U.S. patent application number 13/595351 was filed with the patent office on 2013-04-25 for electron beam plasma source with profiled chamber wall for uniform plasma generation.
This patent application is currently assigned to Applied Materials, Inc.. The applicant listed for this patent is Kallol Bera, Kenneth S. Collins, Leonid Dorf, Shahid Rauf. Invention is credited to Kallol Bera, Kenneth S. Collins, Leonid Dorf, Shahid Rauf.
Application Number | 20130098553 13/595351 |
Document ID | / |
Family ID | 48135004 |
Filed Date | 2013-04-25 |
United States Patent
Application |
20130098553 |
Kind Code |
A1 |
Bera; Kallol ; et
al. |
April 25, 2013 |
ELECTRON BEAM PLASMA SOURCE WITH PROFILED CHAMBER WALL FOR UNIFORM
PLASMA GENERATION
Abstract
A plasma reactor that generates plasma in a workplace processing
chamber by an electron beam, has an electron beam source chamber
with a wall opposite to the electron beam propagation direction,
the wall being profiled to compensate for a non-uniformity in
electron beam density distribution.
Inventors: |
Bera; Kallol; (San Jose,
CA) ; Collins; Kenneth S.; (San Jose, CA) ;
Rauf; Shahid; (Pleasanton, CA) ; Dorf; Leonid;
(San Jose, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Bera; Kallol
Collins; Kenneth S.
Rauf; Shahid
Dorf; Leonid |
San Jose
San Jose
Pleasanton
San Jose |
CA
CA
CA
CA |
US
US
US
US |
|
|
Assignee: |
Applied Materials, Inc.
Santa Clara
CA
|
Family ID: |
48135004 |
Appl. No.: |
13/595351 |
Filed: |
August 27, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61549355 |
Oct 20, 2011 |
|
|
|
Current U.S.
Class: |
156/345.4 |
Current CPC
Class: |
H01J 37/3233 20130101;
H01J 2237/06366 20130101 |
Class at
Publication: |
156/345.4 |
International
Class: |
C23F 1/08 20060101
C23F001/08 |
Claims
1. A plasma reactor for processing a workpiece, comprising: a
workpiece processing chamber having a processing chamber comprising
a chamber ceiling and a chamber side wall and an electron beam
opening in said chamber side wall, a workpiece support pedestal in
said processing chamber having a workpiece support surface facing
said chamber ceiling and defining a workpiece processing region
between said workpiece support surface and said chamber ceiling,
said electron beam opening facing said workpiece processing region;
an electron beam, source chamber comprising a source enclosure,
said source enclosure having an electron beam emission window that
is open to said electron beam opening of said workpiece processing
chamber, and defining an electron beam propagation path along a
longitudinal direction extending through said electron beam
emission window and through said electron beam opening and into
said workpiece processing region, said source enclosure further
comprising a back wall displaced from said electron beam emission
window by a gap along said longitudinal direction, said electron
beam emission window extending generally along a direction
transverse to said longitudinal direction; an electron beam
extraction grid, across said electron beam emission window, an
extraction voltage source coupled to said electron beam extraction
grid, and the said electron beam source chamber; and said back wall
having a profile corresponding to a distribution of said gap along
said transverse direction.
2. The plasma reactor of claim 1 wherein said distribution of said
gap corresponds to a distribution in electron beam density along
said transverse direction.
3. The plasma reactor of claim 1 wherein said distribution of said
gap along said transverse direction corresponds to a measured
distribution in electron beam density distribution along said
transverse direction.
4. The plasma reactor of claim 1 wherein said distribution of said
gap along said transverse direction is center-low, wherein said gap
has a minimum value at a center location of said back wall along
said transverse direction.
5. The plasma reactor of claim 4 wherein said distribution of said
gap along said transverse direction of said electron beam source
chamber compensates for a measured distribution of plasma density
along said transverse direction that is center-high.
6. The plasma reactor of claim 1 wherein said distribution of said
gap along said transverse direction is center-high, wherein said
gap has a maximum value at a center location of said back wall
along said transverse direction.
7. The plasma reactor of claim 6 wherein said distribution of said
gap along said transverse direction of said electron beam source
chamber compensates for a measured distribution of plasma, density
distribution along said transverse direction that is
center-low.
8. The plasma reactor of claim 1 wherein said, distribution of said
gap along said transverse direction has a variance of least 1%.
9. The plasma reactor of claim 1 wherein said distribution of said
gap along said transverse direction has a variance of at least
5%.
10. The plasma reactor of claim 1 wherein back wall is configurable
for changing said profile.
11. The plasma reactor of claim 1 wherein said back wall comprises
a flexible member capable of deforming between different
curvatures, and an actuator coupled to said flexible member.
12. The plasma reactor of claim 11 wherein said different
curvatures comprise a curvature corresponding to a concave profile
or a curvature corresponding to a convex profile.
13. The plasma reactor of claim 1 wherein said source enclosure
further comprises a ceiling, a floor facing said ceiling, plural
elongate slots in one of said floor and ceiling, said slots spaced
apart from one another and at least some of said slots extending in
different directions relative to said transverse and longitudinal
directions, and plural slats removably inserted into selected ones
of said slots to form respective barriers extending from said floor
to said ceiling and through the selected, slots, said back wall
comprising the slats inserted through said slots.
14. The plasma reactor of claim 13 wherein said selected slots
comprises a set of said plural slots corresponding to one of plural
profiles.
15. The plasma reactor of claim 14 wherein said plural profiles
comprise a convex profile or a concave profile.
16. The plasma reactor of claim 14 wherein said plural profile
corresponds to a measured distribution in electron beam density
distribution along said transverse direction.
17. The plasma reactor of claim 11 wherein said different
curvatures comprise a curvature corresponding to a measured
distribution in electron beam density distribution along said
transverse direction.
18. The plasma reactor of claim 1 further comprising: an electron
beam acceleration grid or slot separated by a dielectric from the
said electron beam extraction grid, an acceleration voltage source
coupled to said electron beam acceleration grid or slot, and the
said extraction grid.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 61/549,355, filed Oct. 20, 2011 entitled
ELECTRON BEAM PLASMA SOURCE WITH PROFILED CHAMBER WALL FOR UNIFORM
PLASMA GENERATION, by Kalloi Bera, et al.
BACKGROUND
[0002] A plasma reactor for processing a workplace can employ an
electron beam as a plasma source. Such a plasma reactor can exhibit
non-uniform distribution of processing results (e.g., distribution
of etch rate across the surface of a workpiece) doe to non-uniform
density distribution of the electron beam. Such non-uniformities
can be distributed in a direction transverse to the beam
propagation direction.
SUMMARY
[0003] A plasma reactor for processing a workpiece, includes a
workpiece processing chamber having a processing chamber including
a chamber ceiling and a chamber side wall and an electron beam
opening in the chamber side wall, a workpiece support pedestal in
the processing chamber having a workpiece support surface facing
the chamber ceiling and defining a workpiece processing region
between the workpiece support surface and the chamber ceiling, the
electron beam opening facing the workpiece processing region. The
plasma reactor further includes an electron beam source chamber
including a source enclosure, the source enclosure having an
electron beam emission window that is open to the electron beam
opening of the workpiece processing chamber, and defining an
electron beam propagation path along a longitudinal direction
extending through the electron beam emission window and through the
electron beam opening and into the workpiece processing region, the
source enclosure further including a back wall displaced from the
electron beam emission window by a gap along the longitudinal
direction, the electron beam emission window extending generally
along a direction transverse to the longitudinal direction. An
electron beam extraction grid extends across the electron beam
emission window. An extraction voltage source is coupled to the
electron beam extraction grid, and a supply of plasma source power
is coupled to the electron beam source chamber. The back wall has a
profile corresponding to a variance in the gap along the transverse
direction. In one embodiment, the profile is selected to be
complementary to a variance in electron beam density along the
transverse direction. In a related embodiment, the variance in the
gap corresponds to a measured variance in electron beam density
distribution along the transverse direction. The profile may be
actively configurable. For example, the back wall may consist of
plural slats that are removably inserted into the source enclosure
through a. particular selection of various slots. Each profile
corresponds to a different selection of the slots. As another
example, the back wall may be a flexible sheet that can be deformed
to different curvatures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] So that the manner in which the exemplary embodiments of the
present invention are attained and can be understood in detail, a
more particular description of the invention, briefly summarized
above, may be had by reference to the embodiments thereof which are
illustrated in the appended drawings. It is to be appreciated that
certain well known processes are not discussed herein in order to
not obscure the invention.
[0005] FIG. 1A is a side view of a plasma reactor having an
electron beam generator as a plasma source, and having a beam dump
that is profiled electrically or structurally.
[0006] FIG. 1B is an enlarged view of a portion of FIG. 1A.
[0007] FIG. 1C is a top view of the plasma reactor of FIG. 1A, in
which a plasma source chamber wall has a convex profile.
[0008] FIG. 1D is a top view of the plasma reactor of FIG. 1A, in
which a plasma source chamber wall has a concave profile.
[0009] FIGS. 2A and 2B depict different aspects of an embodiment in
which profiling is implemented in a stepped configuration.
[0010] FIG. 3 depicts an embodiment which is transformable between
different profiles, using insertable partitions.
[0011] FIGS. 3A, 3B and 3C depict different configurations of the
embodiment of FIG. 3.
[0012] FIG. 3D is a detailed view of a portion of the embodiment of
FIG. 3.
[0013] FIG. 4 depicts an embodiment which is transformable between
different profiles, using a flexible chamber wall.
[0014] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures. It is contemplated that elements
and features of one embodiment may be beneficially incorporated in
other embodiments without further recitation. It is to be noted,
however, that the appended drawings illustrate only exemplary
embodiments of this invention and are therefore not to be
considered limiting of its scope, for the invention may admit to
other equally effective embodiments.
DETAILED DESCRIPTION
[0015] Referring to FIGS. 1A, 1B and 1C, a plasma reactor has an
electron beam plasma source. The reactor includes a process chamber
100 enclosed by a cylindrical side wall 102, a floor 104 and a
ceiling 106. A workpiece support pedestal 108 supports a workplace
110, such as a semiconductor wafer, the pedestal 108 being movable
in the axial (e.g., vertical) direction. A gas distribution plate
112 is integrated with or mounted on the ceiling 106, and receives
process gas from a process gas supply 114. A vacuum pump 116
evacuates the chamber through the floor 104. A process region 118
is defined between the workpiece 110 and the gas distribution plate
112. Within the process region 118, the process gas is ionized to
produce a plasma for processing of the workpiece 110.
[0016] The plasma is generated in process region 118 by an electron
beam from an electron beam source 120. The electron beam source 120
includes a plasma generation chamber 122 outside of the process
chamber 100 and having a conductive enclosure 124. The conductive
enclosure 124 includes side wails 124b, a ceiling 124c, a floor
124d and a back wall 124e. The conductive enclosure 124 has a gas
inlet or neck 125. An electron beam source gas supply 127 is
coupled to the gas inlet 125. The conductive enclosure 124 has an
opening 124a facing the process region 118 through an opening 102a
in the sidewall 102 of the process chamber 100.
[0017] The electron beam source 120 includes an extraction grid 126
between the opening 124a and the plasma generation chamber 122, and
an acceleration grid 128 between the extraction grid 126 and the
process region 118, best seen in the enlarged view of FIG. 1B. The
extraction grid 126 and the acceleration grid 128 may be formed as
separate conductive meshes, for example. The extraction grid 126
and the acceleration grid 128 are mounted with insulators 130, 132,
respectively, so as to be electrically insulated from one another
and from the conductive enclosure 124. However, the acceleration
grid 128 is in electrical contact with the side wall 102 of the
chamber 100. The openings 124a and 102a and the extraction and
acceleration grids 126, 128 can be mutually congruent, generally,
and define a thin wide beam flow path for an electron beam into the
processing region 118. The width of the flow path is about the
diameter of the workpiece 110 (e.g., 100-500 mm) while the height
of the flow path is less than approximately two inches.
[0018] The electron beam source 120 further includes a pair of
electromagnets 134-1 and 134-2 adjacent opposite sides of the
chamber 100, the electromagnet 134-1 surrounding the electron beam
source 120. The electromagnets 134-1 and 134-2 produce a magnetic
field parallel to the direction of the electron beam along an
electron beam path. The electron beam flows across the processing
region 118 over the workpiece 110, and is absorbed on the opposite
side of the processing region 118 by a beam dump 136. The beam dump
136 is a conductive body having a shape adapted to capture the wide
thin electron beam.
[0019] A plasma D.C. discharge voltage supply 140 is coupled to the
conductive cathode enclosure 124, and provides extraction voltage
between cathode 124 and extraction grid 126. One terminal of an
electron beam acceleration voltage supply 142 is connected to the
extraction grid 126 and the other terminal to the acceleration grid
128 through the ground potential of the sidewall 102 of the process
chamber 100. A coil current supply 146 is coupled to the
electromagnets 134-1 and 134-2. Plasma is generated within the
chamber 122 of the electron beam source 120 by a D.C. gas discharge
produced by power from the voltage supply 140, to produce a plasma
throughout the chamber 122. This D.C. gas discharge is the plasma
source of the electron beam source 120. Electrons are extracted
from the plasma in the chamber 122 through the extraction grid 126,
and accelerated through the acceleration grid 128 due to a voltage
difference between the acceleration grid and the extraction grid to
produce an electron beam that flows into the processing chamber
100.
[0020] The distribution of electron density across the width of the
beam (along the X-axis or direction transverse to beam travel)
affects the uniformity of plasma density distribution in the
processing region 118. The electron beam may have a measured
non-uniform distribution, in the absence of features that correct
such non-uniformities, which features are described below. Such
non-uniformity may be measured from etch depth distribution
measured on a workpiece or wafer processing in the reactor chamber
described above. Such measured non-uniformity may be caused by
electron drift due to the interaction of the bias electric field
with the magnetic field, divergence of electron beam due to self
electric field and/or electron collision with neutral gas in the
process chamber. Such non-uniformity may also be caused by fringing
of an electric field at the edge of the electron beam. The
distribution of electron density across the width of the beam
(across the X-axis or direction transverse to beam travel) is
liable to exhibit non-uniformities due to the foregoing causes.
Such non-uniformities may correspond to a variance in plasma
electron density distribution in the electron beam across the width
of the electron beam in a range of 1% to 20%, for example. Such a
variance may be measured in that it may be inferred from the
measurements of etch depth distribution in a test wafer referred to
above.
[0021] The back wall 124e of the conductive enclosure 124 is
profiled along the transverse direction (X-axis). The profiling is
chosen to compensate for a measured non-uniformity along the
transverse direction in electron density distribution of the
electron beam. For example, in the embodiment of FIG. 1C, the back
wall 124e is profiled in an internally convex shape, in which the
back wall 124e curves inwardly in the volume of the chamber 122
near the center and curves outwardly toward the side wails 124b.
The back wall 124e and the opening 124a define a gap G parallel to
the beam direction or Y-axis, the gap G having a variance along the
transverse direction or X-axis in accordance with the profile of
the back wall 124e.
[0022] In the embodiment of FIG. 1D, the back wall 124e is profiled
in an internally concave shape, in which the back wall 124e curves
outwardly relative to the volume of the chamber 122 near the center
and curves inwardly toward the side walls 124b.
[0023] It is believed that such profiling changes the effective
cathode area along the transverse direction, which changes the
distribution of ion current to the cathode (i.e., the conductive
envelope 124) along the transverse direction. This creates a
corresponding change in distribution along the transverse direction
of electron current through the extraction grid 126. For example, a
constriction in volume reduces plasma electron density. Thus, in
the embodiment of FIG. 1C, the convex shape of the back wall 124e
tends to render plasma electron distribution along the transverse
direction center low and edge high, and is therefore suitable when
the uncorrected distribution is center high. In the embodiment of
FIG. 1D, the concave shape of the back wall 124e tends to render
plasma electron distribution along the transverse direction center
high and edge low, and is therefore suitable when the uncorrected
distribution is center low. The variance of the gap G is chosen to
match the variance in plasma electron density distribution along
the transverse direction. For example, if the plasma electron
distribution has a center-high non-uniformity or variance of a
particular value (e.g., 5%), then the convex shape of FIG. 1C is
employed, and the profile of the back wall 124e in such a case is
configured so that the gap G has a variance of a similar value
(e.g., 5%), Similarly, if the plasma electron distribution has a
center-low non-uniformity or variance of a particular value (e.g.,
5%), then the concave shape of FIG. 1D is employed, and the profile
of the back wall 124e in such a case is configured so that the gap
G has a variance of a similar value (e.g., 5%). The electron
density distribution may have a variance in a range from 1% to 20%,
for example, and the variance in the gap G may be chosen within
this range.
[0024] FIGS. 2A and 28 depict embodiments in which the
[0025] profiling of FIGS. 1C and 1D, respectively, is implemented
in a stepped manner.
[0026] FIG. 3 depicts an embodiment that may be transformed between
different stepped configurations, including the stepped
configurations of FIGS. 2A and 2B. In FIG. 3A, elongate slots 200
in the ceiling 124c extend along respective directions. Individual
slats or flat partitions 210 may be inserted into respective slots
200. The individual partitions 210 are slidable into and out from
individual slots 200 until their bottom edges contact the floor
124d, and may therefore be individually inserted or removed from
the enclosure 124. Individual partitions 210 are inserted into
selected ones of the slots 200 to form a contiguous conductive
barrier consisting of the inserted partitions 210. This barrier may
conform with either the convex or concave stepped profile of FIG.
2A or 2B, for example, or any other suitable profile. For each
stepped configuration, some of the slots 200 have no partitions
inserted into them and are therefore empty. Each slot 200 that is
empty may be sealed with a slot cover 230 depicted in FIG. 3D.
[0027] FIGS. 3A through 3C depict different configurations of the
partitions 210 of FIG. 3. The partitions 210 are indicated by
cross-hatching, to distinguish them from empty slots 200. FIGS. 3A
and 3B depict configurations corresponding to concave and convex
profiles, respectively. FIG. 3C depicts a configuration having an
almost fiat profile. FIG. 3D is an enlarged view illustrating
certain details in accordance with related embodiments.
Specifically, FIG. 3D illustrates how an individual slot cover 230
may be used to close unused slots 200. A number of slot covers 230
may be furnished to accommodate many possible configurations. In
FIG. 3D, a shallow trough 124f is provided in the surface of the
floor 124d, each trough 124f being in registration with a
corresponding slot 200 in the ceiling 124c, and functioning to
guide and hold in place the bottom edge of each partition 210
inserted into a slot 200. In order to provide a sealed enclosure,
the top of each partition 210 and each slot cover 230 is provided
with a lip 225 as depicted in FIG. 3D, and a deformable ring seal
is provided under the lip.
[0028] FIG. 4 depicts an embodiment in which the back wall 124e is
a flexible metal sheet fastened at its side edges 124e-1, 124e-2 to
the side walls 124b. Top and bottom edges of the back wall 124e are
free to slide against the ceiling 124c and floor 124a. Thus, the
back wall 124e is free to flex between the convex curved shape of
FIG. 1C and the concave curved shape of FIG. 1D. An actuator 250 is
linked by an arm 255 to the back wall 124e, and thereby flexes the
back wall 124e to the convex or concave profiles, under user
control.
[0029] While the main plasma source in the electron beam source 120
is a D.C. gas discharge produced by the voltage supply 140, any
other suitable plasma, source may be employed instead as the main
plasma source. For example, the main plasma source of the electron
beam source 120 may be a toroidal RF plasma source, a capacitively
coupled RF plasma source, or an inductively coupled RF plasma
source.
[0030] While the foregoing is directed to embodiments of the
present invention, other and further embodiments of the invention
may be devised without departing from the basic scope thereof, and
the scope thereof is determined by the claims that follow.
* * * * *