U.S. patent application number 12/013355 was filed with the patent office on 2009-07-16 for apparatus and method of aligning and positioning a cold substrate on a hot surface.
Invention is credited to Blake Koelmel, Alexander N. Lerner, Kai Ma, Abhilash J. Mayur.
Application Number | 20090181553 12/013355 |
Document ID | / |
Family ID | 40851027 |
Filed Date | 2009-07-16 |
United States Patent
Application |
20090181553 |
Kind Code |
A1 |
Koelmel; Blake ; et
al. |
July 16, 2009 |
APPARATUS AND METHOD OF ALIGNING AND POSITIONING A COLD SUBSTRATE
ON A HOT SURFACE
Abstract
Embodiments of the invention contemplate a method, apparatus and
system that are used to support and position a substrate on a
surface that is at a different temperature than the initial, or
incoming, substrate temperature. Embodiments of the invention may
also include a method of controlling the transfer of heat between a
substrate and substrate support positioned in a processing chamber.
The apparatus and methods described herein generally may also
provide an inexpensive and simple way of accurately positioning a
substrate on a substrate support that is positioned in a
semiconductor processing chamber. Substrate processing chambers
that can benefit from the various embodiments described herein
include, but are not limited to RTP, CVD, PVD, ALD, plasma etching,
and/or laser annealing chambers.
Inventors: |
Koelmel; Blake; (Palo Alto,
CA) ; Mayur; Abhilash J.; (Salinas, CA) ; Ma;
Kai; (Palo Alto, CA) ; Lerner; Alexander N.;
(San Jose, CA) |
Correspondence
Address: |
PATTERSON & SHERIDAN, LLP - - APPM/TX
3040 POST OAK BOULEVARD, SUITE 1500
HOUSTON
TX
77056
US
|
Family ID: |
40851027 |
Appl. No.: |
12/013355 |
Filed: |
January 11, 2008 |
Current U.S.
Class: |
438/799 ;
250/492.2; 257/E21.333; 257/E21.347 |
Current CPC
Class: |
C23C 16/4586 20130101;
H01L 21/67248 20130101; H01L 21/68742 20130101 |
Class at
Publication: |
438/799 ;
250/492.2; 257/E21.333; 257/E21.347 |
International
Class: |
H01L 21/268 20060101
H01L021/268 |
Claims
1. A processing chamber for processing a substrate, comprising: a
substrate support having a substrate supporting surface that is
disposed at an angle relative to the horizontal and a plurality of
ports which are adapted to direct a fluid to a region formed
between the substrate supporting surface and a substrate that is
disposed over the substrate supporting surface; a heating element
that is in thermal communication with the substrate supporting
surface and is adapted to heat the substrate disposed on the
substrate supporting surface; and two or more alignment features
having a substrate contact surface, wherein the two or more
alignment features are positioned to align the substrate relative
to the substrate supporting surface when the substrate is disposed
against the substrate contact surface of each of the two or more
alignment features.
2. The processing chamber of claim 1, wherein the heating element
is adapted to heat the substrate disposed on the substrate
supporting surface to a temperature greater than about 450.degree.
C.
3. The processing chamber of claim 1, further comprising: an
optical radiation assembly comprising an electromagnetic radiation
source and optics; and a translation mechanism that is adapted to
move the optics relative to the substrate support.
4. The processing chamber of claim 1, wherein the angle is less
than about 1 degree relative to the horizontal plane.
5. The processing chamber of claim 1, further comprising: one or
more walls that enclose a processing region; an exhaust system that
is adapted to reduce the pressure in the processing region to a
pressure below atmospheric pressure.
6. The processing chamber of claim 1, wherein the two or more
alignment features are pins that attached to the substrate
support.
7. A method of processing a substrate, comprising: heating
substrate support having a substrate supporting surface; delivering
a flow of a fluid to a plurality of ports formed in the substrate
support, wherein the flow of fluid creates a cushion of fluid that
is adapted to support the weight of the substrate; positioning a
substrate on the cushion of fluid for a desired period of time,
wherein the substrate is not in physical contact with the substrate
supporting surface; reducing the flow of fluid to allow the
substrate to contact at least a portion of the substrate supporting
surface; and performing a substrate processing step on the
substrate disposed on the substrate supporting surface.
8. The method of claim 7, wherein the substrate is in physical
contact with two or more alignment pins that are connected to the
substrate support.
9. The method of claim 7, wherein the flow of a fluid is between
about 200 sccm and about 6 slm.
10. The method of claim 7, wherein the processing step is a laser
annealing thermal process.
11. The method of claim 7, wherein the substrate is heated to a
temperature greater than about 450.degree. C.
12. The method of claim 7, further comprising positioning the
substrate supporting surface at an angle relative to the horizontal
before positioning the substrate on the cushion of fluid.
13. A method of processing a substrate, comprising: heating
substrate support having a substrate supporting surface; delivering
a flow of a fluid to a plurality of ports formed in the substrate
support, wherein the flow of fluid creates a cushion of fluid that
is adapted to support the weight of the substrate; positioning a
substrate on the cushion of fluid; aligning the substrate to the
substrate support while the substrate is positioned on the cushion
of fluid; reducing the flow of fluid to allow the substrate to
contact at least a portion of the substrate supporting surface; and
performing a substrate processing step on the substrate disposed on
the substrate supporting surface.
14. The method of claim 13, further comprising positioning the
substrate supporting surface at an angle relative to the horizontal
before positioning the substrate on the cushion of fluid.
15. The method of claim 13, wherein aligning the substrate to the
substrate support comprises waiting a desired period of time to
allow the substrate disposed on the cushion of fluid to come in
contact with two or more alignment features that are coupled to the
substrate support.
16. The method of claim 13, further comprising holding the
substrate on the cushion of fluid for a period of time longer than
the time required to align the substrate to the support.
17. The method of claim 13, wherein the substrate is not in
physical contact with the substrate supporting surface when the
substrate is positioned on the cushion of fluid.
18. The method of claim 17, wherein the substrate is in physical
contact with two or more alignment pins that are connected to the
substrate support.
19. The method of claim 13, wherein the flow of a fluid is between
about 200 sccm and about 6 slm.
20. The method of claim 13, wherein the processing step is a laser
annealing thermal process.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] Embodiments of the present invention generally relate to an
apparatus and method that is used to manufacture a semiconductor
device. More particularly, the invention is directed to an
apparatus and method that is used to thermally process a
substrate.
[0003] 2. Background of the Related Art
[0004] The integrated circuit (IC) market is continually demanding
greater memory capacity, faster switching speeds, and smaller
feature sizes. One of the major steps the industry has taken to
address these demands is to change from batch processing silicon
wafers in large furnaces to single wafer processing in a small
chamber.
[0005] During such single wafer processing the wafer is typically
heated to high temperatures so that various chemical and physical
reactions can take place in multiple IC devices defined in the
wafer. Of particular interest, favorable electrical performance of
the IC devices requires implanted regions to be annealed. Annealing
recreates a more crystalline structure from regions of the wafer
that were previously made amorphous, and activates dopants by
incorporating their atoms into the crystalline lattice of the
substrate, or wafer. Thermal processes, such as annealing, require
providing a relatively large amount of thermal energy to the wafer
in a short amount of time, and thereafter rapidly cooling the wafer
to terminate the thermal process. Examples of thermal processes
currently in use include Rapid Thermal Processing (RTP) and impulse
(spike) annealing. While such processes are widely used, current
technology is not ideal. It tends to ramp the temperature of the
wafer too slowly and expose the wafer to elevated temperatures for
too long. These problems become more severe with increasing wafer
sizes, increasing switching speeds, and/or decreasing feature
sizes.
[0006] In general, these thermal processes heat the substrates
under controlled conditions according to a predetermined thermal
recipe. These thermal recipes fundamentally consist of a
temperature that the semiconductor substrate must be heated to the
rate of change of temperature, i.e., the temperature ramp-up and
ramp-down rates and the time that the thermal processing system
remains at a particular temperature. For example, thermal recipes
may require the substrate to be heated from room temperature to
distinct temperatures of 1200.degree. C. or more, for processing
times at each distinct temperature ranging up to 60 seconds, or
more.
[0007] Moreover, to meet certain objectives, such as minimal
inter-diffusion of materials between different regions of a
semiconductor substrate, the amount of time that each semiconductor
substrate is subjected to high temperatures must be restricted. To
accomplish this, the temperature ramp rates, both up and down, are
preferably high. In other words, it is desirable to be able to
adjust the temperature of the substrate from a low to a high
temperature, or visa versa, in as short a time as possible.
[0008] The requirement for high temperature ramp rates led to the
development of Rapid Thermal Processing (RTP), where typical
temperature ramp-up rates range from 200 to 400.degree. C./s, as
compared to 5-15.degree. C./minute for conventional furnaces.
Typical ramp-down rates are in the range of 80-150.degree. C./s. A
drawback of RTP is that it heats the entire wafer even though the
IC devices reside only in the top few microns of the silicon wafer.
This limits how fast one can heat up and cool down the wafer.
Moreover, once the entire wafer is at an elevated temperature, heat
can only dissipate into the surrounding space or structures. As a
result, today's state of the art RTP systems struggle to achieve a
400.degree. C./s ramp-up rate and a 150.degree. C./s ramp-down
rate.
[0009] To resolve some of the problems raised in conventional RTP
type processes various scanning laser anneal techniques have been
used to anneal the surface(s) of the substrate. In general, these
techniques deliver a constant energy flux to a small region on the
surface of the substrate while the substrate is translated, or
scanned, relative to the energy delivered to the small region. The
scanned laser anneal, RTP and other thermal processes, which may
include pulsed laser anneal techniques, are commonly performed to
thermal process the devices formed on the surface of the
substrate.
[0010] To help reduce the processing time and improve the
performance of a thermal process performed in a thermal processing
chamber it is common to preheat the substrate to a moderate
temperature to improve throughput, reduce the induced thermal
stress, and improve the process results by reducing the temperature
range that the substrate needs go through during the thermal
process. Typically, the preheat temperature used in RTP and laser
annealing processes range from about 450.degree. C. to about
700.degree. C. In most cases, the preheat processes are performed
by positioning a substrate on a heated substrate support, which is
heated by embedded resistive heating elements positioned in the
substrate support, or is heated by lamps. One problem that arises
in the heated substrate support configuration is that when not all
regions of the substrate come into good thermal contact with the
heated substrate support at the same time, the substrate will
deform due to the varying thermal expansion of the substrate
created by the varying temperatures within the substrate. It has
been found that in cases where the center of a substrate comes in
contact with the support first, the substrate will deform into a
shape (e.g., concave shape) that can greatly affect process results
achieved from the center to edge of the substrate. In view of the
above, there is a need for an apparatus and method of receiving a
cold wafer on a heated support so that the thermal variation across
the substrate during the initial exposure to a heated substrate
support will not affect the process results.
[0011] Another issue that arises is that as device sizes decrease
the tolerance to temperature variation across the substrate has
become very low, such that the alignment and positioning of a
substrate relative to the substrate support can have an affect on
the uniformity of the process results achieved on the substrate.
Due to thermal uniformity and/or substrate breakage concerns it is
common in some thermal processing configurations to use a shadow
ring to shadow and/or retain a portion of the edge of the
substrate. Typically, since most semiconductor manufacturers are
concerned about the process results across the substrate surface
except a 3 mm (.about.0.12 inches) region at the edge of the
substrate, this is the only area over which the shadow ring can
cover to reduce thermal effects created at the edge of the
substrate. However, it is typical for most conventional automated
systems for the robot to have a positioning error of about
.+-.0.010 inches. Thermal uniformity results are generally affected
by substrate misplacements on the order of about 0.004 inches. To
resolve these types of issues a highly accurate or precise robots
are often required to precisely place a substrate within a desired
position in the processing chamber. These types of solutions are
often expensive and are not reliable due to variations in placement
due to wear on the robot, or temperature variations in the robot
assembly found after the transferring the first versus the
25.sup.th wafer in a process sequence. The complexity and cost of
the system also generally increase as the need for high temperature
robotic components (e.g., bearings), precise and expensive motors,
complex control systems, and reliable rotating vacuum seals.
Therefore, there is a need for a simple, inexpensive, and reliable
method and apparatus for accurately positioning and aligning the
substrate to the various chamber components.
SUMMARY OF THE INVENTION
[0012] The present invention generally provides a processing
chamber for processing a substrate, comprising a substrate support
having a substrate supporting surface that is disposed at an angle
relative to the horizontal, a plurality of ports which are adapted
to direct a fluid to a region formed between the substrate
supporting surface and a substrate that is disposed over the
substrate supporting surface, a heating element that is in thermal
contact with the substrate supporting surface and is adapted to
heat the substrate disposed on the substrate supporting surface,
and two or more alignment features having a substrate contact
surface, wherein the two or more alignment features are positioned
to align the substrate relative to the substrate supporting surface
when the substrate is disposed against the substrate contact
surface of each of the two or more alignment features.
[0013] Embodiments of the invention further provide a method of
processing a substrate, comprising heating a substrate support
having a substrate supporting surface, delivering a flow of a fluid
to a plurality of ports formed in the substrate support, wherein
the flow of fluid creates a cushion of fluid that is adapted to
support the weight of the substrate; positioning a substrate on the
cushion of fluid for a desired period of time, wherein the
substrate is not in physical contact with the substrate supporting
surface, reducing the flow of fluid to allow the substrate to
contact at least a portion of the substrate supporting surface, and
performing a substrate processing step on the substrate disposed on
the substrate supporting surface.
[0014] Embodiments of the invention further provide a method of
processing a substrate, comprising heating substrate support having
a substrate supporting surface, delivering a flow of a fluid to a
plurality of ports formed in the substrate support, wherein the
flow of fluid creates a cushion of fluid that is adapted to support
the weight of the substrate, positioning a substrate on the cushion
of fluid, aligning the substrate to the substrate support while the
substrate is positioned on the cushion of fluid, reducing the flow
of fluid to allow the substrate to contact at least a portion of
the substrate supporting surface, and performing a substrate
processing step on the substrate disposed on the substrate
supporting surface.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] A more particular description of the invention, briefly
summarized above, may be had by reference to the embodiments
thereof that are illustrated in the appended drawings. It is to be
noted, however, that the appended drawings illustrate only typical
embodiments of this invention and are therefore not to be
considered limiting of its scope, for the invention may admit to
other equally effective embodiments.
[0016] FIG. 1 is a cross-sectional view of a processing chamber and
substrate support assembly according to one embodiment of the
invention;
[0017] FIG. 2A is a cross-sectional view of a thermal processing
chamber according to one embodiment of the invention;
[0018] FIG. 2B is a plan view of the thermal processing chamber
shown in FIG. 2A according to one embodiment of the invention;
[0019] FIG. 2C is a close up isometric cross-sectional view of a
portion of the thermal processing chamber shown in FIG. 2A
according to one embodiment of the invention;
[0020] FIG. 3 illustrates a processing sequence according to one
embodiment of the invention.
DETAILED DESCRIPTION
[0021] Embodiments of the invention contemplate a method, apparatus
and system that are used to support and position a substrate on a
surface that is at a different temperature than the initial, or
incoming, substrate temperature. Embodiments of the invention may
also include a method of controlling the transfer of heat between a
substrate and substrate support positioned in a processing chamber.
The apparatus and methods described herein generally may also
provide an inexpensive and simple way of accurately positioning a
substrate on a substrate support that is positioned in a
semiconductor processing chamber.
[0022] Substrate processing chambers that can benefit from the
various embodiments described herein include, but are not limited
to a rapid thermal processing (RTP) chamber, a chemical vapor
deposition (CVD) chamber, a physical vapor deposition (PVD)
chamber, atomic layer deposition (ALD) chamber, dry etching
chamber, and/or laser annealing chamber. Substrates that may be
processed using the methods, apparatus and system described herein
may include, but are not limited to 200 mm, 300 mm or larger single
crystal silicon (Si), multi-crystalline silicon, polycrystalline
silicon, germanium (Ge), silicon carbide (SiC), glass, gallium
arsenide (GaAs), cadmium telluride (CdTe), cadmium sulfide (CdS),
copper indium gallium selenide (CIGS), copper indium selenide
(CuInSe.sub.2), gallilium indium phosphide (GaInP.sub.2), as well
as heterojunction cells, such as GaInP/GaAs/Ge or ZnSe/GaAs/Ge
substrates. Preferrably, the substrates are circular, but could be
any other desirable shape. In one embodiment, the substrate is a
semiconductor substrate that has a plurality of semiconductor
devices formed on a processing surface, which is generally on the
opposing side of the substrate from the lower surface W.sub.1 (FIG.
1) of the substrate W.
[0023] Embodiments of the invention can provide a substrate support
that is able to support and position a substrate using a fluid that
is delivered from a plurality of ports formed in a substrate
support assembly 100 (FIG. 1). The delivery of the fluid to the
substrate surface allows the substrate to be easily moved by
gravity, or other applied forces, to a desired position on the
substrate support. Also, as device sizes shrink the tolerance for
particle contamination has dramatically decreased, thus it is
generally desirable to prevent the lower surface W.sub.1 of the
substrate W from sliding against the substrate support, while it is
being positioning on the substrate support. Typically, the fluid is
a gas, such as nitrogen, helium, argon, krypton, neon, hydrogen, or
combinations thereof, but in some applications could be a
liquid.
[0024] FIG. 1 is a schematic cross-sectional view that illustrates
a processing chamber 101 that contains one or more walls 102, a lid
103, a substrate lift assembly 140 and a substrate support assembly
100 that is disposed on a support 106 in the processing region 104
of the processing chamber 101. In general, the processing chamber
101 may be an RTP, CVD, PVD, ALD, dry etching, laser annealing
chamber, or other similar type of substrate processing chamber. The
substrate lift assembly 140 generally contains a plurality of lift
pins 142 and an actuator 141 (e.g., air cylinder, DC servo motor
and lead screw) that are adapted to transfer a substrate to and
from the substrate support 110, which is contained in the substrate
support assembly 100, and a substrate transferring device, such as
a robot.
[0025] The substrate support assembly 100 generally contains a
substrate support 110, a fluid delivery system 130, temperature
control assembly 150, and a system controller 120. In one
embodiment, as shown in FIG. 1, the substrate "W" is supported on
the fluid "B" delivered from the fluid delivery system 130 to the
ports 111 (only one shown) formed in the substrate support 110. In
this view a substrate W is supported above the substrate support
110 by the fluid delivered through port 111 so that a gap "G" is
formed between the substrate W and the substrate support 110. The
gap "G" created by the fluid B may be between about 1 .mu.m and
about 1000 .mu.m. Optionally, a sensor (not shown), such as an
optical sensor, may be positioned and configured to detect the
height so that the system controller 120 can adjust the fluid flow
through the ports 111 so that a desired height is achieved.
[0026] In one embodiment, the temperature control assembly 150
generally contains a heating element 151 that is in thermal contact
with the substrate support 110 and a temperature controller 152.
The heating element 151 can be a resistive heating element that is
embedded within the substrate support 110. In one embodiment, the
heating element is adapted to heat a substrate W that is placed in
thermal contact with the substrate support 110 to an elevated
temperature, such as between about 450.degree. C. and about
800.degree. C. The temperature controller 152 generally contains a
power source (not shown) and a temperature measurement device (not
shown) that are adapted to control the temperature of the substrate
support 110 using conventional means.
[0027] In one embodiment, the substrate support 110 can be formed
from a metal, ceramic, plastic, semiconductor or other material
used to support substrates during processing. In one embodiment,
the substrate support 110 is made of a metal, such as aluminum, and
stainless steel. In another embodiment, the substrate support 110
is made of a ceramic material, such as quartz, sapphire, silicon
carbide, alumina, zirconia, aluminum nitride, or boron nitride.
[0028] The fluid delivery system 130 generally contains one or more
fluid control components that are used to provide and control the
delivery of fluid to the ports 111 formed in the substrate support
110. In one embodiment, the fluid delivery system 130 contains one
or more fluid sources (e.g., fluid sources 133A-133B) that deliver
fluid to each of the ports 111 using a fluid controlling device
(e.g., fluid controlling devices 131A-131B). The fluid controlling
devices are adapted to control the flow, velocity and/or pressure
of the fluid delivered to the ports 111 by use of commands sent
from the system controller 120. In one embodiment, the fluid
controlling devices (e.g., reference numerals 131A-131B) are
conventional mass flow controllers (MFCs) that are in communication
with the system controller 120. In another embodiment, the fluid
controlling devices are a fixed orifice that is configured to
deliver desired flows at various known pressures. The control of
the substrate movement can also be affected by the type of fluids
(e.g., gasses, liquids) delivered by the one or more ports, and
thus the viscosity, atomic mass, pressure, and density need to be
taken into account. The selection of the fluid generally must also
take into account its affect on the process performed in the
processing region 104.
[0029] The system controller 120 is adapted to control the various
components used to complete the substrate support assembly 100 and
processing chamber 101. The system controller 120 is generally
designed to facilitate the control and automation of the overall
process chamber and typically includes a central processing unit
(CPU) (not shown), memory (not shown), and support circuits (or
I/O) (not shown). The CPU may be one of any form of computer
processors that are used in industrial settings for controlling
various system functions, chamber processes and support hardware
(e.g., detectors, robots, motors, fluid sources, etc.) and monitor
the processes (e.g., substrate support temperature, power supply
variables, chamber process time, I/O signals, etc.). The memory is
connected to the CPU, and may be one or more of a readily available
memory, such as random access memory (RAM), read only memory (ROM),
floppy disk, hard disk, or any other form of digital storage, local
or remote. Software instructions and data can be coded and stored
within the memory for instructing the CPU. The support circuits are
also connected to the CPU for supporting the processor in a
conventional manner. The support circuits may include cache, power
supplies, clock circuits, input/output circuitry, subsystems, and
the like.
[0030] A program (or computer instructions) readable by the system
controller 120 determines which tasks are performable on a
substrate. Preferably, the program is software readable by the
system controller 120 that includes code to perform tasks relating
to monitoring, execution and control of the movement, support,
and/or positioning of a substrate, along with the various process
recipe tasks and various chamber process recipe steps being
performed in the processing chamber 101. In one embodiment, the
system controller may use conventional PID control algorithms to
control the delivery of fluid to the ports to actively control the
support and position of the substrate.
[0031] Embodiments of the invention generally provide orienting the
one or more ports 111 so that the fluid flowing from or within the
ports 111 can support the substrate W so that it can be positioned
as needed. In one embodiment, as shown in FIGS. 1 and 2 the port
111 contains an aperture 112 that is oriented in a substantially
normal orientation to the lower surface W.sub.1 of the substrate W.
In this configuration the inlet flow B.sub.i passing through the
aperture 112 strikes the lower surface W.sub.1 of the substrate W
causing the fluid to flow in various directions, such as directions
B.sub.1, B.sub.2. When the flow and/or pressure of the inlet flow
B.sub.i delivered from the fluid delivery system 130 through the
aperture 112 is high enough a gap "G" is formed between the
substrate W and the substrate support 110. The fluid delivered
through the apertures 112 to form the gap "G", thus form a fluid
cushion, on which the substrate is supported. Due to the
perpendicular orientation of the aperture 112 to the lower surface
W.sub.1 of the substrate W the inlet flow B.sub.i will generally
tend to support the substrate and move the substrate in only a
vertical direction (i.e., Z-direction). It should be noted that the
size of gap "G" formed by the flowing fluid will depend on pressure
of the flowing fluid relative to the pressure in the processing
region 104 (FIG. 1), the weight of the substrate W, the angle of
the impinging fluid, the properties of the fluid, and the velocity
of the flowing fluid from the apertures 112. It is believed that by
adjusting the velocity, flow, and angle with which the fluid
interacts with the substrate surface the momentum exchange and
friction created between the fluid and the substrate can be used to
dynamically position, move, and/or rotated the substrate relative
to the substrate support 110. It has been found that flows in the
subsonic regime (e.g., Mach number<1) greatly improve the
coupling efficiency of the fluid to the substrate. Thus, it is
generally desirable to design the apertures, and also deliver
fluids to the nozzles at pressures that will cause the fluid to
exit the apertures at a subsonic velocity.
[0032] As noted above, one problem that arises when using a heated
substrate support to heat a substrate is that either due to bow of
the substrate caused by residual internals stress in the substrate
or thermal stress created by thermal variations in the substrate,
not all regions of the substrate come into good thermal contact
with the heated substrate support at the same time. The thermal
contact variation thus can cause the substrate to further deform
due to the varying thermal expansion of the substrate created by
the varying temperatures across the substrate. Most substrate
processing steps require a "soak period" during the preheat step,
which is used to allow the temperatures across the substrate to
equilibrate to a temperature that is within a desirable range, or
that allow all regions of the substrate to reach a desired
temperature before the substrate processing step(s) can start. In
cases where the focal length of the energy delivered to the
substrate surface is an issue, such as laser annealing processes,
the distortion of the substrate can also greatly affect the process
results. Therefore, in these types of processes long soak times are
often required to assure that the substrate has a minimal
distortion. In general, the distortion of the substrate due to
varying thermal contact will greatly increase the "soak" time and
the throughput of the substrate processing step(s). In one example,
it has been found that bringing a substrate to a 450.degree. C.
substrate support requires at least 30 seconds of soak time to
allow the substrate to reach a minimally distorted shape and have a
desired thermal uniformity to allow a laser annealing process to be
performed. In view of the above, there is a need for an apparatus
and method of receiving a cold wafer on a heated support so that
the thermal variation across the substrate during the initial
exposure to a heated substrate support will not affect the process
results and substrate throughput.
[0033] To resolve these issues, in one embodiment, it is desirable
to position the substrate on a cushion of fluid that is formed over
the substrate supporting surface for a desired period of time to
allow the substrate temperature to uniformly heat up to a desired
temperature before it is placed in contact with the heated
substrate support or other supporting components. It is believed
that the cushion of fluid will thermally isolate the heated
substrate support from the cooler substrate, due to the need to
conduct heat across the formed gap "G" (FIG. 1), which then allows
the higher thermal conductivity of the substrate versus the thermal
conductivity of the fluid in the formed fluid cushion to even out
the temperature variation across the substrate as it is heated to a
preheat temperature. Therefore, by minimizing the temperature
variation the across the substrate, the distortion of the substrate
will be minimized, which in most processing applications will
reduce the time required to preheat the substrate, while also
increasing the average temperature of the wafer. Due to particle
concerns, substrate distortion concerns, and over all process
result concerns it is desirable to assure that the lower surface
W.sub.1 of the substrate W is not in physical contact with the
substrate support surface and/or other hot chamber components
(e.g., shadow ring (discussed below)) during the preheat step.
[0034] In one embodiment, the preheat process generally occurs in
three steps. In the first step, a substrate that is positioned on
the lift pins 142 is then disposed on a fluid cushion created above
the heated substrate support surface 110A by a fluid flowing
through the plurality of ports 111 that are in fluid communication
with the substrate support surface 110A. In one embodiment, a flow
of gas at a flow rate between about 200 standard cubic
centimeters/minute (sccm) and about 3000 sccms is used to support
the substrate above the substrate support surface 110A. In one
embodiment, a flow of nitrogen gas at a flow rate between about 200
sccm and about 600 sccm is used to support the substrate. In one
embodiment, the fluid is a gas, such as nitrogen, helium, argon,
krypton, neon, hydrogen, or combinations thereof.
[0035] In some cases, it is desirable to choose a gas that has a
good thermal conductivity, such as helium (e.g., k=1.411 mW/cm-K at
273.2K), to increase the temperature ramp up rate of the substrate.
However, using higher conductivity gases, such as helium, can tend
to increase the temperature variation across the substrate, which
will then lead to greater temperature non-uniformity, greater
distortion of the substrate, and a longer than necessary preheat
time. Surprisingly, it has been found that using lower thermal
conductivity gases, such as nitrogen (e.g., k=0.237 mW/cm-K at
273.2K), can reduce the preheat time by providing a large enough
thermal resistance to allow a substrate, such as a single crystal
silicon wafer, to maintain a desirable thermal uniformity and
distortion during the preheat portion of a high temperature thermal
process. Typical, high temperature process may use a substrate
support that is maintained at a temperature between about
450.degree. C. and about 800.degree. C.
[0036] Also, in one embodiment, the flow of fluid delivered through
the ports 111 can be increased to a point where convective heat
transfer has an affect on the heat transfer and uniformity of the
substrate disposed on the cushion of fluid. It is believed that
flows greater than about 3 slm at pressures near atmospheric
pressure and temperatures between about 450-800.degree. C. are at a
point where convective heat transfer affects the heat transfer
process between the substrate and the substrate support
surface.
[0037] In the next step, the substrate is maintained on the fluid
cushion for a desired period of time, or until a desired average
temperature is achieved within the substrate. In one embodiment,
the preheat time is between 5 seconds and about 30 seconds. In one
example, a preheat time of about 10 seconds is required to heat a
300 mm silicon substrate to a temperature of about 640.degree. C.
with a substrate support temperature of about 720.degree. C. using
a flow rate of 200 sccm of nitrogen that is supplied to the ports
111.
[0038] Finally, the fluid flow through the ports is reduced or
shut-off so that the substrate can contact the substrate support
surface 110A and the rest of the process can be performed on the
substrate. In one embodiment, the substrate is then clamped, or
"chucked", to the substrate surface 110A by use of a convention
electrostatic chuck means, a vacuum chuck or a physical clamping
mechanism to improve the thermal coupling between the substrate and
the substrate support.
Thermal Processing Chamber
[0039] FIG. 2A is a side cross-sectional view of an apparatus 200
for thermally processing a semiconductor substrate, according to an
embodiment of the invention. For the practice of the invention, the
preferred thermal process is annealing and annealing will be
described throughout the remainder of the Figures. The apparatus
200 comprises an electromagnetic radiation source 202, a processing
chamber 250, system controller 221, and optics 220 disposed between
the electromagnetic radiation source 202 and the substrate support
252. In one embodiment, the substrate W is a substrate that has a
high thermal conductivity, such as a single crystal silicon
substrate, silicon on insulator (SOI), Silicon Germanium or alloys
thereof, or the like.
[0040] In one embodiment, the electromagnetic radiation source 202
is capable of emitting continuous waves or rays of electromagnetic
radiation, such as light. By continuous wave it is meant that the
radiation source is capable of emitting radiation continuously,
i.e., not a burst, pulse, or flash of light. Furthermore, as the
continuous wave electromagnetic radiation needs to be adsorbed at
or near the surface of the wafer, the continuous wave
electromagnetic radiation preferably has a wavelength between 190
nm and 950 nm. More preferably, it has a wavelength of 808 nm.
[0041] In one embodiment, the electromagnetic radiation source 202
is capable of emitting radiation continuously for at least 15
seconds. The electromagnetic radiation source 202 may also comprise
multiple laser diodes, each of which produces uniform and spatially
coherent light at the same wavelength. In yet another preferred
embodiment, the power of the laser diodes is in the range of 0.5 kW
to 50 kW. Suitable laser diodes are made by Spectra-Physics of
California, or by Cutting Edge Optronics, Inc. of St. Charles Mo.
An example of a method and apparatus of laser annealing a substrate
is further described in the commonly assigned U.S. Pat. No.
7,005,601, filed Mar. 18, 2002, which is incorporated by reference
herein.
[0042] In another embodiment, the electromagnetic radiation source
202 is adapted to deliver electromagnetic energy that is used to
perform the pulse laser anneal process. Typical sources of
electromagnetic energy include, but are not limited to an optical
radiation source, an electron beam source, and/or a microwave
energy source. In one embodiment, the electromagnetic radiation
source 202 is adapted to deliver energy at a wavelength less than
about 1064 nm to a primarily silicon containing substrate. In one
aspect of the invention it is desirable to use an Nd:YAG
(neodymium-doped yttrium aluminium garnet) laser that is adapted to
deliver energy at a wavelength between about 266 nm and about 1064
nm. An example of a method and apparatus of a pulsed laser
annealing a substrate is further described in the commonly assigned
U.S. patent application Ser. No. 11/888,433 [Docket No. 11251],
filed Jul. 31, 2007, which is incorporated by reference herein.
[0043] The optics 220 preferably comprise one or more collimators
206 to collimate radiation 204 from the electromagnetic radiation
source 202 in a direction perpendicular to the upper surface 224 of
the substrate W. This collimated radiation 208 is then focused by
at least one lens 209 into a line of radiation 222 at an upper
surface 224 of the substrate W. Lens 209 is any suitable lens, or
series of lenses, capable of focusing radiation into a desired
shape, such as a line. The lens 209 may be a cylindrical lens, one
or more concave lenses, convex lenses, plane mirrors, concave
mirrors, convex mirrors, refractive lenses, diffractive lenses,
Fresnel lenses, gradient index lenses, or the like.
[0044] The apparatus 200 also comprises a translation mechanism 218
configured to translate the line of radiation 222 and the substrate
support 252 relative to one another. In one embodiment, the
translation mechanism 218 is coupled to the electromagnetic
radiation source 202 and/or the optics 220 to move the
electromagnetic radiation source 202 and/or the optics 220 relative
to the substrate support 252. In another embodiment, the
translation mechanism 218 is coupled to the substrate support 252
to move the substrate support 252 relative to the electromagnetic
radiation source 202 and/or the optics 220. In yet another
embodiment, the translation mechanism 218 moves both the
electromagnetic radiation source 202 and/or the optics 220, and the
substrate support 252. Any suitable translation mechanism may be
used, such as a conveyor system, rack and pinion system, mechanical
actuator, or the like.
[0045] The translation mechanism 218 is preferably coupled to a
system controller 221 to control the scan speed at which the
substrate support 252 and the line of radiation 222 move relative
to one another. The system controller 221 is generally similar to
the system controller 120 discussed above. In addition, the
translation of the substrate support 252 and the line of radiation
222 relative to one another is preferably along a path
perpendicular to the line of radiation 222 and parallel to the
upper surface 224 of the substrate W. In a preferred embodiment,
the translation mechanism 218 moves at a constant speed.
Preferably, this constant speed is approximately 2 cm/s for a 35
micron wide line. In another embodiment, the translation of the
substrate support 252 and the line of radiation 222 relative to one
another is not along a path perpendicular to the line of radiation
222.
[0046] The processing chamber 250 generally contains a substrate
support 252 configured to receive a substrate W thereon, a lift
assembly 240, a transparent window 255, gas delivery system 270,
and a chamber 251. The transparent window 255 is typically made of
quartz, sapphire or other optically transparent material that
allows the energy delivered from the electromagnetic radiation
source 202 to pass there through and heat the upper surface 224 of
the substrate W without significant energy loss.
[0047] The gas delivery system 270 generally contains a gas source
271 and an exhaust system 272 that are in fluid communication with
the processing region 260 that is enclosed by the walls 251A of the
chamber 251 and the transparent window 255. The gas source 271 is
generally adapted to provide a flow of a gas, such as an inert gas
(e.g., argon, nitrogen) into the processing region 260 to prevent
the oxidation of the substrate surface when it is heated by the
energy delivered from the electromagnetic radiation source 202 or
heated by the heating elements 253. The exhaust system 272 is
generally adapted to remove the injected gas delivered from the gas
source, remove any volatile contaminants generated during thermal
processing, and/or evacuate the processing region 260 to a pressure
below atmospheric pressure by use of conventional mechanical rough
pump, roots blower, or other similar fluid removal device. In one
embodiment, the exhaust system 272 is adapted to evacuate the
processing region 260 to a pressure less than about 300 Torr.
[0048] The chamber 251 is generally constructed of materials that
can maintain a chamber pressure below atmospheric pressure, such as
about 300 Torr, and a substrate deposition temperature between
about 450.degree. C. and about 800.degree. C. In one embodiment,
the chamber 251 can be made from a metal, such as aluminum or
stainless steel that is water cooled. In one embodiment, the
chamber 251 is coupled to transfer chamber 249 of a conventional
cluster tool that contains a robot (not shown) that is adapted to
transfer a substrate to and from the processing region 260 of the
processing chamber 250 through an access port 251B. In one
configuration, the transfer chamber 249 can be isolated from the
processing region 260 of the processing chamber 250 by use of a
conventional slit valve (not shown), or gate valve, to prevent
contaminants from passing in either direction through the access
port 251B.
[0049] The lift assembly 240 generally contains a plurality of lift
pins 242 and an actuator 241 (e.g., air cylinder, DC servo motor
and lead screw) that are adapted to move relative to the substrate
support 252 so that a substrate W can be transferred to and from
the substrate support 252, and to and from a substrate transferring
device, such as a robot. As shown in FIG. 2A, the lift pins 242 are
in the "down" position so that the substrate W can be positioned on
the substrate supporting surface 254A of the substrate support
252.
[0050] The substrate support 252 is generally a platform capable of
supporting the substrate W, as explained below. In one embodiment,
the substrate support 252 includes a means for grasping the
substrate, such as a frictional, gravitational, mechanical, or
electrical system. Examples of suitable means for grasping include:
mechanical clamps, electrostatic chuck, vacuum chuck, or the like.
In one embodiment, the substrate support 252 contains a heating
element 253 that is in electrical communication with temperature
control assembly 230 and is in thermal contact with a substrate W
when it is disposed on the substrate support 252. The heating
element 253 can be a resistive heating element that is embedded
within the support 254 of the substrate support 252. In one
embodiment, the temperature control assembly 230 is adapted to
supply power to the heating element 253 so that the substrate W can
be heated to an elevated temperature, such as between about
450.degree. C. and about 800.degree. C. The temperature control
assembly 230 generally contains a power source (not shown) and a
temperature measurement device (not shown) that are adapted to
control and monitor the temperature of the substrate support 252
using conventional means.
[0051] The substrate support 252 generally contains a support 254,
a fluid delivery system 130 (discussed above), and a temperature
control assembly 230 that are in communication with the system
controller 221. In one embodiment, the substrate "W" can be
supported on the fluid "B" delivered from the fluid delivery system
130 to the ports 111 formed in the substrate supporting surface
254A of the support 254. During one or more steps during thermal
processing a substrate W can be supported on a cushion of gas above
the substrate supporting surface 254A due to the fluid delivered
through plenum 254B to the ports 111, so that a gap (FIG. 1) can be
formed. The gap created by the fluid B may be between about 1 .mu.m
and about 1000 .mu.m. In one embodiment, the support 254 can be
formed from a metal, ceramic, plastic, semiconductor or other
material used to support substrates during processing. In one
embodiment, the support 254 is made of a ceramic material, such as
quartz, sapphire, silicon carbide, alumina, zirconia, aluminum
nitride, or boron nitride.
[0052] The fluid delivery system 130, which discussed above,
generally contains one or more fluid control components that are
used to provide and control the delivery of fluid to the ports 111
formed in the support 254. The fluid controlling devices are
adapted to control the flow, velocity and/or pressure of the fluid
delivered to the ports 111 by use of commands sent from the system
controller 221. The fluid controlling devices can be conventional
mass flow controllers (MFCs) that are in communication with the
system controller 221, or a fixed orifice that is configured to
deliver desired flow at a known pressure. The control of the
substrate movement can also be affected by the type of fluids
(e.g., gasses) delivered by the one or more ports, and thus the
viscosity, atomic mass, pressure, and density need to be taken into
account. The selection of the fluid generally must also take into
account its affect on the process performed in the processing
region 260.
[0053] In one embodiment, of the processing chamber 250 a shadow
ring 256 is disposed over a portion of the substrate support 252
and a substrate W when it is positioned on the substrate supporting
surface 254A, as shown in FIG. 2A. The shadow ring 256 is generally
designed to shadow the edge of the substrate to reduce any thermal
uniformity edge effects and prevent substrate breakage as the line
of radiation 222 is swept across the surface of the substrate W.
The shadow ring 256 may be positioned relative to the substrate W
and/or substrate supporting surface 254A by use of a shadow ring
lift assembly (not shown) to allow the substrate to be transferred
between the substrate supporting surface 254A and a robot (not
shown) without interfering with the shadow ring 256. The shadow
ring may be made of material that has a desired thermal mass, a
desirable emissivity and absorption coefficient, and is able to
withstand the energy delivered by the electromagnetic radiation
source 202.
[0054] FIG. 2B is a plan view of the apparatus 200 shown in FIG. 2A
looking through the transparent window 255. In this view a
plurality of ports 111 are disposed across the surface of the
substrate supporting surface 254A to actively support a substrate
(not shown for clarity) thereon during one or more steps during
processing. In one embodiment, the support 254 contains between
about 3 and about 8 ports that are evenly spaced around the center
"C" of the substrate supporting surface 254A. Also, as shown, the
apparatus 200 may contain three lift pins 242 that are evenly
spaced around the center "C" of the substrate supporting surface
254A.
[0055] As noted above, one issue that arises in typical high
temperature thermal processes is that as device sizes decrease the
tolerance to temperature variation across the substrate has become
very low (e.g., <2.degree. C. at 1390.degree. C.) such that the
alignment and positioning of a substrate relative to the substrate
support can have an affect on the uniformity of the process results
achieved on the substrate. Embodiments of the invention may also
provide an apparatus and method of accurately positioning and
aligning a substrate to one or more features coupled to or formed
on the substrate support 252. As noted above, since the placement
accuracy of the robot may vary during the life of the various
robotic components and may vary due to its varying exposure to the
high temperature processing environment a method of reliably
placing a substrate is needed.
[0056] To resolve this problem, in one embodiment, as shown in
FIGS. 2B and 2C the substrate support 252 contains a plurality of
alignment features 210 that are used to accurately align and
position a substrate W to the substrate supporting surface 254A,
support 254, and/or shadow ring 256. FIG. 2C is a close-up
isometric cross-sectional view of the substrate support 252 and
processing chamber 250. In one configuration, two or more alignment
features 210 (FIG. 2B) are used to align and position a substrate W
to the substrate supporting surface 254A, support 254, and/or
shadow ring 256. In one embodiment, the alignment features 210 are
connected to the support 254 (FIG. 2C) so that a substrate W that
when a substrate is placed in contact with a surface 210A it is
accurately aligned with center of the substrate supporting surface
254A, support 254, and/or shadow ring 256. In one embodiment, the
alignment features 210 are attached, bonded or pressed into to the
surface of the support 254. In one embodiment the shadow ring is
also accurately aligned to the support 254 by use of an alignment
feature(s) (not shown) that are used to align the shadow ring 256
to the support 254.
[0057] FIG. 3 illustrate one embodiment of a series of method steps
300 that are used to align the substrate to the alignment features
210. To facilitate the discussion of the method steps 300 the
various hardware components illustrated in FIGS. 1 and 2A-2C will
be referenced. The method steps 300 start with step 302 in which a
substrate is inserted into the processing region 260 (FIG. 2A)
through the access port 251B using a robot (not shown) that is
positioned in the transfer chamber 249. In one embodiment, the
substrate may be positioned in the processing region 260 using a
conventional robot blade (not shown) that is attached to
conventional robotic device (e.g., SCARA robot).
[0058] In the next step, step 304, the substrate is removed from
the substrate transferring device (e.g., robot blade) that
positioned the substrate within the processing region 260. In one
embodiment, the lift pins 242 are moved by the actuator 241 upwards
to a position where the substrate is separated from a substrate
transferring device.
[0059] In the next step, step 306, the substrate positioning device
(e.g., robot blade) is removed from the processing chamber 250. In
one embodiment, the processing region 260 is then isolated from the
transfer chamber 249 by use of a slit valve (not shown).
[0060] In the next step, step 308, a flow of fluid is provided to
the ports 111 formed in the substrate supporting surface 254A by
use of the fluid delivery system 130. The flow of fluid delivered
to the ports 111 form a fluid cushion that can be used to support
the weight of the substrate that is disposed thereon. As device
semiconductor device sizes shrink the tolerance for particle
contamination has dramatically decreased, thus it is generally
desirable to prevent the lower surface W.sub.1 (FIG. 1) of the
substrate W from contacting the chamber components, such as the
substrate supporting surface 254A while the substrate is being
moved or aligned (e.g., step 312 below). In one embodiment, the
fluid is a gas, such as nitrogen, helium, argon, xenon, krypton or
other typical gas. In one embodiment, the fluid is nitrogen
(N.sub.2) gas.
[0061] In the next step, step 310, the substrate is positioned on
the fluid cushion formed by the flowing fluid provided by the ports
111. In one embodiment, the substrate is disposed on the fluid
cushion by lowering the lift pins 242 so that the substrate is
positioned on and supported by the fluid cushion. The flow of the
fluid required to support a substrate may depend on the weight of
the substrate, the velocity of the fluid delivered by the ports,
the orientation and spacing of the ports on the support surface,
and the type of fluid delivered through the ports. In one
embodiment, a flow of gas at a flow rate between about 2 standard
liters/minute (slm) and about 30 slm is used to support the
substrate. In one embodiment, a flow of nitrogen gas at a flow rate
between about 2 slm and about 6 slm is used to support the
substrate.
[0062] In the next step, step 312, the substrate is aligned
relative to the substrate supporting surface 254A, support 254,
and/or shadow ring 256 by use of a device or other mechanical
means. In one embodiment, one or more conventional mechanically
actuated centering elements can be used to align the substrate to
the substrate supporting surface 254A, support 254, and/or shadow
ring 256.
[0063] In another embodiment, the fluid cushion provides a near
frictionless support of substrate that allows gravitationally
induced forces to position the substrate. Referring to FIGS. 2B and
2C, in one embodiment, the substrate supporting surface 254A is
positioned at an angle "A" (FIG. 2C) relative to the horizontal so
that gravity can provide a force that tends to cause the substrate
W disposed on the fluid cushion to move to a position where it
comes in contact with the surface 210A (e.g., outer surface) of at
least two of the two or more alignment features 210. In one
configuration, the substrate supporting surface 254A is formed so
that a permanent angle "A" is created between the substrate
supporting surface 254A and the horizontal plane by the way the
support 254 is connected to the chamber 251. In one embodiment, as
shown in FIG. 2B, two alignment features 210 are disposed on the
support 254 so that when a slight tilt of the substrate supporting
surface 254A is created by tilting the processing chamber 250, the
substrate moves to a position where it contacts the two alignment
features 210. For example, in one configuration, if the two
alignment features are two pins that are positioned so that a line
created between the pins is parallel to the edge 251C of the
processing chamber 250 (e.g., parallel to the Y-direction), when
the center of the substrate W is placed to the left of the center
"C" of the substrate supporting surface 254A by the robot (not
shown) and the processing chamber 250 is tilted so that the edge
251D of the process chamber is higher than the edge 251C, gravity
will cause the substrate to move towards and align itself with the
surface 210A of the two alignment features 210. In one embodiment,
the substrate supporting surface 254A is tilted at an angle "A"
between about 0.02 degrees and about 85 degrees from the horizontal
plane "H". It has been found that due to the near frictionless
system created by the fluid cushion the angle can be as small as
<1 degree and still provide adequate force to reliably align the
substrate to the alignment features 210. In general, it is
desirable to assure that substrate supporting surface 254A and the
optics 220 are in line so that the focal point of the line of
radiation 222 will not vary across the substrate.
[0064] In one embodiment, during steps 310 and 312, the substrate
is maintained on the cushion of fluid for a desired period of time,
or until a desired average temperature is achieved within the
substrate to preheat the substrate, as discussed above in relation
to FIG. 1. In one embodiment, the sum of the time used to complete
steps 310 and 312 is between 5 seconds and about 30 seconds. In one
embodiment, it is desirable to position the substrate on a cushion
of fluid that is formed over the substrate supporting surface for a
desired period of time to allow the substrate temperature to
uniformly heat up to a desired temperature before it is placed in
contact with the heated substrate support or other supporting
components. In another embodiment, it is desirable to allow the
substrate to contact the alignment features 210 while it is
positioned on the cushion of fluid to allow the thermal environment
for each processed substrates to be repeatable. In one embodiment,
the alignment features 210 are formed to minimize the contact
between the substrate and the surface 210A and/or are made of a
material that has a high thermal resistance (e.g., ceramic
material) so that the contact between the alignment pins and the
substrate will not be a source for temperature non-uniformity.
[0065] In the next step, step 314, the substrate is disposed on the
substrate supporting surface 254A by reducing or halting the flow
of fluid through the ports 111. In one embodiment, the fluid flow
through the ports is halted so that the substrate can contact the
substrate supporting surface 254A and the rest of the process can
be performed on the substrate. In one embodiment, to improve
thermal contact between the substrate and the substrate support the
substrate is then clamped, or "chucked", to the substrate surface
254A by use of a convention electrostatic chuck means, a vacuum
chuck means, or a physical clamping mechanism. In some
configurations, it may further be desirable to deliver a low flow
of fluid to the backside of the "chucked" substrate and the
substrate supporting surface 254A to improve the thermal coupling
during the processing step(s) (i.e., step 316). Referring to FIG.
2A, in one embodiment, the fluid line 254C that is connected to the
fluid delivery system 130 and the ports 111 is also controllably
connected to a conventional vacuum generating device 254D (e.g.,
mechanical pump) to allow the substrate to be vacuum chucked to the
substrate surface 254A through the ports 111 during one or more
parts of step 314 and/or step 316.
[0066] In the next step, step 316, one or more processing steps are
performed on the substrate. In general, the processing chamber 250
may be adapted to perform one or more RTP, CVD, PVD, ALD, dry
etching, laser annealing, or other similar type of substrate
processing steps on the substrate disposed on the support 254.
[0067] In the next step, step 318, the substrate is then removed
from the substrate support 252, transferred to a robot using the
lift assembly 240, and then removed from the processing region 260
through the access port 251B using the robot.
[0068] While the foregoing is directed to the preferred embodiment
of the present invention, other and further embodiments of the
invention may be devised without departing from the basic scope
thereof. The scope of the invention is determined by the claims
that follow.
* * * * *