provide maximum magnetic flux
in a direction across the annulus and a magnetic flux at the
processing location less than the magnetic flux across the
annulus.
Inventors: |
Loewenhardt, Peter K.;
(Pleasanton, CA) ; Yin, Gerald Z.; (San Jose,
CA) ; Salzman, Philip M.; (San Jose, CA) |
Correspondence
Address: |
PATENT COUNSEL
APPLIED MATERIALS, INC.
Legal Affairs Department
P.O. BOX 450A
Santa Clara
CA
95052
US
|
Assignee: |
Applied Materials, Inc.
|
Family ID: |
24364615 |
Appl. No.: |
09/773409 |
Filed: |
January 31, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09773409 |
Jan 31, 2001 |
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09521799 |
Mar 9, 2000 |
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09521799 |
Mar 9, 2000 |
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09263001 |
Mar 5, 1999 |
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09263001 |
Mar 5, 1999 |
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08766119 |
Dec 16, 1996 |
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6030486 |
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08766119 |
Dec 16, 1996 |
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08590998 |
Jan 24, 1996 |
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Current U.S.
Class: |
156/345.29 ;
118/723I; 156/345.49 |
Current CPC
Class: |
H01J 37/3266 20130101;
H01J 37/321 20130101; H01J 37/32834 20130101 |
Class at
Publication: |
156/345 ;
118/723.00I |
International
Class: |
H01L 021/3065 |
Claims
What is claimed is:
1. A plasma reactor comprising: a chamber enclosure having a
process gas inlet and including a ceiling, a sidewall and a
workpiece support pedestal capable of supporting a workpiece at a
plasma processing location facing the ceiling, said workpiece
processing location and ceiling defining a process region
therebetween, said pedestal being spaced from said sidewall to
define a pumping annulus therebetween having inner and outer walls,
to permit process gas to be evacuated therethrough from the process
region; a pair of opposing plasma confinement magnetic poles
arranged adjacent said annulus within one of said inner and outer
walls of said annulus, the opposing magnetic poles being axially
displaced from one another said opposite poles being oriented to
provide maximum magnetic flux in a direction across said annulus
and a magnetic flux at said processing location less than the
magnetic flux across said annulus.
2. The reactor of claim 1 further comprising a connector of
magnetically permeable material within said one wall connecting
said opposing wall.
3. The reactor of claim 1 wherein said pair of poles comprise a
horseshoe magnet.
4. The reactor of claim 2 wherein said magnetic poles are ring
shaped and are concentric with said annulus.
5. The reactor of claim 4 wherein said connector is ring shaped and
concentric with said annulus.
6. The reactor of claim 1 wherein said magnetic poles are within
said inner wall.
7. The reactor of claim 1 wherein said magnetic poles are within
said outer wall.
8. The reactor of claim 3, in which said horseshoe magnet is
ring-shaped and concentric with said annulus.
9. The reactor of claim 8, in which said horseshoe magnet is within
one of said inner and outer walls.
10. The reactor of claim 11 in which the opposite poles are
connected by a magnetically permeable connector.
11. The reactor of claim 1 which further includes a horseshoe
magnet arrangement having a pair of legs respectively terminating
in said opposite poles, with at least one ring magnet comprising
one leg of the horseshoe arrangement, and with the remainder of the
arrangement being of magnetically permeable material.
12. A plasma reactor comprising: a chamber having a process gas
inlet and enclosing a plasma process region; a workpiece support
pedestal within said chamber and capable of supporting a workpiece
at a processing location open to said plasma process region, said
support pedestal and chamber defining an annulus therebetween
having opposed walls to permit gas to be evacuated therethrough
from said process region; a ring-shaped horseshoe magnet positioned
adjacent and about said annulus within one of said inner and outer
walls of said annulus, the horseshoe magnet being oriented to
direct its maximum magnetic flux across said annulus and a reduced
magnetic flux elsewhere.
13. The reactor of claim 1 wherein said horseshoe magnet is within
a radially inner one of said opposed walls.
14. The reactor of claim 1 wherein said horseshoe magnet is within
a radially outer one of said opposed walls.
Description
CROSS REFERENCE
[0001] This is a continuation of U.S. application Ser. No.
09/521,799, filed Mar. 9, 2000, which is a continuation of U.S.
application Ser. No. 09/263,001, filed Mar. 5, 1999, which is a
continuation-in-part of U.S. application Ser. No. 08/766,119, filed
Dec. 16, 1996, which is a continuation of now-abandoned U.S.
application Ser. No. 08/590,998, filed Jan. 24, 1996.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] The invention is related to plasma reactors for processing
semiconductor wafers, and in particular confinement of the
processing plasma in the reactor within a limited processing
zone.
[0004] 2. Background Art
[0005] Plasma reactors, particularly radio frequency (RF) plasma
reactors of the type employed in semiconductor wafer plasma
processing in the manufacturing of microelectronic integrated
circuits, confine a plasma over a semiconductor wafer in the
processing chamber by walls defining a processing chamber. Such an
approach for plasma confinement has several inherent problems where
employed in plasma reactors for processing semiconductor
wafers.
[0006] First, the walls confining the plasma are subject to attack
from ions in the plasma, typically, for example, by ion
bombardment. Such attack can consume the material in the walls or
introduce incompatible material from the chamber walls into the
plasma process carried out on the wafer, thereby contaminating the
process. Such incompatible material may be either the material of
the chamber wall itself or may be material (e.g., polymer)
previously deposited on the chamber walls during plasma processing,
which can flake off or be sputtered off. As one example, if the
chamber walls are aluminum and the plasma process to be performed
is plasma etching of silicon dioxide, then the material of the
chamber wall itself, if sputtered into the plasma, is incompatible
with the process and can destroy the integrity of the process.
[0007] Second, it is necessary to provide certain openings in the
chamber walls and, unfortunately, plasma tends to leak or flow from
the chamber through these openings. Such leakage can reduce plasma
density near the openings, thereby upsetting the plasma process
carried out on the wafer. Also, such leakage can permit the plasma
to attack surfaces outside of the chamber interior. As one example
of an opening through which plasma can leak from the chamber, a
wafer slit valve is conventionally provided in the chamber side
wall for inserting the wafer into the chamber and withdrawing the
wafer from the chamber. The slit valve must be unobstructed to
permit efficient wafer ingress and egress. As another example, a
pumping annulus is typically provided, the pumping annulus being an
annular volume below the wafer pedestal coupled to a vacuum pump
for maintaining a desired chamber pressure. The chamber is coupled
to the pumping annulus through a gap between the wafer pedestal
periphery and the chamber side wall. The flow of plasma into the
pumping annulus permits the plasma to attack the interior surfaces
or walls of the pumping annulus. This flow must be unobstructed in
order for the vacuum pump to efficiently control the chamber
pressure, and therefore the pedestal-to-side wall gap must be free
of obstructions.
[0008] It is an object of the invention to confine the plasma
within the chamber without relying entirely on the chamber walls
and in fact to confine the plasma in areas where the chamber walls
to not confine the plasma. It is a related object of the invention
to prevent plasma from leaking or flowing through openings
necessarily provided the chamber walls. It is an auxiliary object
to so prevent such plasma leakage without perturbing the plasma
processing of the semiconductor wafer.
[0009] It is a general object of the invention to shield selected
surfaces of the reactor chamber interior from the plasma.
[0010] It is a specific object of one embodiment of the invention
to shield the interior surface of the reactor pumping annulus from
the plasma by preventing plasma from flowing through the gap
between the wafer pedestal and the chamber side wall without
obstructing free flow of charge-neutral gas through the gap.
[0011] It is a specific object of another embodiment of the
invention to prevent plasma from flowing through the wafer slit
valve in the chamber side wall without obstructing the ingress and
egress of the wafer through the wafer slit valve.
SUMMARY OF THE DISCLOSURE
[0012] The invention is embodied in a plasma reactor including a
chamber enclosure having a process gas inlet and including a
ceiling, a sidewall and a workpiece support pedestal capable of
supporting a workpiece at a plasma processing location facing the
ceiling, the workpiece processing location and ceiling defining a
process region therebetween, the pedestal being spaced from said
sidewall to define a pumping annulus therebetween having inner and
outer walls, to permit process gas to be evacuated therethrough
from the process region. The invention further includes a pair of
opposing plasma confinement magnetic poles arranged adjacent the
annulus within one of the inner and outer walls of the annulus, the
opposing magnetic poles being axially displaced from one another
the opposite poles being oriented to provide maximum magnetic flux
in a direction across the annulus and a magnetic flux at the
processing location less than the magnetic flux across the
annulus.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a cut-away side view of a plasma reactor in
accordance with a first embodiment of the invention employing open
magnetic circuits.
[0014] FIG. 2 is an enlarged view of the magnetic confinement
apparatus near the pedestal-to-side wall gap.
[0015] FIG. 3 is an enlarged view of the magnetic confinement
apparatus near the wafer slit valve.
[0016] FIGS. 4A and 4B correspond to a side view of a plasma
reactor in accordance with a preferred embodiment of the invention
employing closed magnetic circuits having pairs of opposed
magnets.
[0017] FIG. 5 is a perspective view of a pair of opposing ring
magnets juxtaposed across the pedestal-to-side wall gap.
[0018] FIG. 6 is a perspective view of a pair of opposing magnets
juxtaposed across the wafer slit valve.
[0019] FIG. 7 is a cut-away side view of a plasma reactor in which
the closed magnetic circuit is a single magnet whose opposing poles
are juxtaposed across the pedestal-to-side wall gap and which are
joined by a core extending across the pumping annulus.
[0020] FIG. 8 is a top view of the single magnet of FIG. 7 and
showing the gas flow holes through the core joining the opposite
poles of the magnet.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] Conventional Reactor Elements:
[0022] Referring to FIG. 1, an RF plasma reactor for processing a
semiconductor wafer has a vacuum chamber 10 enclosed by a
cylindrical side wall 12, a ceiling 14 and a floor 16. A wafer
pedestal 18 supports a semiconductor wafer 20 which is to be
processed. A plasma precursor gas is injected into the chamber 10
through a gas injector 22 from a gas supply 24. Plasma source power
is coupled into the chamber 10 in any one of several ways. For
example, the reactor may be a "diode" configuration, in which case
RF power is applied across a ceiling electrode 26 and the wafer
pedestal 18. This is accomplished by connecting the pedestal 18 and
the ceiling electrode 26 to either one of two RF power sources 28,
30. Alternatively, a cylindrical side coil 32 wound around the
chamber side wall 12 is connected to an RF power source 34.
Alternatively to the foregoing, or in addition thereto, a top coil
36 is connected to an RF power supply. As is conventional, the
wafer pedestal 18 may have its own independently controllable RF
power supply 28 so that ion bombardment energy at the wafer surface
can be controlled independently of plasma density, determined by
the RF power applied to the coil 32 or the coil 36.
[0023] A vacuum pump 40 is coupled to the chamber 10 through a
passage 42 in the floor 16. The annular space between the periphery
of the wafer pedestal 18 and the floor 16 forms a pumping annulus
44 through which the vacuum pump 40 evacuates gas from the chamber
10 to maintain a desired processing pressure in the chamber 10. The
pumping annulus 44 is coupled to the interior of the chamber 10
through an annular gap 46 between the periphery of the wafer
pedestal 18 and the chamber side wall 14. In order for the pump 40
to perform efficiently, the gap 46 is preferably free of
obstructions.
[0024] A conventional slit valve opening 50 of the type well-known
in the art having a long thin opening in the chamber side wall 14
provides ingress and egress for a semiconductor wafer 52 to be
placed upon and withdrawn from the wafer pedestal 18.
[0025] The walls 12, 14 confining the plasma within the chamber 10
are subject to attack from plasma ions and charged radicals,
typically, for example, by ion bombardment. Such attack can consume
the material in the walls 12, 14 or introduce incompatible material
from the chamber walls 12, 14 into the plasma process carried out
on the wafer 52, thereby contaminating the process. Such
incompatible material may be either the material of the chamber
wall itself or may be material (e.g., polymer) previously deposited
on the chamber walls during plasma processing, which can flake off
or be sputtered off. Plasma reaching the chamber walls can cause
polymer deposition thereon.
[0026] The openings from the interior portion of the chamber 10,
including the pedestal-to-side wall gap 46 and the slit valve
opening 50, permit the plasma to leak or flow from the chamber 10.
Such leakage can reduce plasma density near the openings 46, 50,
thereby upsetting the plasma process carried out on the wafer 52.
Also, such leakage can permit the plasma to attack surfaces outside
of the chamber interior. The flow of plasma into the pumping
annulus 44 through the gap 46 permits the plasma to attack the
interior surfaces or walls of the pumping annulus 44. Thus, the
designer must typically take into account not only the materials
forming the chamber ceiling 12 and side wall 14, but in addition
must also take into account the materials forming the pumping
annulus, including the lower portion 56 of the side wall 14, the
floor 16 and the bottom peripheral surface 58 of the wafer pedestal
18, which complicates the design. Such a loss of plasma from the
chamber 10 also reduces plasma density or requires more plasma
source power to maintain a desired plasma density over the wafer
52.
[0027] Magnetic Confinement:
[0028] In order to prevent plasma from flowing from the chamber 10
into the pumping annulus, a magnetic field perpendicular to the
plane of the gap 46 and perpendicular to the direction of gas flow
through the gap 46 is provided across the gap 46. This is
preferably accomplished by providing an opposing pair of magnetic
poles 60, 62 juxtaposed in facing relationship across the gap 46.
In the embodiment according to FIG. 2, the magnetic pole 60 is the
north pole of a magnet 64 located at the periphery of the wafer
pedestal 18 while the magnetic pole 62 is the south pole of a
magnet 66 next to the inner surface of the side wall 14. The
embodiment of FIG. 2 may be regarded as an open magnetic circuit
because the returning magnetic field lines of flux 68 in FIG. 2
radiate outwardly as shown in the drawing.
[0029] In order to prevent plasma from flowing from the chamber 10
through the slit valve opening 50, a magnetic field perpendicular
to the plane of the slit valve opening 50 and perpendicular to the
direction of gas flow through the slit valve opening 50 is provided
across the slit valve opening 50. This is preferably accomplished
by providing an opposing pair of magnetic poles 70, 72 juxtaposed
in facing relationship across the slit valve opening 50. In the
embodiment according to FIG. 3, the magnetic pole 70 is the north
pole of a magnet 74 extending across the bottom edge of the slit
valve opening 50 while the magnetic pole 72 is the south pole of a
magnet 76 extending along the top edge of the slit valve opening
50. The embodiment of FIG. 3 may also be regarded as an open
magnetic circuit because the returning magnetic field lines of flux
78 in FIG. 3 radiate outwardly as shown in the drawing.
[0030] One potential problem with the returning lines of magnetic
flux 68 (FIG. 2) and 78 (FIG. 3) is that some returning flux lines
extend near the wafer 52 and may therefore distort or perturb
plasma processing of the wafer 52. In order to minimize or
eliminate such a problem, a closed magnetic circuit (one in which
returning magnetic lines of flux do not extend into the chamber) is
employed to provide the opposing magnetic pole pairs 60, 62 and 70,
72. For example, in the embodiment of FIGS. 4 and 5, the opposing
magnetic poles 60, 62 across the gap 44 are each a pole of a
respective horseshoe ring magnet 80, 82 concentric with the wafer
pedestal 18. The horseshoe ring magnet 80 has the north pole 60 and
a south pole 81 while the horseshoe ring magnet has the south pole
62 and a north pole 83. The poles 60, 81 of the inner horseshoe
ring magnet 80 are annuli connected at their inner radii by a
magnetic cylindrical core annulus 85. Similarly, the poles 62, 83
of the outer horseshoe ring magnet 82 are annuli connected at their
outer radii by a magnetic cylindrical core annulus 86. The magnetic
circuit consisting of the inner and outer horseshoe ring magnets
80, 82 is a closed circuit because the lines of magnetic flux
between the opposing pole pairs 60, 62 and 81, 83 extend straight
between the poles and, generally, do not curve outwardly, at least
not to the extent of the outwardly curving returning lines of flux
68, 78 of FIGS. 2 and 3.
[0031] In the embodiment of FIGS. 4A, 4B and 6, the opposing
magnetic poles 70, 72 across the slit valve opening 50 are each a
pole of a respective long horseshoe magnet 90, 92 extending along
the length of the slit valve opening 50. The long horseshoe magnet
90 extends along the top boundary of the slit valve opening 50
while the other horseshoe magnet extends along bottom edge of the
slit valve opening 50.
[0032] The advantage of the closed magnetic circuit embodiment of
FIG. 4 is that the magnetic field confining the plasma does not
tend to interfere with plasma processing on the wafer surface.
[0033] In the embodiment of FIGS. 7 and 8, the lower annuli 81, 83
of the two horseshoe ring magnets 80, 82 are joined together as a
single annulus by a magnetic core annulus 96, so that the horseshoe
ring magnets 80, 82 constitute a single horseshoe ring magnet 94
having a north pole 60 and a south pole 62. The core annulus 96
extends across the pumping annulus 44 and can be protected by a
protective coating 98 such as silicon nitride. In order to allow
gas to pass through the pumping annulus 44, the core annulus 96 has
plural holes 100 extending therethrough.
[0034] One advantage of the invention is that plasma ions are
excluded from the pumping annulus 44. This is advantageous because
the pumping annulus interior surfaces can be formed of any
convenient material without regard to its susceptibility to attack
by plasma ions or compatibility of its sputter by-products with the
plasma process carried out on the wafer. This also eliminates
reduction in plasma density due to loss of plasma ions through the
pumping annulus. Another advantage is that gas flow through the
pedestal-to-side wall gap 46 is not obstructed even though plasma
is confined to the interior chamber 10 over the wafer. Furthermore,
by so confining the plasma to a smaller volume (i.e., in the
portion of the chamber 10 directly overlying the wafer 52), the
plasma density over the wafer 52 is enhanced. A further advantage
is that stopping plasma ions from exiting through the slit valve
opening 50 eliminates loss of plasma density over portions of the
wafer 52 adjacent the slit valve opening 50.
[0035] In one example, each of the magnetic pole pair 60, 62 has a
strength of 20 Gauss for a distance across the gap 46 of 5 cm,
while each of the magnetic pole pair 70, 72 has a strength of 20
Gauss for a width of the slit valve opening 50 of 2 cm.
[0036] While the invention has been described with reference to
preferred embodiments in which the plasma confining magnets are
protected from attack from plasma ions and processing gases by
being at least partially encapsulated in the chamber walls or
within the wafer pedestal or within a protective layer, in some
embodiments (as for example, the embodiment of FIG. 6) the magnets
may be protected by being located entirely outside of the chamber
walls. Alternatively, if the reactor designer is willing to permit
some plasma interaction with the magnets, magnets may be located
inside the chamber in direct contact with the plasma, although this
would not be preferred.
[0037] While the invention has been described in detail by specific
reference to preferred embodiments, it is understood that
variations and modifications thereof may be made without departing
from the true spirit and scope of the invention.
* * * * *