U.S. patent application number 10/946849 was filed with the patent office on 2005-06-09 for thermal processing system with cross flow injection system with rotatable injectors.
Invention is credited to Du Bois, Dale R., Herring, Robert B., Porter, Cole.
Application Number | 20050121145 10/946849 |
Document ID | / |
Family ID | 34396311 |
Filed Date | 2005-06-09 |
United States Patent
Application |
20050121145 |
Kind Code |
A1 |
Du Bois, Dale R. ; et
al. |
June 9, 2005 |
Thermal processing system with cross flow injection system with
rotatable injectors
Abstract
An apparatus is provided for thermally processing substrates
held in a carrier. The apparatus includes an injection system which
provides for selectable injection of gases to the process chamber.
The injection system comprises one or more elongated injection
tubes having a plurality of injection ports or orifices distributed
in the tubes for directing flow of reactant and other gases across
the surface of each substrate. The elongated injection tubes are
rotatable about an axis in 360 degrees.
Inventors: |
Du Bois, Dale R.; (Los
Gatos, CA) ; Porter, Cole; (San Jose, CA) ;
Herring, Robert B.; (San Jose, CA) |
Correspondence
Address: |
DORSEY & WHITNEY LLP
INTELLECTUAL PROPERTY DEPARTMENT
4 EMBARCADERO CENTER
SUITE 3400
SAN FRANCISCO
CA
94111
US
|
Family ID: |
34396311 |
Appl. No.: |
10/946849 |
Filed: |
September 21, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60506354 |
Sep 25, 2003 |
|
|
|
Current U.S.
Class: |
156/345.33 |
Current CPC
Class: |
C23C 16/45578 20130101;
C23C 16/4584 20130101; C23C 16/45508 20130101 |
Class at
Publication: |
156/345.33 |
International
Class: |
C23F 001/00 |
Claims
What is claimed is:
1. A thermal process apparatus suitable for processing a plurality
of substrates supported in a carrier, the apparatus comprising a
cross-flow injection system for directing flow of reactant and
other gases across the surface of each substrate, said cross-flow
injection system comprising one or more elongated tubes each of
which is rotatable about an axis and provided with a plurality of
injection ports.
2. The apparatus of claim 1 wherein said plurality of injection
ports are formed in a line and longitudinally distributed in the
one or more elongated tubes.
3. The apparatus of claim 1 wherein said one or more elongated
tubes are rotatable about an axis in 360 degrees.
4. The apparatus of claim 1 further comprising a cross-flow liner
enclosing the carrier, wherein said cross-flow injection system is
disposed between the liner and the carrier and rotatable in 360
degrees.
5. The apparatus of claim 4 wherein the one or more elongated tubes
are rotated to orient the plurality of injection ports to face the
liner such that gases exiting the injection ports impinge the liner
prior to crossing the surface of each substrate.
6. The apparatus of claim 4 wherein the one or more elongated tubes
are rotated to orient the plurality of injection ports to face each
other such that gases exiting the injection ports impinge each
other prior to crossing the substrate.
7. The apparatus of claim 4 wherein the one or more elongated tubes
are rotated to orient the plurality of injection ports to face the
center of each substrate.
8. The apparatus of claim 4 wherein the cross-flow liner comprises
a cylinder having a close end and an open end, said cylinder is
provided with a longitudinal bulging section, and said cross-flow
injection system is accommodated in the bulging section.
9. The apparatus of claim 8 wherein said cross-flow injection
system comprises one or more elongated tubes accommodated in the
bulging section.
10. The apparatus of claim 9 wherein the open end is provided with
two openings for receiving the elongated tubes.
11. The apparatus of claim 10 wherein the openings are provided
with notches for orienting the injection ports to a predetermined
direction.
12. An apparatus for thermally processing a plurality of substrates
held in a carrier, the apparatus comprising: a process chamber
providing a process region for the substrates; a cross-flow liner
enclosing the substrates held in the carrier; and a cross-flow
injection system disposed between the carrier and the cross-flow
liner to direct flow of one or more gases across the surface of
each substrate, said cross-flow injection system comprising one or
more elongated tubes each of which is rotatable about an axis and
provided with a plurality of injection ports.
13. The apparatus of claim 12 wherein said process chamber is sized
to process 1 to 100 substrate.
14. The apparatus of claim 12 wherein said cross-flow injection
system comprises a first and a second elongated injection tube each
of which is provided with a plurality of injection ports formed in
a line and longitudinally distributed in the tube, wherein each
elongated injection tube is rotatable about an axis in 360
degrees.
15. The apparatus of claim 14 wherein said cross-flow liner
comprises a cylinder having a close end and an open end, said
cylinder is provided with a longitudinal bulging section to
accommodate said first and second elongated injection tubes.
16. The apparatus of claim 15 wherein said close end is provided
with openings to receive the first and second elongated injection
tubes.
17. The apparatus of claim 16 wherein said openings are provided
with notches and each injection tube is provided with an index pin
to be locked in a notch so that the injection ports in the first
and second elongated injection tubes are oriented to a
predetermined direction.
18. The apparatus of claim 12 wherein the cross-flow liner is
patterned and sized so that the liner is conformal to the carrier
and has an inner diameter that is about 104 to 110 percent of a
diameter of the substrates.
19. The apparatus of claim 18 wherein the cross-flow liner is
provided with a plurality of slots cooperating with the plurality
of the injection ports for exhausting gases.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of and priority to U.S.
Provisional Patent Application No. 60/506,354 filed Sep. 25, 2003,
the disclosure of which is hereby incorporated by reference in its
entirety, and is related to PCT application Serial No.
PCT/US03/21575 entitled Thermal Processing System and Configurable
Vertical Chamber, which claims priority to U.S. Provisional patent
application Ser. Nos. 60/396,536 and 60/428,526, the disclosures of
all of which are hereby incorporated by reference in their
entirety.
TECHNICAL FIELD
[0002] The present invention relates generally to systems and
methods for heat-treating objects, such as substrates. More
specifically, the present invention relates to an apparatus and
method for heat treating, annealing, and depositing layers of
material on or removing layers of material from a semiconductor
wafer or substrate.
BACKGROUND
[0003] Thermal processing apparatuses are commonly used in the
manufacture of integrated circuits (ICs) or semiconductor devices
from semiconductor substrates or wafers. Thermal processing of
semiconductor wafers include, for example, heat treating,
annealing, diffusion or driving of dopant material, deposition or
growth of layers of material, and etching or removal of material
from the substrate. These processes often call for the wafer to be
heated to a temperature as high as 1300.degree. C. and as low as
300.degree. C. before and during the process, and that one or more
fluids, such as a process gas or reactant, be delivered to the
wafer. Moreover, these processes typically require that the wafer
be maintained at a uniform temperature throughout the process,
despite variations in the temperature of the process gas or the
rate at which it is introduced into the process chamber.
[0004] A conventional thermal processing apparatus typically
consists of a voluminous process chamber positioned in or
surrounded by a furnace. Substrates to be thermally processed are
sealed in the process chamber, which is then heated by the furnace
to a desired temperature at which the processing is performed. For
many processes, such as Chemical Vapor Deposition (CVD), the sealed
process chamber is first evacuated, and once the process chamber
has reached the desired temperature a reactive or process gases are
introduced to form or deposit reactant species on the
substrates.
[0005] In the past, thermal processing apparatus typically and in
particular vertical thermal processing apparatuses, required guard
heaters disposed adjacent to sidewalls of the process chamber above
and below the process zone in which product wafers were processed.
This arrangement is undesirable since it entails a larger chamber
volume that must be pumped down, filled with process gas or vapor,
and backfilled or purged, resulting in increased processing time.
Moreover, this configuration takes up a tremendous amount of space
and power due to a poor view factor of the wafers from the
heaters.
[0006] Other problems with conventional thermal processing
apparatuses include the considerable time required both before
processing to ramp up the temperature of the process chamber and
the wafer to be treated, and the time required after processing to
ramp down the temperature. Furthermore, additional time is often
required to ensure the temperature of the process chamber has
stabilized uniformly at the desired temperature before processing
can begin. While the actual time required for processing of the
wafers may be half hour or less, pre- and post-processing times
typically take 1 to 3 hours or longer. Thus, the time required to
quickly ramp up and/or down the temperature of the process chamber
to a uniform temperature significantly limits the throughput of the
conventional thermal processing apparatus.
[0007] A fundamental reason for the relatively long ramp up and
ramp down times is the thermal mass of the process chamber and/or
furnace in conventional thermal processing apparatuses, which must
be heated or cooled prior to effectively heating or cooling the
wafer.
[0008] A common approach to minimizing or offsetting this
limitation on throughput of conventional thermal processing
apparatus has been to increase the number of wafers capable of
being processed in a single cycle or run. Simultaneous processing
of a large number of wafers helps to maximize the effective
throughput of the apparatus by reducing the effective processing
time on a per wafer basis. However, this approach also increases
the magnitude of the risk should something go wrong during
processing. That is a larger number of wafers could be destroyed or
damaged by a single failure, for example, if there was an equipment
or process failure during a single processing cycle. This is
particularly a concern with larger wafer sizes and more complex
integrated circuits where a single wafer could be valued at from
$1,000 to $10,000 depending on the stage of processing.
[0009] Another problem with this solution is that increasing the
size of the process chamber to accommodate a larger number of
wafers increases the thermal mass effects of the process chamber,
thereby reducing the rate at which the wafer can be heated or
cooled. Moreover, larger process chambers processing larger batches
of wafers leads to or compounds a first-in-last-out syndrome in
which the first wafers loaded into the chamber are also the last
wafers removed, resulting in these wafers being exposed to elevated
temperatures for longer periods and reducing uniformity across the
batch of wafers.
[0010] Another problem with the above approach is that systems and
apparatuses used for many of the processes before and after thermal
processing are not amenable to simultaneous processing of large
numbers of wafers. Thus, thermal processing of large batches or
large numbers wafers, while increasing the throughput of the
thermal processing apparatus, can do little to improve the overall
throughput of the semiconductor fabrication facility and may
actually reduce it by requiring wafers to accumulate ahead of the
thermal processing apparatus or causing wafers to bottleneck at
other systems and apparatuses downstream therefrom.
[0011] An alternative to the conventional thermal processing
apparatus described above, are rapid thermal processing (RTP)
systems that have been developed for rapidly thermal processing of
wafers. Conventional RTP systems generally use high intensity lamps
to selectively heat a single wafer or small number of wafers within
a small, transparent, usually quartz, process chamber. RTP systems
minimize or eliminate the thermal mass effects of the process
chamber, and since the lamps have very low thermal mass, the wafer
can be heated and cooled rapidly by instantly turning the lamps on
or off.
[0012] Unfortunately, conventional RTP systems have significant
shortcomings including the placement of the lamps, which in the
past were arranged in zones or banks each consisting of a number of
lamps adjacent to sidewalls of the process chamber. This
configuration is problematic because it takes up a tremendous
amount of space and power in order to be effective due to their
poor view factor, all of which are at a premium in the latest
generation of semiconductor processing equipment.
[0013] Another problem with conventional RTP systems is their
inability to provide uniform temperature distribution across
multiple wafers within a single batch of wafers and even across a
single wafer. There are several reasons for this non-uniform
temperature distribution including (i) a poor view factor of one or
more of the wafers by one or more of the lamps, and (ii) variation
in output power from the lamps.
[0014] Moreover, failure or variation in the output of a single
lamp can adversely affect the temperature distribution across the
wafer. Because of this in most lamp-based systems, the wafer or
wafers are rotated to ensure that the temperature non-uniformity
due to the variation in lamp output is not transferred to the wafer
during processing. However, the moving parts required to rotate the
wafer, particularly the rotating feedthrough into the process
chamber, adds to the cost and complexity of the system, and reduces
the overall reliability thereof.
[0015] Yet another troublesome area for RTP systems is in
maintaining uniform temperature distribution across the outer edges
and the center of the wafer. Most conventional RTP systems have no
adequate means to adjust for this type of temperature
non-uniformity. As a result, transient temperature fluctuations
occur across the surface of the wafer that can cause the formation
of slip dislocations in the wafer at high temperatures, unless a
black body susceptor is used that is larger in diameter than the
wafer.
[0016] Conventional lamp-based RTP systems have other drawbacks.
For example, there are no adequate means for providing uniform
power distribution and temperature uniformity during transient
periods, such as when the lamps are powered on and off, unless
phase angle control is used which produces electrical noise.
Repeatability of performance is also usually a drawback of
lamp-based systems, since each lamp tends to perform differently as
it ages. Replacing lamps can also be costly and time consuming,
especially when one considers that a given lamp system may have
upwards of 180 lamps. The power requirement may also be costly,
since the lamps may have a peak power consumption of about 250
kWatts.
[0017] Accordingly, there is a need for an apparatus and method for
quickly and uniformly heating a batch of one or more substrates to
a desired temperature across the surface of each substrate in the
batch of during thermal processing.
SUMMARY OF THE INVENTION
[0018] The present invention provides a solution to these and other
problems, and offers other advantages over the prior art.
[0019] The present invention provides an apparatus and method for
isothermally heating work pieces, such as semiconductor substrates
or wafers, for performing processes such as annealing, diffusion or
driving of dopant material, deposition or growth of layers of
material, and etching or removal of material from the wafer.
[0020] A thermal processing apparatus is provided for processing
substrates held in a carrier at high or elevated temperatures. The
apparatus includes a process chamber having a top wall, a side wall
and a bottom wall, and a heating source having a number of heating
elements proximal to the top wall, the side wall and the bottom
wall of the process chamber to provide an isothermal environment in
a process zone in which the carrier is positioned to thermally
process the substrates. According to one aspect, the dimensions of
the process chamber are selected to enclose a volume substantially
no larger than a volume necessary to accommodate the carrier, and
the process zone extends substantially throughout the process
chamber. Preferably, the process chamber has dimensions selected to
enclose a volume substantially no larger than 125% of that
necessary to accommodate the carrier. More preferably, the
apparatus further includes a pumping system to evacuate the process
chamber prior to processing pressure and a purge system to backfill
the process chamber after processing is complete, and the
dimensions of the process chamber are selected to provide both a
rapid evacuation and a rapid backfilling of the process
chamber.
[0021] According to another aspect of the invention, the bottom
wall of the process chamber includes a movable pedestal having at
least one heating element therein, and the movable pedestal is
adapted to be lowered and raised to enable the carrier with the
substrates to be inserted into and removed from the process
chamber. In one embodiment, the apparatus further includes a
removable thermal shield adapted to be inserted between heating
element in the pedestal and the substrates held the carrier. The
thermal shield is adapted to reflect thermal energy from the
heating element in the pedestal back to the pedestal, and to shield
the substrates on the carrier from thermal energy from the heating
element in the pedestal. In one version of this embodiment, the
apparatus further includes a shutter adapted to be moved into place
above the carrier to isolate the process chamber when the pedestal
is in a lowered position. Where the apparatus includes a pumping
system to evacuate the process chamber, and the shutter can be
adapted to seal with the process chamber, thereby enabling the
pumping system to evacuate the process chamber when the pedestal is
in the lowered position.
[0022] In yet another embodiment, the apparatus further includes a
magnetically coupled repositioning system that repositions the
carrier during thermal processing of the substrates. Preferably,
the mechanical energy used to reposition the carrier is
magnetically coupled through the pedestal to the carrier without
use of a movable feedthrough into the process chamber, and
substantially without moving the heating element in the pedestal.
More preferably, the magnetically coupled repositioning system is a
magnetically coupled rotation system that rotates the carrier
within the process zone during thermal processing of the
substrates.
[0023] According to yet another aspect of the invention, the
apparatus further includes a liner separating the carrier from the
top wall and the side wall of the process chamber, and a
distributive or cross-flow injection system to direct flow of a
fluid across surfaces of each of the substrates held in the
carrier. The cross-flow injection system generally includes a
cross-flow injector having a number of injection ports positioned
relative to substrates held in the carrier, and through which the
fluid is introduced on one side of the number of substrates. A
number of exhaust ports in the liner positioned relative to the
substrates held in the carrier cause the fluid to flow across the
surfaces of the substrates. Fluids introduced by the cross-flow
injection system can include process gas or vapor, and inert purge
gases or vapor used for purging or backfilling the chamber or for
cooling the substrates therein.
[0024] In another aspect, the apparatus of the present invention
includes an injection system which provides for selectable
injection of gases to the process chamber. In general, the
injection system of the present invention comprises one or more
elongated injection tubes having a plurality of injection ports or
orifices distributed in the tubes for directing flow of reactant
and other gases across the surface of each substrate. The elongated
injection tubes are rotatable about an axis in 360 degrees.
[0025] In another embodiment, the apparatus of the present
invention comprises a process chamber providing a process region
for a plurality of substrates held in a carrier, a cross-flow liner
enclosing the carrier, and a cross-flow injection system disposed
between the carrier and the cross-flow liner to direct flow of one
or more gases across the surface of each substrate. The cross-flow
injection system comprising a plurality of injection ports
rotatable about an axis.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] These and various other features and advantages of the
present invention will be apparent upon reading of the following
detailed description in conjunction with the accompanying drawings
and the appended claims provided below, where:
[0027] FIG. 1 is a cross-sectional view of a thermal processing
apparatus having a pedestal heater for providing an isothermal
control volume according to an embodiment of the present invention,
employing conventional up-flow configuration;
[0028] FIG. 2 is a perspective view of an alternative embodiment a
base-plate useful in the thermal processing apparatus shown in FIG.
1;
[0029] FIG. 3 is a cross-sectional view of a portion of a thermal
processing apparatus having a pedestal heater and a thermal shield
according to an embodiment of the present invention;
[0030] FIG. 4 is a diagrammatic illustration of the pedestal heater
and thermal shield of FIG. 3 according to an embodiment of the
present invention;
[0031] FIG. 5 is a diagrammatic illustration of an embodiment of
the thermal shield having a top layer of material with a high
absorptivity and a lower layer of material with a high reflectivity
according to present invention;
[0032] FIG. 6 is a diagrammatic illustration of another embodiment
of the thermal shield having a cooling channel according to present
invention;
[0033] FIG. 7 is a perspective view of an embodiment of a thermal
shield and an actuator according to present invention;
[0034] FIG. 8 is a cross-sectional view of a portion of a thermal
processing apparatus having a shutter according to an embodiment of
the present invention;
[0035] FIG. 9 is a cross-sectional view of a process chamber having
a pedestal heater and a magnetically coupled wafer rotation system
according to an embodiment of the present invention;
[0036] FIG. 10 is a cross-sectional view of a thermal processing
apparatus having a cross-flow injector system according to an
embodiment of the present invention;
[0037] FIG. 11 is a cross-sectional side view of a portion of the
thermal processing apparatus of FIG. 10 showing positions of
injector orifices in relation to the liner and of exhaust slots in
relation to the wafers according to an embodiment of the present
invention;
[0038] FIG. 12 is a plan view of a portion of the thermal
processing apparatus of FIG. 10 taken along the line A-A of FIG. 10
showing gas flow from orifices of a primary and a secondary
injector across a wafer and to an exhaust port according to an
embodiment of the present invention;
[0039] FIG. 13 is a plan view of a portion of the thermal
processing apparatus of FIG. 10 taken along the line A-A of FIG. 10
showing gas flow from orifices of a primary and a secondary
injector across a wafer and to an exhaust port according to another
embodiment of the present invention;
[0040] FIG. 14 is a plan view of a portion of the thermal
processing apparatus of FIG. 10 taken along the line A-A of FIG. 10
showing gas flow from orifices of a primary and a secondary
injector across a wafer and to an exhaust port according to yet
another embodiment of the present invention;
[0041] FIG. 15 is a plan view of a portion of the thermal
processing apparatus of FIG. 10 taken along the line A-A of FIG. 10
showing gas flow from orifices of a primary and a secondary
injector across a wafer and to an exhaust port according to still
another embodiment of the present invention;
[0042] FIG. 16 is a cross-sectional view of a thermal processing
apparatus having an alternative up-flow injector system according
to an embodiment of the present invention;
[0043] FIG. 17 is a cross-sectional view of a thermal processing
apparatus having an alternative down-flow injector system according
to an embodiment of the present invention;
[0044] FIG. 18 is flowchart showing an embodiment of a process for
thermally processing a batch of wafers according to an embodiment
of the present invention whereby each wafer of the batch of wafers
is quickly and uniformly heated to the desired temperature; and
[0045] FIG. 19 is flowchart showing another embodiment of a process
for thermally processing a batch of wafers according to an
embodiment of the present invention whereby each wafer of the batch
of wafers is quickly and uniformly heated to the desired
temperature.
[0046] FIG. 20 is a cross-sectional view of a thermal processing
apparatus including an injection system according to one embodiment
of the present invention.
[0047] FIG. 21 shows an elongated tube having a plurality of
injection ports in accordance with one embodiment of the present
invention.
[0048] FIG. 22 is a partial cross-sectional side view of a thermal
processing apparatus showing connection of the injection system
with a cross-flow liner and a base plate in accordance with one
embodiment of the present invention.
[0049] FIG. 23 is a partial cross-sectional top view of a thermal
processing apparatus showing connection of the injection system
with a cross-flow liner and a base plate in accordance with one
embodiment of the present invention.
[0050] FIG. 24 is a partial plan view of a liner top plate showing
openings having notches.
[0051] FIG. 25 is an external view of a cross-flow stepped liner
showing a longitudinal bulging section according to one embodiment
of the present invention.
[0052] FIG. 26 is an external view of a cross-flow stepped liner
showing a plurality of exhaust slots in the liner according to one
embodiment of the present invention.
[0053] FIG. 27 is a plan view of an injection system with a
cross-flow liner having a bulging section showing gas flow from
orifices that impinges the liner inner wall prior to flowing across
a wafer and exiting an exhaust slot according to one embodiment of
the present invention.
[0054] FIG. 28 is a plan view of an injection system with a
cross-flow liner having a bulging section showing gas flow from
orifices that impinges each other prior to flowing across a wafer
and exiting an exhaust slot according to one embodiment of the
present invention.
[0055] FIG. 29 is a plan view of an injection system with a
cross-flow liner having a bulging section showing gas flow from
orifices directing to the center of a wafer and exiting an exhaust
slot according to one embodiment of the present invention.
[0056] FIG. 30 is CFD demonstration for a thermal processing
apparatus including an injection system having injection ports
facing the center of a substrate in accordance with one embodiment
of the present invention for deposition of silicon nitride.
[0057] FIG. 31 is CFD demonstration for a thermal processing
apparatus including an injection system having injection ports
facing each other in accordance with one embodiment of the present
invention for deposition of silicon nitride.
[0058] FIG. 32 is CFD demonstration for a thermal processing
apparatus including an injection system having injection ports
facing the liner inner wall in accordance with one embodiment of
the present invention for deposition of aluminum oxide.
DETAILED DESCRIPTION
[0059] The present invention is directed to an apparatus and method
for processing a relatively small number or mini-batch of one or
more work pieces, such as semiconductor substrates or wafers, held
in a carrier, such as a cassette or boat, that provides reduced
processing cycle times and improved process uniformity.
[0060] As used herein the term "mini-batch" means a number of
wafers less than the hundreds of wafers found in the typical batch
systems, and preferably in the range of from one to about
fifty-three semiconductor wafers or wafers, of which from one to
fifty are product wafers and the remainder are non-product wafers
used for monitoring purposes and as baffle wafers.
[0061] By thermal processing it is meant processes that in which
the work piece or wafer is heated to a desired temperature which is
typically in the range of about 350.degree. C. to 1300.degree. C.
Thermal processing of semiconductor wafers can include, for
example, heat treating, annealing, diffusion or driving of dopant
material, deposition or growth of layers of material, such as
chemical vapor deposition or CVD, and etching or removal of
material from the wafers.
[0062] A thermal processing apparatus according to an embodiment
will now be described with reference to FIG. 1. For purposes of
clarity, many of the details of thermal processing apparatuses that
are widely known and are widely known to a person of skill in the
art have been omitted. Such detail is described in more detail in,
for example, commonly assigned U.S. Pat. No. 4,770,590, which is
incorporated herein by reference.
[0063] FIG. 1 is a cross-sectional view of an embodiment of a
thermal processing apparatus for thermally processing a batch of
semiconductor wafers. As shown, the thermal processing apparatus
100, generally includes a vessel 101 that encloses a volume to form
a process chamber 102 having a support 104 adapted for receiving a
carrier or boat 106 with a batch of wafers 108 held therein, and
heat source or furnace 110 having a number of heating elements
112-1, 112-2 and 112-3 (referred to collectively hereinafter as
heating elements 112) for raising a temperature of the wafers to
the desired temperature for thermal processing. The thermal
processing apparatus 100 further includes one or more optical or
electrical temperature sensing elements, such as a resistance
temperature device (RTD) or thermal couple (T/C), for monitoring
the temperature within the process chamber 102 and/or controlling
operation of the heating elements 112. In the embodiment shown the
temperature sensing element is a profile T/C 114 that has multiple
independent temperature sensing nodes or points (not shown) for
detecting the temperature at multiple locations within the process
chamber 102. The thermal processing apparatus 100 can also include
one or more injectors 116 (only one of which is shown) for
introducing a fluid, such as a gas or vapor, into the process
chamber 102 for processing and/or cooling the wafers 108, and one
or more purge ports or vents 118 (only one of which is shown) for
introducing a gas to purge the process chamber and/or to cool the
wafers. A liner 120 increases the concentration of processing gas
or vapor near the wafers 108 in a region or process zone 128 in
which the wafers are processed, and reduces contamination of the
wafers from flaking or peeling of deposits that can form on
interior surfaces of the process chamber 102. Processing gas or
vapor exits the process zone through exhaust ports or slots 121 in
the chamber liner 120.
[0064] Generally, the vessel 101 is sealed by a seal, such as an
o-ring 122, to a platform or base-plate 124 to form the process
chamber 102, which completely encloses the wafers 108 during
thermal processing. The dimensions of the process chamber 102 and
the base-plate 124 are selected to provide a rapid evacuation,
rapid heating and a rapid backfilling of the process chamber.
Advantageously, the vessel 101 and the base-plate 124 are sized to
provide a process chamber 102 having dimensions selected to enclose
a volume substantially no larger than necessary to accommodate the
carrier 106 with the wafers 108 held therein. Preferably, the
vessel 101 and the base-plate 124 are sized to provide a process
chamber 102 having dimensions of from about 125 to about 150% of
that necessary to accommodate the carrier 106 with the wafers 108
held therein, and more preferably, the process chamber has
dimensions no larger than about 125% of that necessary to
accommodate the carrier and the wafers in order to minimize the
chamber volume which aids in pump down and back-fill time
required.
[0065] Openings for the injectors 116, T/Cs 114 and vents 118 are
sealed using seals such as o-rings, VCR.RTM., or CF.RTM. fittings
Gases or vapor released or introduced during processing are
evacuated through a foreline or exhaust port 126 formed in a wall
of the process chamber 102 (not shown) or in a plenum 127 of the
base-plate 124, as shown in FIG. 1. The process chamber 102 can be
maintained at atmospheric pressure during thermal processing or
evacuated to a vacuum as low as 5 millitorr through a pumping
system (not shown) including one or more roughing pumps, blowers,
hi-vacuum pumps, and roughing, throttle and foreline valves.
[0066] In another embodiment, shown in FIG. 2, the base-plate 124
further includes a substantially annular flow channel 129 adapted
to receive and support an injector 116 including a ring 131 from
which depend a number of vertical injector tube or injectors 116A.
The injectors 116A can be sized and shaped to provide an up-flow,
down flow or cross-flow flow pattern, as described below. The ring
131 and injectors 116A are located so as to inject the gas into the
process chamber 102 between the boat 106 and the vessel 101. In
addition, the injectors 116A are spaced apart around the ring 131
to uniformly introduce process gas or vapor into the process
chamber 102, and may, if desired, be used during purging or
backfilling to introduce a purge gas into the process chamber. The
base-plate 124 is sized in a short cylindrical form with an
outwardly extending upper flange 133, a sidewall 135, and an
inwardly extending base 137. The upper flange 133 is adapted to
receive and support the vessel 101, and contains an o-ring 122 to
seal the vessel to the upper flange. The base 137 is adapted to
receive and support the liner 120 outside of where the ring 131 of
injectors 116 is supported.
[0067] Additionally, the base-plate 124 shown in FIG. 2
incorporates various ports including backfill/purge gas inlet ports
139, 143, cooling ports 145,147, provided to circulate cooling
fluid in the base-plate 124, and a pressure monitoring port 149 for
monitoring pressure within the process chamber 102. Process gas
inlet ports 151, 161, introduce a gas from a supply (not shown) to
the injectors 116. The backfill/purge ports 139,143, are provided
at the sidewall 135 of the base-plate 124 principally to introduce
a gas from a vent/purge gas supply (not shown) to the vents 118. A
mass flow controller (not shown) or any other suitable flow
controller is placed in line between the gas supplies and the ports
139, 143, 151 and 161 to control the gas flow into the process
chamber 102.
[0068] The vessel 101 and liner 120 can be made of any metal,
ceramic, crystalline or glass material that is capable of
withstanding the thermal and mechanical stresses of high
temperature and high vacuum operation, and which is resistant to
erosion from gases and vapors used or released during processing.
Preferably, the vessel 101 and liner 120 are made from an opaque,
translucent or transparent quartz glass having a sufficient
thickness to withstand the mechanical stresses and that resists
deposition of process byproducts, thereby reducing potential
contamination of the processing environment. More preferably, the
vessel 101 and liner 120 are made from quartz that reduces or
eliminates the conduction of heat away from the region or process
zone 128 in which the wafers 108 are processed.
[0069] The batch of wafers 108 is introduced into the thermal
processing apparatus 100 through a load lock or loadport (not
shown) and then into the process chamber 102 through an access or
opening in the process chamber or base-plate 124 capable of forming
a gas tight seal therewith. In the configuration shown in FIG. 1,
the process chamber 102 is a vertical reactor and the access
utilizes a movable pedestal 130 that is raised during processing to
seal with a seal, such as an o-ring 132 on the base-plate 124, and
lowered to enable an operator or an automated handling system, such
as a boat handling unit (BHU) (not shown), to position the carrier
or boat 106 on the support 104 affixed to the pedestal.
[0070] The heating elements 112 include elements positioned
proximal to a top 134 (elements 112-3), side 136 (elements 112-2)
and bottom 138 (elements 112-1) of the process chamber 102.
Advantageously, the heating elements 112 surround the wafers to
achieve a good view factor of the wafers and thereby provide an
isothermal control volume or process zone 128 in the process
chamber in which the wafers 108 are processed. The heating elements
112-1 proximal to the bottom 138 of the process chamber 102 can be
disposed in or on the pedestal 130. If desired, additional heating
elements may be disposed in or on the base plate 124 to supplement
heat from the heating elements 112-1.
[0071] In the embodiment shown in FIG. 1 the heating elements 112-1
proximal to the bottom of the process chamber preferably are
recessed in the movable pedestal 130. The pedestal 130 is made from
a thermally and electrically insulating material or insulating
block 140 having an electric, resistive heating elements 112-1
embedded therein or affixed thereto. The pedestal 130 further
includes one or more feedback sensors or T/Cs 141 used to control
the heating elements 112-1. In the configuration shown, the T/Cs
141 are embedded in the center of the insulating block 140.
[0072] The side heating elements 112-2 and the top heating elements
112-3 may be disposed in or on an insulating block 110 about the
vessel 101. Preferably the side heating elements 112-2 and the top
heating elements 112-3 are recessed in the insulating block
110.
[0073] The heating elements 112 and the insulating blocks 110 and
140 may be configured in any of a variety of ways and may be made
in any of a variety of ways and with any of a variety of
materials.
[0074] Preferably, to attain desired processing temperatures of up
to 1150.degree. C. the heating elements 112-1 proximal to the
bottom 138 of the process chamber 102 have a maximum power output
of from about 0.1 kW to about 10 kW with a maximum process
temperature of at least 1150.degree. C. More preferably, these
bottom heating elements 112-1 have a power output of at least about
3.8 kW with a maximum process temperature of at least 950.degree.
C. In one embodiment, the side heating elements 112-2 are
functionally divided into multiple zones, including a lower zone
nearest the pedestal 130 and upper zone, each of which are capable
of being operated independently at different power levels and duty
cycles from each other and from the top heating elements 112-3 and
bottom heating elements 112-1.
[0075] The heating elements 112 are controlled in any suitable
manner, either by using a control technique of a type well known in
the art.
[0076] Contamination from the insulating block 140 and bottom
heating elements 112-1 is reduced if not eliminated by housing the
heating element and insulation block in an inverted quartz crucible
142, which serves as a barrier between the heating element and
insulation block and the process chamber 102. The crucible 142 is
also sealed against the loadport and BHU environment to further
reduce or eliminate contamination of the processing environment.
Generally, the interior of the crucible 142 is at standard
atmospheric pressure, so that the crucible 142 should be strong
enough to withstand a pressure differential between the process
chamber 102 and the pedestal 130 across the crucible 142 of as much
as 1 atmosphere.
[0077] While the wafers 108 are being loaded or unloaded, that is
while the pedestal 130 is in the lowered position (FIG. 3), the
bottom heating elements 112-1 are powered to maintain an idle
temperature lower than the desired processing temperature. For
example, for a process having a desired processing temperature for
the bottom heating elements of 950.degree. C., the idle temperature
can be from 50-150.degree.. The idle temperature can be set higher
for certain processes, such as those having a higher desired
processing temperature and/or higher desired ramp up rate, or to
reduce thermal cycling effects on the bottom heating elements
112-1, thereby extending element life.
[0078] In order to further reduce preprocessing time, that is the
time required to prepare the thermal processing apparatus 100 for
processing, the bottom heating elements 112-1 can be ramped to at
or below the desired process temperature during the push or load,
that is while the pedestal 130 with a boat 106 of wafers 108
positioned thereon is being raised. However, to minimize thermal
stresses on the wafers 108 and components of the thermal processing
apparatus 100 it is preferred to have the bottom heating elements
112-1 reach the desired process temperature at the same time as the
heating elements 112-3 and 112-2 located proximal to respectively
the top 134 and side 136 of the process chamber 102. Thus, for some
processes, such as those requiring higher desired process
temperatures, the temperature of the bottom heating elements 112-1
can begin being ramped up before the pedestal 130 begins being
raised, while the last of the wafers 108 in a batch are being
loaded.
[0079] Similarly, it will be appreciated that after processing and
during the pull or unload cycle, that is while the pedestal 128 is
being lowered, power to the bottom heating elements 112-1 can be
reduce or removed completely to begin ramping down the pedestal 130
to the idle temperature, in preparation for cooling of the wafers
108 and unloading by the BHU.
[0080] To assist in cooling the pedestal 130 to a pull temperature
prior to the pull or unload cycle, a purge line for air or an inert
purge gas, such as nitrogen, is installed through the insulating
block 140. Preferably, nitrogen is injected through a passage 144
through the center of the insulating block 140 and allowed to flow
out between the top of the insulating block 140 and the interior of
the crucible 142 to a perimeter thereof. The hot nitrogen is then
exhausted to the environment either through High Efficiency
Particulate Air (HEPA) filter (not shown) or to a facility exhaust
(not shown). This center injection configuration facilitates the
faster cooling of the center of the wafers 108, and therefore is
ideal to minimize the center/edge temperature differential of the
bottom wafer or wafers, which could otherwise result in damage due
to slip-dislocation of the crystal lattice structure.
[0081] As noted above, to increase or extend the life of bottom
heating element 112-1 the idle temperature can be set higher,
closer to the desired processing temperature to reduce the effects
of thermal cycling. In addition, it is also desirable to
periodically bake out the heating elements 112-1 in an oxygen rich
environment to promote the formation of a protective oxide surface
coat. For example, where the resistive heating elements are formed
from an Aluminum containing alloy, such as Kanthal.RTM., baking out
the heating elements 112-1 in an oxygen rich environment promotes
an alumna oxide surface growth. Thus, the insulating block 140 can
further include an oxygen line (not shown) to promote the formation
of the protective oxide surface coat during bake out of the heating
elements 112-1. Alternatively, oxygen for bake out can be
introduced through the purge line used during processing to supply
cooling nitrogen via a three-way valve.
[0082] FIG. 3 is a cross-sectional view of a portion of a thermal
processing apparatus 100. FIG. 3 shows the thermal processing
apparatus 100 while the wafers 108 are being loaded or unloaded,
that is while the pedestal 130 is in the lowered position. In this
mode of operation, the thermal processing apparatus 100 further
includes a thermal shield 146 that can be rotated or slid into
place above the pedestal 130 and the lower wafer 108 in the boat
106. To improve the performance of the thermal shield 146,
generally the thermal shield is reflective on the side facing the
heating elements 112-1 and absorptive on the side facing the wafers
108. Purposes of the thermal shield 146 include increasing the rate
of cooling of the wafers 108 lower down in the boat 106, and
assisting in maintaining the idle temperature of the pedestal 130
and bottom heating elements 112-1 to decrease the time required to
ramp up the process chamber 102 to the desired processing
temperature. An embodiment of a thermal processing apparatus having
a thermal shield will now be described in further detail with
reference to FIGS. 3 through 6.
[0083] FIG. 3 also shows an embodiment of a thermal processing
apparatus 100 having pedestal heating elements 112-1 and a thermal
shield 146. In the embodiment shown, the thermal shield 146 is
attached via arm 148 to a rotable shaft 150 that is turned by an
electric, pneumatic or hydraulic actuator to rotate the thermal
shield 146 into a first position between the heated pedestal 130
and the lowest of the wafers 108 in the boat 106 during the pull or
unload cycle, and removed or rotated to a second position not
between the pedestal and the wafers during at least a final portion
or end of the push or load cycle, just before the bottom of the
boat 106 enters into the chamber 102. Preferably, the rotable shaft
150 is mounted on or affixed to the mechanism (not shown) used for
raising and lowering the pedestal 130, thereby enabling the thermal
shield 146 to be rotated into position as soon as the top of the
pedestal has cleared the process chamber 102. Having the shield 146
in place during the load cycle enables the heating elements 112-1
to be heated to a desired temperature more rapidly than would
otherwise be possible. Similarly, during unload cycle the shield
146 helps in cooling the wafers, particularly those closer to the
pedestal, by reflect the heat radiating from the pedestal heating
elements 112-1.
[0084] Alternatively, the rotable shaft 150 can be a mounted on or
affixed to another part of the thermal processing apparatus 100 and
adapted to move axially in synchronization with the pedestal 130,
or to rotate the thermal shield 146 into position only when the
pedestal is fully lowered.
[0085] FIG. 4 is a diagrammatic illustration of the pedestal
heating elements 112-1 and thermal shield 146 of FIG. 3
illustrating the reflection of thermal energy or heat radiating
from the bottom heating elements back to the pedestal 130 and the
absorption of thermal energy or heat radiating from the lower wafer
108 in the batch or stack of wafers. It has been determined that
the desired characteristics, high reflectivity and high
absorptivity, can be obtained using a number of different
materials, such as metals, ceramic, glass or polymeric coatings,
either individually or in combination. By way of example the
following table list various suitable materials and corresponding
parameters.
1TABLE I Material Absorptivity Reflectivity Stainless Steel 0.2 0.8
Opaque Quartz 0.5 0.5 Polished Aluminum 0.03 0.97 Silicon Carbide
0.9 0.1
[0086] According to one embodiment the thermal shield 146 can be
made from a single material such as silicon-carbide (SiC), opaque
quartz or stainless steel which has been polished on one side and
scuffed, abraded or roughened on the other. Roughening a surface of
the thermal shield 146 can significantly change its heat transfer
properties, particularly its reflectivity.
[0087] In another embodiment, the thermal shield 146 can be made
from two different layers of material. FIG. 5 is a diagrammatic
illustration of a thermal shield 146 having a top layer 152 of
material such as SiC or opaque quartz, with a high absorptivity and
a lower layer 154 of material or metal, such as polished stainless
steel or polished aluminum, with a high reflectivity. Although
shown as having approximately equal thicknesses, it will be
appreciated that either the top layer 152 or the lower layer 154
can have a relatively greater thickness depending on specific
requirements for the thermal shield 146, such as minimizing thermal
stresses between the layers due to differences in coefficients of
thermal expansion. For example, in certain embodiments the lower
layer 154 can be an extremely thin layer or film of polished metal
deposited, formed or plated on a quartz plate that forms the top
layer 152. The materials can be integrally formed or interlocking,
or joined by conventional means such as bonding or fasteners.
[0088] In yet another embodiment, the thermal shield 146 further
includes an internal cooling channel 156 to further insulate the
wafers 108 from the bottom heating elements 112-1. In one version
of this embodiment, shown in FIG. 6, the cooling channel 156 is
formed between two different layers 152 and 154 of material. For
example, the cooling channel 156 can be formed by milling or any
other suitable technique in a highly absorptive opaque quartz layer
152, and be covered by a metal layer 154 or coating such as a
Titanium or Aluminum coating. Alternatively, the cooling channel
156 can be formed in the metal layer 154 or both the metal layer
and the quartz layer 152.
[0089] FIG. 7 is a perspective view of an embodiment of a thermal
shield assembly 153 including the thermal shield 146, arm 148,
rotable shaft 150 and an actuator 155.
[0090] As shown in FIG. 8, the thermal processing apparatus 100
further includes a shutter 158 that can be rotated or slid or
otherwise moved into place above the boat 106 to isolate the
process chamber 102 from the outside or load port environment when
the pedestal 130 is in the fully lowered position. For example, the
shutter 158 can be slid into place above the carrier 106 when the
pedestal 130 is in a lowered position, and raised to isolate the
process chamber 102. Alternatively, the shutter 158 can be rotated
or swung into place above the carrier 106 when the pedestal 130 is
in a lowered position, and subsequently raised to isolate the
process chamber 102. Optionally, the shutter 158 may be rotated
about or relative to threaded screw or rod to simultaneously raise
the shutter to isolate the process chamber 102 as it is swung into
place above the carrier 106.
[0091] For a process chamber 102 that is normally operated under
vacuum, such as in a CVD system, the shutter 158 could form a
vacuum seal against the base-plate 124 to allow the process chamber
102 to be pumped down to the process pressure or vacuum. For
example, it may be desirable to pump down the process chamber 102
between sequential batches of wafers to reduce or eliminate the
potential for contaminating the process environment. Forming a
vacuum seal is preferably done with a large diameter seal, such as
an o-ring, and thus the shutter 158 can desirably include a number
of water channels 160 to cool the seal. In the embodiment shown in
FIG. 8 the shutter 158 seals with the same o-ring 132 used to seal
with the crucible 142 when the pedestal 130 is in the raised
position.
[0092] For a thermal processing apparatus 130 in which the process
chamber 102 is normally operated at atmospheric pressure, the
shutter 158 is simply an insulating plug designed to reduce heat
loss from the bottom of the process chamber. One embodiment for
accomplishing this involves the use of an opaque quartz plate,
which may or may not further include a number of cooling channels
underneath or internal thereto.
[0093] When the pedestal 130 is in the fully lowered position, the
shutter 158 is moved into position below the process chamber 102
and then raised to isolate the process chamber by one or more
electric, hydraulic or pneumatic actuators (not shown). Preferably,
the actuators are pneumatic actuators using from about 15 to 60
pounds per square inch gauge (PSIG) air, which is commonly
available on thermal processing apparatus 100 for operation of
pneumatic valves. For example, in one version of this embodiment
the shutter 158 can comprise a plate having a number of wheels
attached via short arms or cantilevers to two sides thereof. In
operation, the plate or shutter 158 is rolled into position beneath
the process chamber 102 on two parallel guide rails. Stops on the
guide rails then cause the cantilevers to pivot translating the
motion of the shutter 158 into an upward direction to seal the
process chamber 102.
[0094] As shown in FIG. 9, the thermal processing apparatus 100
further includes a magnetically coupled wafer rotation system 162
that rotates the support 104 and the boat 106 along with the wafers
108 supported thereon during processing. Rotating the wafers 108
during processing improves within wafer (WIW) uniformity by
averaging out any non-uniformities in the heating elements 112 and
in process gas flows to create a uniform on-wafer temperature and
species reaction profile. Generally, the wafer rotation system 162
is capable of rotated the wafers 108 at a speed of from about 0.1
to about 10 revolutions per minute (RPM).
[0095] The wafer rotation system 162 includes a drive assembly or
rotating mechanism 164 having a rotating motor 166, such as an
electric or pneumatic motor, and a magnet 168 encased in a
chemically resistive container, such as annealed
polytetrafluoroethylene or stainless steel. A steel ring 170
located just below the insulating block 140 of the pedestal 130,
and a drive shaft 172 with the insulating block transfer the
rotational energy to another magnet 174 located above the
insulating block in a top portion of the pedestal. The steel ring
170, drive shaft 172 and second magnet 174 are also encased in a
chemically resistive container compound. The magnet 174 located in
the side of the pedestal 130 magnetically couples through the
crucible 142 with a steel ring or magnet 176 embedded in or affixed
to the support 104 in the process chamber 102.
[0096] Magnetically coupling the rotating mechanism 164 through the
pedestal 130 eliminates the need for locating it within the
processing environment or for having a mechanical feedthrough,
thereby eliminating a potential source of leaks and contamination.
Furthermore, locating rotating mechanism 164 outside and at some
distance from the processing minimizes the maximum temperature of
to which it is exposed, thereby increasing the reliability and
operating life of the wafer rotation system 162.
[0097] In addition to the above, the wafer rotation system 162 can
further include one or more sensors (not shown) to ensure proper
boat 106 position and proper magnetic coupling between the steel
ring or magnet 176 in the process chamber 102 and the magnet 174 in
the pedestal 130. A sensor which determines the relative position
of the boat 106, or boat position verification sensor, is
particularly useful. In one embodiment, the boat position
verification sensor includes a sensor protrusion (not shown) on the
boat 106 and an optical or laser sensor located below the
base-plate 124. In operation, after the wafers 108 have been
processed and the pedestal 130 is lowered about 3 inches below the
base-plate 124. There, the wafer rotation system 162 is commanded
to turn the boat 106 until the boat sensor protrusion can be seen.
Then, the wafer rotation system 162 is operated to align the boat
so that the wafers 108 can be unloaded. After this is done, the
boat is lowered to the load/unload height. After the initial check,
it is only capable of verifying the boat location from the flag
sensor.
[0098] As shown in FIG. 10, improved injectors 216 are preferably
used in the thermal processing apparatus 100. The injectors 216 are
distributive or cross(X)-flow injectors 216-1 in which process gas
or vapor is introduced through injector openings or orifices 180 on
one side of the wafers 108 and boat 106 and caused to flow across
the surfaces of the wafers in a laminar flow to exit exhaust ports
or slots 182 in the chamber line 120 on opposite the side. X-flow
injectors 116-1 improve wafer 108 to wafer uniformity within a
batch of wafers 108 by providing an improved distribution of
process gas or vapor over earlier up-flow or down flow
configurations.
[0099] Additionally, X-flow injectors 216 can serve other purposes,
including the injection of gases for cool-down (e.g., helium,
nitrogen, hydrogen) for forced convective cooling between the
wafers 108. Use of X-flow injectors 216 results in a more uniform
cooling between wafers 108 whether disposed at the bottom or top of
the stack or batch and those wafers that are disposed in the
middle, as compared with earlier up-flow or down flow
configurations. Preferably, the injector 216 orifices 180 are
sized, shaped and position to provide a spray pattern that promotes
forced convective cooling between the wafers 108 in a manner that
does not create a large temperature gradient across the wafer.
[0100] FIG. 11 is a cross-sectional side view of a portion of the
thermal processing apparatus 100 of FIG. 10 showing illustrative
portions of the injector orifices 180 in relation to the chamber
liner 120 and the exhaust slots 182 in relation to the wafers
108.
[0101] FIG. 12 is a plan view of a portion of the thermal
processing apparatus 100 of FIG. 10 taken along the line A-A of
FIG. 10 showing laminar gas flow from the orifices 180-1 and 180-2
of primary and secondary injectors 184, 186, across an illustrative
one of the wafers 108 and to exhaust slots 182-1 and 182-2
according to one embodiment. It should be noted that the position
of the exhaust slot 182 as shown in FIG. 10 have been shifted from
the position of exhaust slots 182-1 and 182-2 shown in FIG. 12 to
allow illustration of the exhaust slot and injector 116-1 in a
single a cross-sectional view of a thermal processing apparatus. It
should also be noted that the dimensions of the injectors 184, 186,
and the exhaust slots 182-1 and 182-2 relative to the wafer 108 and
the chamber liner 120 have been exaggerated to more clearly
illustrate the gas flow from the injectors to the exhaust
slots.
[0102] Also as shown in FIG. 12, the process gas or vapor is
initially directed away from the wafers 108 and toward the liner
120 to promote mixing of the process gas or vapor before it reaches
the wafers. This configuration of orifices 180-1 and 180-2 is
particularly useful for processes or recipes in which different
reactants are introduced from each of the primary and secondary
injectors 184, 186, for example to form a multi-component film or
layer.
[0103] FIG. 13 is another plan view of a portion of the thermal
processing apparatus 100 of FIG. 10 taken along the line A-A of
FIG. 10 showing an alternative gas flow path from the orifices 180
of the primary and secondary injector 184, 186, across an
illustrative on of the wafer 108 and to the exhaust slots 182
according to another embodiment.
[0104] FIG. 14 is another plan view of a portion of the thermal
processing apparatus 100 of FIG. 10 taken along the line A-A of
FIG. 10 showing an alternative gas flow path from the orifices 180
of the primary and secondary injector 184, 186, across an
illustrative on of the wafer 108 and to the exhaust slots 182
according to yet another embodiment.
[0105] FIG. 15 is another plan view of a portion of the thermal
processing apparatus 100 of FIG. 10 taken along the line A-A of
FIG. 10 showing an alternative gas flow path from the orifices 180
of the primary and secondary injector 184, 186, across an
illustrative on of the wafer 108 and to the exhaust slots 182
according to still another embodiment.
[0106] FIG. 16 is a cross-sectional view of a thermal processing
apparatus 100 having two or more up-flow injectors 116-1 and 116-2
according to an alternative embodiment. In this embodiment, process
gas or vapor admitted from the process injectors 116-1 and 116-2
having respective outlet orifices low in the process chamber 102
flows up and across the wafers 108, and spent gases exit exhaust
slots 182 in the top of the liner 120. An up-flow injector system
is also shown in FIG. 1.
[0107] FIG. 17 is a cross-sectional view of a thermal processing
apparatus 100 having a down-flow injector system according to an
alternative embodiment. In this embodiment, process gas or vapor
admitted from process injectors 116-1 and 116-2 having respective
orifices high in the process chamber 102 flows down and across the
wafers 108, and spent gases exit exhaust slots 182 in the lower
portion of the liner 120.
[0108] Advantageously, the injectors 116, 216, and/or the liner 120
can be quickly and easily replaced or swapped with other injectors
and liners having different points for the injection and exhausting
of the process gas from the process zone 128. It will be
appreciated by those skilled in the art that the embodiment of the
x-flow injector 216 shown in FIG. 10 adds a degree of process
flexibility by enabling the flow pattern within the process chamber
102 to be quickly and easily changed from a cross-flow
configuration, as shown in FIG. 10, to an up-flow configuration, as
shown in FIGS. 1 and 16, or a down-flow configuration, as shown in
FIG. 17. This can be accomplished through the use of easily
installable injector assemblies 216 and liners 120 to convert the
flow geometry from cross-flow to an up-flow or down-flow.
[0109] The injectors 116, 216, and the liner 120 can be separate
components, or the injector can be integrally formed with liner as
a single piece. The latter embodiment is particular useful in
applications where it is desirable to frequently change the process
chamber 102 configuration.
[0110] An illustrative method or process for operating the thermal
processing apparatus 100 is described with reference to FIG. 18.
FIG. 18 is a flowchart showing steps of a method for thermally
processing a batch of wafers 108 wherein each wafer of the batch of
wafers is quickly and uniformly heated to the desired temperature.
In the method, the pedestal 130 is lowered, and the thermal shield
142 is moved into a position while the pedestal 130 is lowered to
reflect heat from the bottom heating element 112-1 back to the
pedestal 130 to maintain the temperature thereof, and to insulate
the finished wafers 108 (step 190). Optionally, the shutter 158 is
moved into position to seal or isolate the process chamber 102
(step 192), and power is applied to the heating elements 112-2,
112-3, to begin pre-heating the process chamber 102 to or maintain
at an intermediate or idling temperature (step 194). A carrier or
boat 106 loaded with new wafers 108 is positioned on the pedestal
130 (step 196). The pedestal 130 is raised to position the boat in
the process zone 128, while simultaneously removing the shutter
158, the thermal shield 142, and ramping-up the bottom heating
element 112-1 to preheat the wafers to an intermediate temperature
(step 197). Preferably, the thermal shield 142 is removed just
before the boat 106 is positioned in the process zone 128. A fluid,
such as a process gas or vapor, is introduced on one side of the of
wafers 108 through a plurality of injection ports 180 (step 198).
The fluid flows from the injection ports 180 across surfaces of the
wafers 108 to exhaust ports 182 positioned in the liner 120 on the
opposite side of the wafers relative to the injection ports (step
199). Optionally, the boat 106 can be rotated within the process
zone 128 during thermal processing of the batch of wafers 108 to
further enhance uniformity of the thermal processing, by
magnetically coupling mechanical energy through the pedestal 130 to
the carrier or boat 106 to reposition it during thermal processing
of the wafers (step 200).
[0111] A method or process for a thermal processing apparatus 100
according to another embodiment will now be described with
reference to FIG. 19. FIG. 19 is a flowchart showing steps of an
embodiment of a method for thermally processing a batch of wafers
108 in a carrier. In the method, an apparatus 100 is provided
having a process chamber 102 with dimensions and a volume not
substantially larger than necessary (guard heaters absent) to
accommodate the carrier 106 with the wafers 108 held therein. The
pedestal 130 is lowered, and the boat 106 with the wafers 108 held
therein positioned thereon (step 202). The pedestal 130 is raised
to insert the boat in the process chamber 102, while simultaneously
preheating the wafers 108 to an intermediate temperature (step
204). Power is applied to the heating elements 112-1, 112-2, 112-3,
each disposed proximate to at least one of the top wall 134, the
side wall 136 and the bottom wall 138 of the process chamber 102 to
begin heating the process chamber (step 206). Optionally, power to
at least one of the heating elements is adjusted independently to
provide a substantially isothermal environment at a desired
temperature in a process zone 128 in the process chamber 102 (step
208). When the wafers 108 have been thermally processed, and while
maintaining the desired temperature in the process zone 128, the
pedestal 130 is lowered, and the thermal shield 142 is moved into
position to insulate the finished wafers 108 and to reflect heat
from the bottom heating element 112-1 back to the pedestal 130 to
maintain the temperature thereof (step 210). Also, optionally, the
shutter 158 is moved into position to seal or isolate the process
chamber 102, and power applied to the heating elements 112-2,
112-3, to maintain the temperature of the process chamber (step
212). The boat 106 is then removed from the pedestal 130 (step
214), and another boat loaded with a new batch of wafers to be
processed positioned on the pedestal (step 216). The shutter 158 is
repositioned or removed (step 218), and the thermal shield
withdrawn or repositioned to preheat the wafers 108 in the boat 106
to an intermediate temperature while simultaneously raising the
pedestal 130 to insert the boat into the process chamber 102 to
thermally process the new batch of wafers (step 220).
[0112] It has been determined that the thermal processing apparatus
100 provided and operated as described above, reduces the
processing or cycle time by about 75% over conventional systems.
For example, a conventional large batch thermal processing
apparatus may process 100 product wafers in about 232 minutes,
including pre-processing and post-processing time. The inventive
thermal processing apparatus 100 performs the same processing on a
mini-batch of 25 product wafers 108 in about 58 minutes.
[0113] An injection system in accordance with one embodiment of the
present invention will be now described with reference to FIGS. 20
through 32.
[0114] Injectors having injection ports or orifices distributed in
elongated tubes have been used in both horizontal and vertical
furnaces to control gas concentration across the surface of
substrates. Typically, two or more injectors are used to distribute
similar or different gases depending on specific applications. For
example, for deposition of P-doped polysilicon, injectors with
distributed injection ports have been used to introduce PH.sub.3
gas across a wafer load in a furnace to provide a uniform gas
concentration. Injectors with distributed injection ports are used
to ensure that the properties of the deposited films are the same
across the wafer load. Traditionally, the injectors are fixed,
i.e., the direction of injection ports or orifices in the injectors
are fixed and typically face toward the center of wafers. Even so,
films deposited on the wafers still exhibit an undesirable
within-wafer uniformity. The uniformity, quality and repeatability
of deposited films depend on not only gas flow rates,
concentration, pressure and temperature, but also gas flow pattern
and distribution of gases. The present invention provides an
injection system that is angularly adjustable to promote the
momentum transfer of "ballistic mixing" of different gases to
provide improved flow uniformity and thus improved quality and
uniformity of the deposited films. In general, the injection system
of the present invention comprises one or more elongated injection
tubes having a plurality of injection ports or orifices distributed
in the tubes for directing flow of reactant and other gases across
the surface of each substrate. The elongated injection tubes are
rotatable about an axis in 360 degrees.
[0115] FIG. 20 shows a thermal processing apparatus 230 including
an injection system 250 according to one embodiment of the present
invention. To simplify description of the invention, elements not
closely relevant to the invention are not indicated in the drawing
and described. In general, the apparatus 230 includes a vessel 234
that houses a process chamber 236 having a support 238 adapted for
receiving a carrier 240 with a batch of wafers 242 held therein.
The apparatus 230 includes heat source or furnace 244 for raising
temperature of the wafers 242 to the desired temperature for
thermal processing. A cross-flow liner 232 is provided to increase
the concentration of processing gas or vapor near wafers 242 and
reduce contamination of wafers 242 from flaking or peeling of
deposits that can form on interior surfaces of the process chamber
236. The liner 232 is patterned to conform to the contour of the
wafer carrier 240 and sized to reduce the gap between the wafer
carrier 240 and the liner wall. The liner 232 is mounted to the
base plate 246 and sealed. A cross-flow injection system 250 is
disposed between the liner 232 and the wafer carrier 240. Gases are
introduced through a plurality of injection ports or orifices 252
from one side of the wafers 242 and carrier 240 across the surface
of the wafers in a laminar flow as described below. A plurality of
slots 254 are formed in the liner 232 on the opposite side to
exhaust gases or reaction by-product.
[0116] The cross-flow injection system 250 includes one or more
elongated injection tubes. FIG. 21 shows an elongated injection
tube 256 according to one embodiment of the present invention. As
shown, a plurality of injection ports or orifices 252 are provided
in the elongated injection tube 256. In one embodiment, the spacing
between the injection ports 252 is such that when the injection
tube 256 is installed, each injection port 252 is positioned at a
height between two adjacent wafers 242 supported in the wafer
carrier 240 so that the gas exiting the injection port 252 is
caused to flow in a path formed between the adjacent wafers. In
another embodiment, the spacing between and number of the injection
ports or orifices 252 in the injection tubes 256 cooperates with
the spacing between and number of slots 254 in the liner 232 so
that excessive gas or reaction by-products are exhausted from the
corresponding slot in the liner. The injection system 250 of the
present invention may comprise one or more elongated injection
tubes 256 as illustrated in FIG. 21. The elongated injection tube
256 can be made of any metal, ceramic, crystalline or glass
material that is capable of withstanding the thermal and mechanical
stresses of high temperature and high vacuum operation, and which
is resistant to erosion from gases and vapors used or released
during processing. Preferably, the injection tube is made from an
opaque, translucent or transparent quartz glass. In one embodiment,
the injection tube is made from quartz.
[0117] FIG. 22 is a partial cross-sectional view of a thermal
processing apparatus 230 showing connection of the injection system
250 with liner 232 and base plate 246. The elongated injection tube
256 is coupled to an injection inlet 262 in the base plate 246 and
sealed to the base plate by O-rings 264. The elongated injection
tubes 256 are engaged with the liner 232 through a clamp block 266,
as shown in detail in FIG. 23. A lock pin 268 locks the clamp block
266 to the base plate 246. Reactants or other gases are introduced
into the injection tube 256 through inlet 262.
[0118] FIG. 24 is a partial plan view of a top plate 270 of a liner
232 having openings 272 for receiving one or more elongated
injection tubes 256. As shown, the openings 272 in the top plate
270 are provided with notches 274 for stabilizing the elongated
injection tubes 256 and orienting the injection ports 252 in the
tubes 256 to a specific direction. While three notches 274A-C are
shown in each of the openings 272 for illustrative purpose, it
should be noted that any number of notches can be provided so that
the elongated injection tubes 256 can be rotated and adjusted about
an axis in 360 degrees and the injection ports 258 can be oriented
in any direction as desired. In one embodiment, the elongated tube
256 includes an index pin (not shown) for locking the elongated
tube 256 in one of the notches 274 in the opening 272. In another
embodiment, the injection ports or orifices 252 in the tubes 256
are formed in line with the index pin. Thus, when the elongated
tube 256 is installed, the index pin is locked in one of the
notches 274 and the injection ports 252 in the tube 256 are
oriented to a direction as indicated by the index pin locked in the
notch.
[0119] For example, when the index pin in the elongated tube 256 is
locked in notch 274A, the injection ports 252 are oriented to face
the inner surface of the liner 232. Gases exiting the injection
ports 252 impinge the wall and mix prior to flowing across the
surface of each substrate 242. In another embodiment, the index pin
in the elongated tube 256 is locked in notch 274B. The injection
ports 252 in each injection tube 256 are oriented to face each
other. Gases exiting the injection ports 252 impinge each other and
mix prior to flowing across the surface of each substrate 242. In a
further embodiment, the index pin in the elongated tube 256 is
locked in notch 274C so that the injection ports 252 are oriented
to face the center of the substrate 242. The number of notches
formed in the openings can be as many as desired so that the
elongated tube 256 can be rotated in 360 degrees and stabilized in
a desired position, and accordingly the injection ports 252 can be
oriented to a desired direction.
[0120] Of advantage, the injection system of the present invention
enables full freedom of rotation of the injection ports to promote
the momentum transfer of "ballistic mixing" of gases, which may
vary in different processes. The orientation of the injection ports
or orifices that influence gas mixing and flow direction can be
adjusted on a run-to-run basis without the need of process chamber
modification.
[0121] In one embodiment, the injection system of the present
invention is used in connection with a cross flow liner having a
bulging section. U.S. application Ser. No. ______ (Attorney Docket
No. 33586/US/1) filed currently with this application further
describes a cross-flow liner, the disclosure of which is hereby
incorporated by reference in its entirety. FIGS. 25-26 show a
cross-flow liner 276 that can be used in connection with the
injection system 250 of the present invention. As shown, the
cross-flow liner 276 includes a cylinder 278 having a close end 280
and open end 282. The cylinder 278 is provided with a longitudinal
bulging section 284 to accommodate a cross-flow injection system
250. A plurality of latitudinal slots 286 are provided
longitudinally in the cylinder 278 on the side opposite to the
bulging section 284 to exhaust gases and reaction by-products. The
cross-flow liner 276 is sized and patterned to conform to the
contour of the wafer carrier 240 and the carrier support 238. In
one embodiment, the liner 276 comprises a first section 288 sized
to conform to the wafer carrier 240 and a second section 290 sized
to conform to the carrier support 238. The diameter of the first
section 288 may differ from the diameter of the second section 290,
i.e., the liner 276 may be "stepped" to conform to the wafer
carrier 240 and carrier support 238 respectively. In one
embodiment, the first section 288 of the liner 276 has an inner
diameter that constitutes about 104 to 110% of the carrier outer
diameter. In another embodiment, the second section 290 of the
liner 276 has an inner diameter that constitutes about 115 to 120%
of outer diameter of the carrier support 238. The second section
290 may be provided with one or more heat shields to protect seals
such as O-rings from being overheated by heating elements. Of
advantage, the cross-flow liner 276 with a longitudinal bulging
section 284 can be made conformal to the contour of the wafer
carrier 240 to reduce the gap between the liner 276 and the wafer
carrier 240. This helps reduce vortices and stagnation in the gap
regions between the liner inner wall and the wafer carrier, and
thus improve flow uniformity, which in turn improves the quality,
uniformity, and repeatability of the deposited film.
[0122] In one embodiment shown in FIG. 27, two elongated injection
tubes 256 are installed in a bulging section 284 of a cross-flow
liner 276. The elongated tubes 256 are rotated and adjusted so that
the injection ports 252 are oriented to face the inner surface of
the liner 276. As shown in FIG. 27, gases exiting the injection
ports 252 impinge the liner wall and mix in the bulging section 284
prior to flowing across the surface of each substrate 242. In
another embodiment shown in FIG. 28, two elongated tubes 256 are
rotated and adjusted so that the injection ports 252 are oriented
to face each other. As shown in FIG. 28, gases exiting the
injection ports 252 impinge each other and mix in the bulging
section 284 prior to flowing across the surface of each substrate
242. In a further embodiment shown in FIG. 29, two elongated tubes
256 are rotated and adjusted so that the injection ports 252 are
oriented to face the center of the substrate 242.
[0123] The following examples are provided to further illustrate
the present invention and are not intended to limit the scope of
the invention in any way.
EXAMPLE 1
[0124] This example illustrates deposition of silicon nitride using
dichlorosilane (DCS) and NH.sub.3 gases. The deposition is
performed in a thermal processing apparatus including an injection
system of the present invention. The injection system comprises a
first injection tubes for introducing DCS gas and a second
injection tube for introducing NH.sub.3 gas. Each of the first and
second injection tubes is provided with a plurality of ports or
orifices for directing gas flow across the surface of each
substrate.
[0125] In one variation, the elongated tubes are rotated and
adjusted so that the injection ports are oriented to face the inner
surface of the liner. DCS and NH.sub.3 gases exiting the injection
ports away from wafers and impinge the liner inner surface prior to
flowing across the surface of each substrate.
[0126] In another variation, the elongated tubes are rotated and
adjusted so that the injection ports are oriented to face the
center of the substrate. DCS and NH.sub.3 gases exit the injection
ports and flow across the surface of each substrate.
[0127] FIG. 30 is a Computational Fluid Dynamics (CFD)
demonstration showing a uniform flow of DCS and NH.sub.3 gases
across the surface of the substrate in an injector configuration
where the injection ports are oriented toward the center of the
substrate, creating radially-inward flow of the gases. In this
case, the mass difference between DCS and NH.sub.3 is relatively
less (DCS=101, NH.sub.3=17), thus the gas velocities are more
similar.
EXAMPLE 2
[0128] This example illustrates deposition of silicon nitride using
bis tertiarybutylamino silane (BTBAS) and NH.sub.3 gases. The
deposition is performed in a thermal processing apparatus including
an injection system of the present invention. The injection system
comprises a first injection tube for introducing BTBAS gas and a
second injection tube for introducing NH.sub.3 gas. Each of the
first and second injection tubes is provided with a plurality of
ports or orifices for directing gas flow across the surface of each
substrate.
[0129] In one variation, the elongated tubes are rotated and
adjusted so that the injection ports are oriented to face the inner
surface of the liner. BTBAS and NH.sub.3 gases exiting the
injection ports away from wafers and impinge the liner wall prior
to flowing across the surface of each substrate.
[0130] In another variation, the elongated tubes are rotated and
adjusted so that the injection ports are oriented to face each
other. BTBAS and NH.sub.3 gases exit the injection ports and
impinge and mix prior to flowing across the surface of each
substrate.
[0131] FIG. 31 is a CFD demonstration showing a uniform flow of
BTBAS and NH.sub.3 gases across the surface of the substrate in an
injector configuration where the injection ports are oriented to
face each other, creating converging flow of the gases. In this
case, the molecular weight of BTBAS is 174, the molecular weight of
NH.sub.3 is 17. The recoil and mixing of BTBAS and NH.sub.3 ensure
a uniform gas velocity as the gases flow across the wafer and
results in exceptional within wafer uniformity of <1.5% (1
sigma) on a 300 mm wafer.
EXAMPLE 3
[0132] This example illustrates deposition of aluminum oxide
(Al.sub.2O.sub.3) using trimethyl aluminum (TMA) and ozone
(O.sub.3) gases. The deposition is performed in a thermal
processing apparatus including an injection system of the present
invention. The injection system comprises a first injection tube
for introducing TMA gas and a second injection tube for introducing
O.sub.3 gas. Each of the first and second injection tubes is
provided with a plurality of ports or orifices for directing gas
flow across the surface of each substrate.
[0133] In one variation, the elongated tubes are rotated and
adjusted so that the injection ports are oriented to face the inner
surface of the liner. TMA and O.sub.3 gases exiting the injection
ports away from wafers and impinge the liner wall prior to flowing
across the surface of each substrate.
[0134] In one variation, the elongated tubes are rotated and
adjusted so that the injection ports are oriented to face each
other. TMA and O.sub.3 gases exit the injection ports and impinge
and mix prior to flowing across the surface of each substrate.
[0135] FIG. 32 is a CFD demonstration showing a uniform flow of TMA
and O.sub.3 gases across the surface of the substrate in an
injector configuration where the injection ports are oriented to
face the liner wall, creating radially outward flow of the gases.
The recoil and mixing of TMA and O.sub.3 ensure a uniform gas
velocity as the gases flow across the surface of each wafer.
[0136] The foregoing description of specific embodiments and
examples of the invention have been presented for the purpose of
illustration and description, and although the invention has been
described and illustrated by certain of the preceding examples, it
is not to be construed as being limited thereby. They are not
intended to be exhaustive or to limit the invention to the precise
forms disclosed, and many modifications, improvements and
variations within the scope of the invention are possible in light
of the above teaching. It is intended that the scope of the
invention encompass the generic area as herein disclosed, and by
the claims appended hereto and their equivalents.
* * * * *