U.S. patent application number 11/278700 was filed with the patent office on 2007-10-11 for method and apparatus for providing uniform gas delivery to a reactor.
Invention is credited to Jeremie J. Dalton, M. Ziaul Karim, Ana R. Londergan.
Application Number | 20070234956 11/278700 |
Document ID | / |
Family ID | 38254883 |
Filed Date | 2007-10-11 |
United States Patent
Application |
20070234956 |
Kind Code |
A1 |
Dalton; Jeremie J. ; et
al. |
October 11, 2007 |
METHOD AND APPARATUS FOR PROVIDING UNIFORM GAS DELIVERY TO A
REACTOR
Abstract
A gas distribution system for a reactor having at least two
distinct gas source orifice arrays displaced from one another along
an axis defined by a gas flow direction from the gas source orifice
arrays towards a work-piece deposition surface such that at least a
lower one of the gas source orifice arrays is located between a
higher one of the gas source orifice arrays and the work-piece
deposition surface. Orifices in the higher one of the gas source
orifice arrays may spaced an average of 0.2-0.8 times a distance
between the higher one of the gas source orifice arrays and the
work-piece deposition surface, while orifices in the lower one of
the gas source orifice arrays may be spaced an average of 0.1-0.4
times a distance between the higher one of the gas source orifice
arrays and the work-piece deposition surface.
Inventors: |
Dalton; Jeremie J.; (San
Jose, CA) ; Karim; M. Ziaul; (San Jose, CA) ;
Londergan; Ana R.; (Santa Clara, CA) |
Correspondence
Address: |
SONNENSCHEIN NATH & ROSENTHAL LLP
P.O. BOX 061080
WACKER DRIVE STATION, SEARS TOWER
CHICAGO
IL
60606-1080
US
|
Family ID: |
38254883 |
Appl. No.: |
11/278700 |
Filed: |
April 5, 2006 |
Current U.S.
Class: |
118/715 |
Current CPC
Class: |
C23C 16/45565 20130101;
C23C 16/45574 20130101; C23C 16/45544 20130101 |
Class at
Publication: |
118/715 |
International
Class: |
C23C 16/00 20060101
C23C016/00 |
Claims
1. A gas distribution system for a reactor, comprising at least two
distinct gas source orifice arrays displaced from one another along
an axis defined by a gas flow direction from the gas source orifice
arrays towards a work-piece deposition surface such that at least a
lower one of the gas source orifice arrays is located between a
higher one of the gas source orifice arrays and the work-piece
deposition surface.
2. The gas distribution system of claim 1, wherein orifices in the
higher one of the gas source orifice arrays are spaced an average
of 0.2-0.8 times a distance between the higher one of the gas
source orifice arrays and the work-piece deposition surface.
3. The gas distribution system of claim 1, wherein orifices in the
lower one of the gas source orifice arrays are spaced an average of
0.1-2 times a distance between the higher one of the gas source
orifice arrays and the work-piece deposition surface.
4. The gas distribution system of claim 1, wherein the higher one
of the gas source orifice arrays comprises a planar source.
5. The gas distribution system of clam 4, wherein the planar source
comprises a showerhead.
6. The gas distribution system of claim 1, wherein the higher one
of the gas source orifice arrays comprises a generally uniform
distribution of orifices across a faceplate.
7. The gas distribution system of claim 6 wherein the lower one of
the gas source orifice arrays comprises one or more conduits
distributed axi-symetrically with respect to a radius of the planar
showerhead.
8. The gas distribution system of claim 1 wherein the lower one of
the gas source orifice arrays comprises one or more conduits
distributed axi-symetrically with respect to the higher one of the
gas source orifice arrays.
9. The gas distribution system as in claim 8, wherein the lower one
of the gas source orifice arrays comprises a number of spoke
conduits leading from an axially centered feed conduit, and each
spoke conduit includes a number of individual orifices spaced an
average of 0.1-2 times a distance between the higher one of the gas
source orifice arrays and the work-piece deposition surface.
10. A method for introducing gases into a reactor, comprising
flowing a purge gas into the reactor from a first gas source
orifice array disposed a first distance from a surface of a
work-piece along an axis defined by gas flow from the first gas
source orifice array to the surface of the work-piece while flowing
a first reactive precursor into the reactor from a second gas
source orifice array separate from the first gas source orifice
array and disposed at a second distance from the surface of a
work-piece along the axis defined by gas flow, said second distance
being less than said first distance.
11. The method of claim 10, further comprising stopping the flow of
the first reactive precursor from the second gas source array.
12. The method of claim 11, further comprising flowing the purge
gas into the reactor from one or more of the first gas source
orifice array and the second gas source orifice array.
13. The method of claim 11, further comprising flowing a second
reactive precursor into the reactor through the first gas source
orifice array while flowing the purge gas into the reactor through
the second gas source orifice array.
14. The method of claim 13, further comprising stopping the flow of
the second reactive precursor from the first gas source array.
15. The method of claim 14, further comprising flowing the purge
gas into the reactor from one or more of the first gas source
orifice array and the second gas source orifice array.
16. The method of claim 15, further comprising evacuating unused
amounts of the second reactive precursor from the reactor.
17. The method of claim 11, further comprising evacuating unused
amounts of the first reactive precursor from the reactor.
18. A method for introducing gases into a reactor, comprising
flowing a carrier gas and a reactive precursor into the reactor
from a first gas source orifice array disposed a first distance
from a surface of a work-piece along an axis defined by gas flow
from the first gas source orifice array to the surface of the
work-piece while flowing a second reactive precursor into the
reactor from a second gas source orifice array separate from the
first gas source orifice array and disposed at a second distance
from the surface of a work-piece along the axis defined by gas
flow, said second distance being less than said first distance.
19. The method of claim 18, wherein the second reactive precursor
is flowed into the reactor in a pulsed fashion via the second gas
source orifice array.
20. The method of claim 18, further comprising stopping the flow of
reactive precursors into the reactor while flowing a purge gas into
the reactor from one or both of the first and second gas source
orifice arrays.
21. A method for introducing gases into a reactor, comprising
flowing a first gas into the reactor from a first gas source
orifice array disposed a first distance from a surface of a
work-piece along an axis defined by gas flow from the first gas
source orifice array to the surface of the work-piece while flowing
a second gas into the reactor from a second gas source orifice
array separate from the first gas source orifice array and disposed
at a second distance from the surface of a work-piece along the
axis defined by gas flow, said second distance being less than said
first distance.
22. The method of claim 21, wherein the first gas comprises a
reactive precursor.
23. The method of claim 21, wherein the first gas comprises a
reactive precursor and a carrier gas.
24. The method of claim 21, wherein the second gas comprises a
reactive precursor.
25. The method of claim 21, wherein the second gas comprises a
reactive precursor and a carrier gas.
26. The method of claim 22, wherein the second gas comprises a
second reactive precursor.
27. The method of claim 22, wherein the second gas comprises a
second reactive precursor and a carrier gas.
28. The method of claim 22, wherein the second gas comprises a
purge gas.
29. The method of claim 24, wherein the first gas comprises a purge
gas.
30. The method of claim 23, wherein the second gas comprises a
second reactive precursor.
31. The method of claim 23, wherein the second gas comprises a
second reactive precursor and a second carrier gas.
32. The method of claim 23, wherein the second gas comprises a
purge gas.
33. The method of claim 29, wherein the second gas comprises a
reactive precursor.
34. The method of claim 29, wherein the second gas comprises a
reactive precursor and a carrier gas.
35. The method of claim 29, wherein the second gas comprises the
purge gas.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a gas distribution system
for an atomic layer deposition or chemical vapor deposition
processing system in which a vapor phase precursor is transported
from an upstream source to a reaction space above a substrate.
BACKGROUND
[0002] The chemical deposition of thin solid films from gaseous
(vapor-phase) chemical precursors onto solid substrates is of great
interest in many areas including semiconductor fabrication,
magnetic data storage, nanotechnology and others. In particular,
atomic layer deposition (ALD) and chemical vapor deposition (CVD)
processes are commonly used to deposit both dielectric and metal
films onto semiconductor substrates. Increasingly, these
applications require that the deposited film meet strict standards
for thickness uniformity across the substrate and repeatability in
such thicknesses over multiple substrates, while at the same time
the process equipment is required to provide high film deposition
rates so as not to present a bottleneck in the overall fabrication
process.
[0003] In order for CVD and ALD equipment to meet such
requirements, the flux of vapor precursors to the substrate must be
tightly controlled and shaped. Often, there can be multiple gaseous
precursors that must react to form the desired film and all must be
delivered to the substrate in a precise and controllable manner. In
some cases, it is advantageous to mix these multiple precursors
together prior to introducing them into the reactor chamber. In
other cases, it is preferable to maintain the precursors isolated
from one another until they come into contact with the substrate so
as to prevent any unwanted premature reactions.
[0004] Generally, uniform precursor flow into the reaction chamber
is attempted by providing a flat plate with many small holes in
between the gas-source and the substrate (a so-called showerhead).
An early description of a device for providing such axial-symmetric
gas flow towards a substrate is provided in U.S. Pat. No. 4,798,165
of deBoer et al. The diffusion plate or showerhead can have
separate zones such that some holes are used for introducing one
precursor and other holes are used for introducing the other
precursor. In this way the precursors are kept separate so that no
mixing occurs prior to the precursors entering the reaction space
adjacent to the substrate.
[0005] One such showerhead is described in U.S. Published Patent
Application 2006-0021703 of Salvador P. Umotoy. In this design, the
showerhead faceplate has a number of gas passageways to provide a
plurality of gases to the process region without commingling of
those gases. A gas distribution manifold assembly is coupled so as
to provide the different gasses to the various gas holes in the
faceplate.
[0006] Another design for maintaining gases in separate passageways
until they exit the distribution plate into the process region is
described in U.S. Pat. No. 5,595,606. This showerhead includes a
multiple block stack that ostensibly maintains two gases in
separate passageways until they exit the distribution plate into
the process region.
[0007] While showerheads of the sort described above purport to
maintain separation of the various gases used in the ALD and CVD
the present inventors have observed that if the relative flow rates
of the different precursors flowing through adjacent holes are not
well designed, recirculation can occur along the showerhead
faceplate between the holes. FIG. 1 illustrates this condition.
Shown in the diagram is a cut away view of a showerhead apparatus
10 having two individual gas manifolds generally indicated at 12
and 14. The upper manifold 12 includes gas passageways 16a and 16b,
which provide means for the gas in manifold 12 to exit via holes
18a and 18b in the faceplate 20 of showerhead 10. Similarly, the
lower manifold 14 includes gas passageways 22a and 22b, which
provide means for the gas in manifold 14 to exit via holes 24a and
24b in faceplate 20.
[0008] As shown, recirculation of the different precursor gases has
been known to occur along the showerhead faceplate 20 between the
holes associated with the different manifolds 12 and 14. This
undesired mixing of the precursors can cause unwanted reactions
therebetween and reduce film uniformity on substrates in proximity
thereto. Furthermore, when multiple zones are present within a
single showerhead the spacing between the outlet holes of different
zones becomes constrained by the number and size of holes required
for flow uniformity.
[0009] Another problem with such showerhead designs is that it is
difficult or impossible to maintain a difference in temperature
between the two precursors because they both flow through the same
solid plate 26 before reaching the faceplate 20. In many cases, it
would be desirable to maintain precursors at different temperatures
until they react at the substrate surface.
[0010] What is needed, therefore, is a gas distribution system that
overcomes these limitations of conventional showerheads.
SUMMARY OF THE INVENTION
[0011] One embodiment of the present invention provides a gas
distribution system for a reactor having at least two distinct gas
source orifice arrays displaced from one another along an axis
defined by a gas flow direction from the gas source orifice arrays
towards a work-piece deposition surface such that at least a lower
one of the gas source orifice arrays is located between an upper
one of the gas source orifice arrays and the work-piece deposition
surface. The precise distance from the upper gas source orifice
array (or the lower gas source orifice array) to the work-piece
deposition surface depends on a number of factors, including the
shape of the individual orifices in each of the arrays and the gas
flow rates for each array. In general, the orifice arrays are
positioned within the reactor such that a relatively uniform
deposition over the work-piece surface can be achieved using the
necessary gases and flow rates for the particular layer to be
deposited. In addition to the distance from the work-piece surface,
the spacing between individual orifices of each array will affect
the nature and quality of the deposited layer. Hence, orifices in
the upper one of the gas source orifice arrays may spaced an
average of 0.2-0.8 times a distance between the higher one of the
gas source orifice arrays and the work-piece deposition surface,
while orifices in the lower one of the gas source orifice arrays
may be spaced an average of 0.1-2 times a distance between the
higher one of the gas source orifice arrays and the work-piece
deposition surface.
[0012] The higher one of the gas source orifice arrays may be a
planar showerhead having a generally uniform distribution of
orifices across its faceplate. The lower one of the gas source
orifice arrays may include one or more conduits distributed
axi-symetrically with respect to a radius of the planar showerhead.
For example, the lower one of the gas source orifice arrays may
include a number of spoke conduits leading from an axially centered
feed conduit, and each spoke conduit including a number of
individual orifices spaced an average of 0.1-2 times a distance
between the higher one of the gas source orifice arrays and the
work-piece deposition surface.
[0013] A further embodiment of the present invention provides for
introducing gases into a reactor by flowing a purge gas from a
first gas source orifice array disposed a first distance from a
surface of a work-piece along an axis defined by gas flow from the
first gas source orifice array to the surface of the work-piece
while flowing a first reactive precursor into the reactor from a
second gas source orifice array separate from the first gas source
orifice array and disposed at a second distance from the surface of
a work-piece along the axis defined by gas flow, said second
distance being between said first distance. At an appropriate time,
the flow of the first reactive precursor from the second gas source
array may be stopped and the purge gas then flowed into the reactor
from one or more of the first gas source orifice array and the
second gas source orifice array. When unused portions of the first
reactive precursor have been evacuated from the reactor, a second
reactive precursor may be flowed into the reactor through the first
gas source orifice array while flowing the purge gas into the
reactor through the second gas source orifice array. Thereafter,
the flow of the second reactive precursor from the first gas source
array may be stopped, and unused portions of the second reactive
precursor evacuated while flowing the purge gas into the reactor
from one or more of the first gas source orifice array and the
second gas source orifice array. This cycle may be repeated as
needed to form a film on a substrate within the reactor.
[0014] Notwithstanding its applicability to ALD processes such as
those described above, the invention is also useful in CVD and/or
pulsed-CVD operations as discussed further below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The present invention is illustrated by way of example, and
not limitation, in the figures of the accompanying drawings, in
which:
[0016] FIG. 1 shows an example of undesired gas recirculation and
mixing which can occur when a conventional showerhead having gas
passageways with exit holes in a single plane is used;
[0017] FIG. 2 shows an example of a showerhead configured in
accordance with an embodiment of the present invention so as to
prevent or reduce such undesired gas recirculation and mixing by
displacing gas passageway exit holes into separate planes displaced
from one another along an axis defined by the gas injection
axis;
[0018] FIG. 3 shows an example of a showerhead configured in
accordance with an embodiment of the present invention in which a
radial spoke gas injection conduit is displaced beneath a planar
gas distribution plate; and
[0019] FIG. 4 shows an example of an ALD reactor having with a gas
distribution system configured in accordance with an embodiment of
the present invention; and
[0020] FIG. 5 illustrates a variation of the ALD system shown in
FIG. 4 in which multiple wafers are processed in a single
rector.
DETAILED DESCRIPTION
[0021] Described herein are gas distribution systems for ALD, CVD
and/or other processing systems in which vapor phase precursors or
other gases (e.g., inert carrier gases) are transported from
upstream sources to a reaction space above a substrate. Unlike such
distribution systems of the past, the present distribution systems
are composed of two or more physically separated gas source
orifices. That is, embodiments of the present invention provide gas
source orifices at different displacements from a surface of a
substrate along an axis of the gas pathway from the orifices to
that surface. Viewed differently, the gas source orifices (which
may be supplied by a common manifold configured to provide gases or
precursors separately to each orifice) are separated from one
another along an axis defining a path for the gasses to travel
between the orifices and the substrate.
[0022] Embodiments of the present invention provide both physical
and thermal separation of reactive precursors until they come into
close proximity to the substrate. This not only avoids undesired
reactions along the faceplate of the showerhead, it also permits
the individual precursors to be delivered at their individual
optimum temperatures. Furthermore, systems configured in accordance
with the present invention provide manufacturers greater
flexibility in designing gas flow manifolds for each precursor,
independent from the geometrical constraints of the other.
[0023] Turning now to FIG. 2, an example of a gas distribution
system 28 configured in accordance with an embodiment of the
present invention is illustrated. Note that although this
illustration depicts a gas distribution system with two manifolds
(or gas source orifice arrays as they are sometimes termed herein),
the present invention is not limited to such systems. Any number of
such manifolds can be used. In some cases, the gas distributions
systems will have multiple gas orifices disposed in a single plane
(such as is the case for the system illustrated in FIG. 1) and in
addition will have other gas orifices disposed in a different plane
(as described below). In other cases, three or more such orifice
arrays separately disposed from one another along an axis of gas
injection may be provided. Thus, the depiction of a system
employing two such arrays displaced from one another is meant only
to illustrate the concepts embodied in the present invention and
should not be viewed as limiting the scope of the invention to such
arrangements.
[0024] FIG. 2 then is a cut away view of a gas distribution system
28 having two individual gas manifolds generally indicated at 30
and 32. The upper manifold 30 includes gas passageways 34a-34d,
which provide means for the gas in manifold 30 to exit via holes
36a-36d in the faceplate 38 of a distribution plate 40. The lower
manifold 32 includes a generally cylindrical gas passageway 40,
which provide means for the gas in manifold 32 to exit via holes
44a-44c.
[0025] Of course, the individual manifolds are not limited to these
illustrated configurations and, in general, any convenient
configurations may be used to achieve desired gas distribution
profiles within a reaction space proximate to a substrate. Thus,
planar, curved, corrugated, cylindrical or other
manifolds/distribution devices may be employed. For example, the
faceplate 38 of upper manifold 30 need not be a flat (or relatively
flat) surface as is shown in the illustration. Instead, faceplate
38 may have a corrugated or even saw tooth profile. Further,
regardless of whether the faceplate 38 is flat or not, it need not
necessarily be planar. Instead, various embodiments of the present
invention may find particular application for a curved (e.g.,
relatively concave or relatively convex) faceplate 38.
[0026] The lower manifold 32 may itself be something other than a
cylindrical gas passageway. For example, the lower manifold may be
a relatively planar diffuser plate. Alternatively, the lower
manifold 32 may be a series of radially projecting cylinders
resembling the spokes of a bicycle wheel (as is shown in later
figures and described further below). In some cases the individual
spoke-like orifice arrays may be of different lengths and/or
diameters and arranged so as to provide a desired gas flow to a
substrate. The spoke-like arrays may be independent of one another
or may be coupled to one another via azimuthally-oriented or
chord-like members and/or gas source orifice arrays.
[0027] In some cases the distance between the lower manifold 32 and
the upper manifold 30 may be adjustable. For example, the lower
manifold 32 may be suspended beneath the upper manifold 30 by one
or more telescoping (e.g., pneumatic or hydraulic) supports which
operate under the control of a controller so as to set the lower
manifold at a desired distance from the faceplate 38 of the upper
manifold 30. Alternatively, the supports or other means of
adjusting the separation distance between the manifolds may be
manually configurable. Different CVD and/or ALD processes may
require such different spacings between the manifolds in order to
achieve desired deposition characteristics on substrates.
[0028] Whether adjustable or not, the optimal distance between the
upper and lower manifolds may be dependent on the characteristics
of the individual orifices present therein. Hence, to accommodate a
wide variety of applications, the present invention encompasses the
use of different types of orifices in either or both of the
manifolds. Some orifices may be substantially cylindrical in
cross-section, while others may be more funnel-like in
cross-section so as to provide a wider dispersal of the gas exiting
the orifice than might otherwise be achieved using orifices having
a cylindrical cross-section. So too may the number of holes in each
individual manifold be adjusted to provide a desired gas
distribution profile at the surface of the work-piece undergoing
processing. Different arrangements of orifice types and numbers in
different radial areas of either or both of the manifolds may
provide for relatively uniform deposition rates across an entire
surface of a substrate. Individual orifices may be circular,
rectangular, square, triangular, etc., in transverse section.
[0029] While these various arrangements of orifices of different
types are not critical to the present invention, the overall goal
of providing a gas delivery system configured to achieve
substantially uniform deposition across an entire substrate surface
while avoiding undesired cross-mixing of precursor gases should not
be overlooked. In the case of a lower manifold having radial,
spoke-like orifice arrays for gas distribution, reduced spacing
between individual orifices would imply having more spokes in the
entire array. This may not necessarily be desirable in that a wider
spacing with fewer individual orifices would provide fewer
opportunities for undesired mixing of precursor gasses along the
arms of the lower gas distribution array and, hence, reduced
overall formation of contaminant particles.
[0030] As shown in FIG. 2, manifold 32 is displaced from manifold
30 along an axis (Z) in the direction of gas injection from the
respective holes of each manifold. Hence, the recirculation of the
different precursor gases from the different manifolds does not
lead to any undesired mixing of the precursors along the faceplate
38 of distribution plate 40. This improves the film deposition
characteristics of systems employing system 28 over those which
make use of conventional showerheads.
[0031] FIG. 3 shows an isometric view of the gas distribution
system 28. The upper manifold is composed of a relatively flat
distribution plate 40 with multiple through-holes 36 in faceplate
38 to allow precursor vapors and purge gases to enter the reactor
(not shown). The lower manifold 32 is configured as an array of
radial tubes 48 joined to a central inlet 50. The tubes 48 have a
series of outlet holes (not shown in detail in this drawing) to
provide for uniform delivery of precursor and purge gases. The
tubes 48 may be organized as one or more conduits distributed
axi-symetrically with respect to a radius of the planar
distribution plate 40.
[0032] FIG. 4 illustrates an example of an ALD reactor 52 having a
gas distribution system configured in accordance with an embodiment
of the present invention. In this cut away view, a wafer 54 is
placed on a susceptor 56 (which may be vertically movable along the
Z axis and may also include a heater) beneath the gas distribution
system 28. The gas distribution system 28 may be part of a lid
assembly for reactor 52 or may be separate therefrom. As indicated
above, the gas distribution system includes an upper manifold 30,
which is configured to receive precursor A from an upstream source,
and a lower manifold 32, which is configured to receive precursor B
from a separate upstream source. Each of the manifold may also be
configured to receive purge gasses. Manifold 30 distributes
precursor A towards substrate 54 through holes (not shown in this
view) in the faceplate 38, while manifold 32 distributes precursor
B towards substrate 54 through holes (also not shown in this view)
in radial arms 48. The radial arms are fed via central inlet 50.
Manifold 32 is displaced below the faceplate 38 of manifold 30
along the axis of gas injection towards the substrate 54 (the Z
axis) by a distance "d".
[0033] FIG. 5 illustrates a variation of the above-described system
in which multiple wafers or other substrates 60 are accommodated in
a single reactor 52. The wafers 60 may be supported on a linear
array 56'. Alternatively, the wafers may be placed in a radial
array that resembles a carousel. Accordingly, the wafers 60 could
be aligned along radial directions with respect to the center of a
circular supporting element. A multi-wafer reactor of this type may
be used where backside depositions can be tolerated (or otherwise
compensated for) and may improve overall throughput. Similarly,
reactors such as reactor 52 may be configured for use in
stand-alone tools or in multi-single wafer tools or in cluster
tools.
[0034] Importantly, the lower manifold 48 need not have a radial
spoke configuration as depicted in the illustration. In some cases
the lower manifold may be a point source (i.e., a gas orifice
having a substantially circular or other cross-section).
Alternatively, the lower manifold 48 could be a planar (or
relatively planar) source, a source having a concave cross-section,
or a radial spoke configuration with spokes of varying lengths.
Further, the lower manifold 48 may be relatively smaller or larger
than as depicted in the illustration. That is, the lower manifold
48 may have a diameter equal to or greater than the substrate 54.
or, the lower manifold may have a diameter smaller than that of the
substrate, as shown.
[0035] Moreover, precursor B need not necessarily be fed to the
lower manifold 32 via a single, central supply line. Instead, some
configurations may have precursor B being fed to the orifice array
through a lateral line or other, non central axial-symmetric feed
line or lines. The details of such gas feed lines from an external
gas supply source are not critical to the present invention.
[0036] In one embodiment of the present invention, the faceplate 38
of manifold 30 is located a distance "L" from the surface of
substrate 54 on which deposition is to occur. In practice, "L" will
be an average distance of an intended plane defined by the
faceplate 38 from the surface of the substrate 54 and individual
distances of any point on the faceplate 38 will reside at a
distance L.+-..delta.1 from said surface, owing to nonuniformities
in the faceplate surface and the surface of the substrate 54.
Preferably, the holes in faceplate 38 through which precursor A
gases will be introduced to reactor 52 will spaced an average of
0.2-0.8 times L.+-..delta.1 from one another. In further
embodiments, the holes in manifold 32 may be spaced an average of
0.1-2 times L.+-..delta.1 from one another. Note that this latter
spacing may be achieved through selected positioning of the various
radial arms 48 of manifold 32.
[0037] Further, the distance from the lower manifold 32 to the
surface of the substrate 54 will be some fraction of L. In various
embodiments of the invention this distance may be 0.3-0.9 * L, and
in one embodiment that was reduced to practice was 0.7L. Typically,
L will be approximately one inch.
[0038] During a typical ALD process in which the present gas
distribution assembly would be used, manifold 30 will be flowing
purge gas while manifold 32 is flowing reactive precursor B. In the
next step of the process both manifolds 30 and 32 will flow purge
gas to assist in removing any unreacted precursor from the reactor
52. Unused precursors and purge gases are exhausted from reactor 52
via a pumping arrangement (not shown). Next, precursor A will be
introduced through manifold 30 and purge gas will flow through
manifold 32. Finally, both manifolds 30 and 32 will flow purge gas
to assist in removing any unreacted precursor. The flows of
precursor and purge gas may be alternated in this fashion
throughout the deposition process to allow the substrate 54 to be
sequentially exposed to each of the precursors without allowing the
precursors to mix in the gas phase.
[0039] The above-described process allows for uniform delivery of
precursor vapor by introducing one of the reactant species through
a flat plate with a plurality of through-holes while the second
reactant species is introduced through a set of conduits radiating
outward from a centrally located inlet. The conduits are situated
such that they are between the flat plate and the substrate. This
provides delivery of both reactants while maintaining thermal and
physical isolation between the chemicals.
[0040] In some ALD processes, one of the ALD half-reactions will be
soft saturating while the other is not. In such cases it may be
desirable to introduce the precursor associated with the soft
saturating half reaction through the upper manifold. For example,
the precursor associated with the soft saturating reaction may
require more uniform distribution, as may be achieved through
introduction via the upper, relatively planar gas orifice array. In
contrast, the precursor associated with the strongly saturating
half-reaction in the ALD process may be relatively insensitive to
distribution via a nonuniform gas orifice array such as the lower
manifold. This may not always be the case, however, inasmuch as
relative gas flow rates must also be taken into consideration.
[0041] In addition to ALD processes, the present invention may be
used in connection with CVD and/or pulsed-CVD processes. In a
typical CVD process both manifold 30 and manifold 32 may be flowing
purge gases and/or reactive precursors (potentially with respective
carrier gasses). When a desired deposition has been achieved, the
flow of reactive precursors will be stopped and either or both
manifolds 30 and 32 may flow purge gas to assist in removing any
remaining precursors from the reactor 52.
[0042] In a pulsed-CVD process a first precursor and carrier gas
may be introduced continually through manifold 30 and the second
precursor introduced in a pulsed fashion through the lower manifold
32. Preferably, the precursor introduced via the lower manifold
will be the one which has a dominant surface reaction during the
CVD. As before, once the desired deposition has been achieved, the
unused precursors and purge gases are exhausted from reactor 52
while flowing purge gas through one or both of the manifolds.
[0043] In further embodiments, the two manifolds may be operated so
as to variously flow reactive precursors, precursors and carrier
gases, and/or purge gas at various times in an ALD, CVD or other
process so as to achieve a desired deposition on a substrate within
the reactor. For example, while a precursor is introduced via the
upper manifold (with or without a carrier gas), the lower manifold
may be used to introduce a second precursor (with or without its
own carrier gas) or purge gas and vice-versa.
[0044] Thus, a gas distribution system composed of distinct,
physically separated source orifices to supply precursor vapors and
inert gases to a substrate has been described. The distinct gas
sources are oriented such that one orifice is located between the
substrate and the other orifice. This prevents gas recirculation
that is often observed with conventional showerheads, when the
precursor vapors and inert gases are injected through adjacent
orifices, and prevents premature reactions that are often observed
when the precursors and purge gases are introduced through a single
orifice. Stated differently, in contrast to conventional
showerheads gas distribution systems configured in accordance with
the present invention do not provide a gas recirculation zone
between the outlet orifices of the separate gas manifolds. This
improves purging and can minimize gas-phase mixing and turbulence,
both of which can lead to unwanted film deposition or particle
formation
[0045] It should be apparent from the preceding discussion that the
use of separate gas source orifices that are not constrained to a
single flat-plate allows much more freedom in designing the size
and shape of each precursor manifold. When both precursor manifolds
are constrained to have their outlet orifices in the same
horizontal plane as in a conventional showerhead, the designer may
not be able to achieve optimal flow uniformity for both precursors.
At a minimum, the designer may have to resort to complex manifold
and gas flow passages to achieve uniform flow. However, when
separating the precursor manifolds into distinct orifices that are
not in the same plane, in accordance with the present invention, it
is much easier to obtain gas flow uniformity with simple gas flow
passages. Of course, although the present invention was discussed
with reference to certain illustrated embodiments, these examples
should not be used to limit the broader scope of the invention as
set forth in the following claims.
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