U.S. patent application number 11/040625 was filed with the patent office on 2006-07-27 for method and apparatus for on the fly positioning and continuous monitoring of a substrate in a chamber.
This patent application is currently assigned to Applied Materials, Inc.. Invention is credited to Satish Sundar.
Application Number | 20060167583 11/040625 |
Document ID | / |
Family ID | 36697972 |
Filed Date | 2006-07-27 |
United States Patent
Application |
20060167583 |
Kind Code |
A1 |
Sundar; Satish |
July 27, 2006 |
Method and apparatus for on the fly positioning and continuous
monitoring of a substrate in a chamber
Abstract
A method and apparatus for positioning a substrate in a
substrate processing chamber. The method includes placing the
substrate on a substrate transfer blade, moving the substrate
transfer blade to a first position located in a transfer chamber,
and capturing at least one image that includes at least a portion
of the substrate transfer blade and at least a portion of the
substrate. The method also includes processing the image to
determine a position of a predetermined portion of the substrate
transfer blade and a position of predetermined portion of the
substrate. The method further includes determining an offset
between the position of the predetermined portion of the substrate
transfer blade and the position of the predetermined portion of the
substrate, and moving the substrate transfer blade to a second
position located in the substrate processing chamber, wherein the
second position is adjusted to account for the offset.
Inventors: |
Sundar; Satish; (Milpitas,
CA) |
Correspondence
Address: |
APPLIED MATERIALS, INC.;Patent Counsel
Legal Affairs Department, M/S 2061
P.O. Box 450A
Santa Clara
CA
95052
US
|
Assignee: |
Applied Materials, Inc.
Santa Clara
CA
|
Family ID: |
36697972 |
Appl. No.: |
11/040625 |
Filed: |
January 22, 2005 |
Current U.S.
Class: |
700/218 ;
414/222.02; 414/222.04; 414/936 |
Current CPC
Class: |
H01L 21/68707 20130101;
H01L 21/681 20130101; Y10S 414/136 20130101 |
Class at
Publication: |
700/218 ;
414/222.02; 414/222.04; 414/936 |
International
Class: |
G06F 7/00 20060101
G06F007/00 |
Claims
1. A method of positioning a substrate in a substrate processing
chamber, the method comprising: placing the substrate on a
substrate transfer blade; moving the substrate transfer blade to a
first position located in a transfer chamber; capturing at least
one image that comprises at least a portion of the substrate
transfer blade and at least a portion of the substrate; and
processing the at least one image to determine a position of a
predetermined portion of the substrate transfer blade and a
position of predetermined portion of the substrate; determining an
offset between the position of the predetermined portion of the
substrate transfer blade and the position of the predetermined
portion of the substrate; moving the substrate transfer blade to a
second position located in the substrate processing chamber,
wherein the second position is adjusted to account for the
offset.
2. The method of claim 1 wherein the predetermined portion of the
substrate transfer blade is a center of the substrate transfer
blade.
3. The method of claim 1 wherein the predetermined portion of the
substrate is a center of the substrate.
4. The method of claim 3 wherein the substrate is a semiconductor
wafer.
5. The method of claim 1 wherein the second position is a position
in which the wafer is centered with respect to the substrate
transfer blade.
6. The method of claim 1 wherein the step of processing the at
least one image comprises the steps of: identifying at least one
fiducial mark; calculating a location of the predetermined portion
of the substrate transfer blade based on the location of the at
least one fiducial mark; identifying an outer edge of the
substrate; and calculating a location of the predetermined portion
of the substrate.
7. The method of claim 6 wherein the predetermined portion of the
substrate transfer blade is a center of the substrate transfer
blade and the predetermined portion of the substrate is a center of
the substrate.
8. The method of claim 7 wherein the at least one fiducial mark is
fabricated on a peripheral edge of the substrate transfer
blade.
9. The method of claim 8 wherein the at least one fiducial marks
are three fiducial marks located at a distance of less than 8 mm
from a peripheral edge of the substrate.
10. The method of claim 7 wherein the at least one fiducial mark is
a geometric shape characterized by an optical reflectivity greater
than a portion of the wafer transfer blade.
11. The method of claim 7 wherein the at least one fiducial mark is
a geometric shape characterized by an optical reflectivity less
than a portion of the wafer transfer blade.
12. An apparatus for positioning a substrate in a substrate
processing chamber, the apparatus comprising: a transfer blade
coupled to a robotic assembly and adapted to support a substrate;
an optical assembly adapted to capture an image comprising at least
a portion of the transfer blade and at least a portion of the
substrate; and a computational device programmed to calculate the
position of the substrate relative to the transfer blade.
13. The apparatus of claim 12 further comprising: a plurality of
fiducial marks associated with the transfer blade, wherein the
computational device utilizes the plurality of fiducial marks in
calculating the position of the substrate relative to the transfer
blade.
14. The apparatus of claim 13 wherein the plurality of fiducial
marks are fabricated on a peripheral edge of the transfer
blade.
15. The apparatus of claim 14 wherein the plurality of fiducial
marks are at least three fiducial marks located at a distance of
less than 8 mm from a peripheral edge of the substrate.
16. The apparatus of claim 12 wherein the substrate is a
semiconductor wafer.
17. A method for positioning a substrate in a substrate processing
chamber, the method comprising: providing a substrate support
disposed in the substrate processing chamber; providing a plurality
of fiducial marks disposed on at least one component of the
substrate processing chamber; placing a substrate on the substrate
support; capturing an image comprising at least one of the
plurality of fiducial marks disposed on the at least one component
of the substrate processing chamber and at least a portion of the
substrate; determining an offset between a predetermined position
of the substrate support and a predetermined position of the
substrate; and repositioning the substrate on the substrate support
in response to the offset.
18. The method of claim 17 wherein the plurality of fiducial marks
are structural features of the at least one component of the
substrate processing chamber.
19. The method of claim 17 wherein the fiducial marks are geometric
shapes located on the at least one component of the substrate
processing chamber.
20. A method for positioning a substrate in a substrate processing
chamber, the method comprising: providing a substrate support
disposed in the substrate processing chamber; providing a plurality
of fiducial marks disposed on the substrate support; placing a
substrate on the substrate support; capturing a first image
comprising at least one of the plurality of fiducial marks disposed
on the substrate support and at least a portion of the substrate;
determining an offset between a predetermined position of the
substrate support and a predetermined position of the substrate;
and repositioning the substrate on the substrate support in
response to the offset.
21. The method of claim 20 wherein the fiducial marks are geometric
patterns located on the substrate support.
22. The method of claim 21 further comprising: placing an
integrated calibration field on the substrate support; capturing a
calibration image comprising at least a portion of the integrated
calibration field; creating a mapping based on the calibration
image; and calibrating the first image based on the mapping.
23. An apparatus for positioning a substrate in a substrate
processing chamber, the apparatus comprising: a substrate support
disposed in the processing chamber; an optical system adapted to
capture an image comprising at least a portion of the substrate
support and a portion of a substrate supported by the substrate
support; a computational device adapted to calculate a position of
a predetermined portion of the substrate relative to the substrate
support; and a transfer blade adapted to reposition the substrate
in response to the calculation produced by the computational
device.
24. The apparatus of claim 23 further comprising: at least one
fiducial mark associated with the substrate support, wherein the
computational device utilizes the at least one fiducial mark in
calculating the position of the predetermined portion of the
substrate relative to the substrate support.
Description
BACKGROUND OF THE INVENTION
[0001] This present invention relates generally to semiconductor
manufacturing equipment. More specifically, the present invention
relates to controlling the position of a semiconductor substrate
during processing. Merely by way of example, the invention has been
applied to centering a semiconductor wafer inside a processing
chamber. The method and apparatus can be applied to other
applications as well such as positioning of disk drive substrates,
flat panel display substrates, mechanical substrates, and the
like.
[0002] The processing of semiconductor wafers to form integrated
circuits and the like generally requires a number of sequential
processing steps. Generally, these processes include steps to
create devices, conductors, and insulators on the substrate. Often,
these processes are performed in a number of processing chambers,
each chamber dedicated to a single process. Some semiconductor
processing systems utilize a central transfer chamber to couple
these dedicated processing chambers, forming a "cluster tool."
Examples of these cluster tools include the families of
PRODUCER.RTM., CENTURA.RTM., AND ENDURA.RTM. processing systems
available from Applied Materials, Inc., of Santa Clara, Calif.
[0003] Generally, a cluster tool includes a central transfer
chamber that houses a robot to facilitate transfer of the substrate
between the surrounding processing chambers. This central transfer
chamber is generally coupled to at least one load lock chamber and
one or more processing chambers. In some cluster tools, multiple
robots are located in the central transfer chamber to facilitate
the transfer of semiconductor wafers from the load lock chambers to
the processing chambers. Generally, semiconductor wafers are stored
in wafer cassettes and transferred to the central transfer chamber
via the load locks in preparation for processing. The processing
chambers are typically utilized to perform various processing steps
such as etching, physical vapor deposition, chemical vapor
deposition, ion implantation and the like. During wafer transfer
operations, semiconductor wafers are supported on moveable wafer
transfer blades.
[0004] In order to accurately place the semiconductor wafers in a
given processing chamber, control over the wafer handling and
transfer process is typically exercised by the cluster tool. As the
size of semiconductor device features has decreased, processing
tolerances have become more stringent and the accuracy requirements
for wafer handling have increased. For example, in some processing
steps, the placement tolerance for positioning the wafer in the
processing chamber has been reduced to smaller dimensions.
[0005] Accurate placement of the semiconductor wafers in the
processing chambers may be hindered by a variety of factors. For
example, thermal expansion of the components that make up the wafer
transfer blades may shift the position of the semiconductor wafer
from a desired position. Additionally, motion of the wafer transfer
blades may result in the semiconductor wafer sliding on the wafer
transfer blade during motion of the wafer transfer blade.
Consequently, the placement position of the semiconductor wafer
inside the processing chamber may be inaccurate.
[0006] Several methods and apparatus have been utilized to
determine the position of wafer transfer blades and other
components of a robotic transfer system. In one approach, the
position of a wafer is determined by measuring a reference position
of a robot utilized to transfer a wafer between chambers of a
semiconductor manufacturing system. However, although the position
of a robot and an associated wafer transfer blade may be accurately
determined, the position of a semiconductor wafer supported by such
a wafer transfer blade may be unknown. For example, although a
semiconductor wafer may be accurately positioned on a wafer
transfer blade at the location where the wafer is removed from the
wafer cassette, the wafer may slide during the movement of the
robotic assembly through the load lock and transfer chamber. In
fact, sliding of the wafer on the wafer transfer blade may cause
the wafer to become misaligned in an undetermined manner.
Therefore, in the general case, even though the position of the
robot or the wafer transfer blade may be accurately determined and
controlled, the position of the semiconductor wafer may be
undetermined.
[0007] In another approach, an optical emitter that produces a
collimated beam of light is disposed on the surface of a
transparent cover on the surface of the wafer transfer chamber.
Detectors also mounted on the surface of the chamber are tripped
when the beam of light is interrupted by either the wafer or the
wafer transfer blade. Thus, the system can determine the position
of the wafer with respect to the wafer transfer blade. Based on the
detected position, the system can correct for wafer position
errors. Sensor systems of the type known to be used in this
approach are generally accurate to .about.mils. As semiconductor
device dimensions have decreased, increased handling accuracy is
desirable, thus providing motivation for wafer handling apparatus
with increased accuracy.
[0008] Therefore, there is a need in the art for an improved method
and apparatus for positioning and continuously monitoring the
position of a semiconductor wafer in a processing chamber.
SUMMARY OF THE INVENTION
[0009] Embodiments in accordance with the present invention relate
generally to semiconductor processing systems. More particularly,
embodiments according to the present invention relate to the
measurement and control of the position of a semiconductor
substrate. In a specific embodiment according to the present
invention, a method of centering a semiconductor wafer in a
processing chamber is disclosed.
[0010] In one embodiment of the method of the present invention,
the method includes placing the substrate on a substrate transfer
blade, moving the substrate transfer blade to a first position
located in a transfer chamber, and capturing at least one image
that comprises at least a portion of the substrate transfer blade
and at least a portion of the substrate. The method also includes
processing the at least one image to determine a position of a
predetermined portion of the substrate transfer blade and a
position of predetermined portion of the substrate. The method
further includes determining an offset between the predetermined
portion of the substrate transfer blade and the predetermined
portion of the substrate, and moving the substrate transfer blade
to a second position located in the substrate processing chamber,
wherein the second position is adjusted to account for the
offset.
[0011] In an alternative embodiment according to the present
invention, the method includes providing a substrate support
disposed in the substrate processing chamber, providing a plurality
of fiducial marks associated with the substrate support, and
placing a substrate on the substrate support. The method also
includes capturing an image comprising at least one of the
plurality of fiducial marks disposed on the substrate support and
at least a portion of the substrate, and determining an offset
between a predetermined position of the substrate support and a
predetermined position of the substrate. The method also includes
repositioning the substrate on the substrate support in response to
the offset.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a simplified schematic illustration of a substrate
positioning apparatus according to an embodiment of the present
invention.
[0013] FIG. 2 is a simplified schematic illustration of a top view
of a substrate transfer blade according to an embodiment of the
present invention.
[0014] FIG. 3 is a simplified schematic illustration of a top view
of a substrate transfer blade according to an alternative
embodiment of the present invention.
[0015] FIG. 4 is a simplified perspective side view of a substrate
processing apparatus according to an embodiment of the present
invention.
[0016] FIG. 5 is a simplified schematic top view of a portion of a
transfer chamber according to an embodiment of the present
invention.
[0017] FIG. 6 is a simplified schematic illustration of a transfer
blade with an integrated calibration field according to an
alternative embodiment of the present invention.
[0018] FIG. 7 is a simplified flowchart of a method of positioning
a substrate in a substrate processing system in accordance with an
embodiment of the present invention.
[0019] FIG. 8 is a simplified schematic illustration of a portion
of a substrate processing system including a processing chamber
according to an embodiment of the present invention.
[0020] FIG. 9 is a simplified schematic illustration of a
perspective cut-away view of a substrate processing chamber and a
substrate support with an integrated calibration field according to
an embodiment of the present invention.
[0021] FIG. 10 is a simplified flowchart of a method of positioning
a substrate in a processing chamber in accordance with an
alternative embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0022] According to the present invention, semiconductor
manufacturing systems are provided. More particularly, the
invention provides methods and apparatus for controlling the
position of a semiconductor substrate during processing. Merely by
way of example, the invention has been applied to centering a
semiconductor wafer inside a processing chamber. The method and
apparatus can be applied to other applications as well such as
positioning of disk drive substrates, flat panel display
substrates, mechanical substrates, and the like.
[0023] FIG. 1 is a simplified schematic illustration of a substrate
positioning apparatus 105 according to an embodiment of the present
invention. Substrate transfer blade 120 is mechanically coupled to
transfer robot 110 with arms 112. Substrate 125 is supported by
arms 122 of the substrate transfer blade. In a particular
embodiment, the substrate is a semiconductor wafer. Rotation of the
robot's base 130 in direction 132 and movement of the robot's arm
in directions 134 enable the transfer blade to move in directions
140 and 142.
[0024] FIG. 2 is a simplified schematic illustration of top view of
a substrate transfer blade 120 according to an embodiment of the
present invention. The transfer blade can be made from any suitable
material. The suitable material generally has mechanical stability
and an ability to be machined accurately. The material should also
be compatible with other materials used herein, and be compatible
in a working environment. In one embodiment, the transfer blade is
made from aluminum, however this is not required by the present
invention. Other materials can also be used.
[0025] As illustrated in FIG. 2, a predetermined number of fiducial
marks 210 are located on the upper surface of the transfer blade.
In a specific embodiment, 12 fiducial marks are located on the
upper surface of the transfer blade. Alternative embodiments
utilize a larger or smaller number of fiducial marks.
[0026] In the embodiment illustrated in FIG. 2, the substrate is a
generally circular semiconductor wafer 125 illustrated as a dashed
circle. The wafer periphery abuts stops 220 and 222 attached to the
transfer blade. However, the claimed invention is not limited to
substrates in the form of semiconductor wafers. The present
invention provides a method and apparatus that is applicable to a
variety of substrates. For example, circular and rectangular glass
substrates used in the manufacturing of flat panel displays are
positioned and monitored in alternative embodiments. Moreover, disk
drives and generally shaped mechanical components and parts are
additional substrates for which the present invention is
applicable.
[0027] In an embodiment according to the present invention, the
fiducial marks are located at the periphery of the wafer transfer
blade, but this is not required. The fiducial marks are generally
distinctive and present an optical reflectance signature different
than selected portions of the wafer transfer blade. In one
embodiment, the fiducial marks are located a predetermined distance
from the outer edges of the substrate. For example, in a particular
embodiment, the fiducial marks are approximately 5-8 mm from the
outer edges of the substrate. In other embodiments, the fiducial
marks are a greater or lesser distance. In another specific
embodiment, the fiducial marks are located at positions where a
substrate that is displaced to the maximum extent allowable by the
application, does not obstruct the fiducial marks. In an
alternative embodiment, the fiducial marks are located a
predetermined distance from the edge of the transfer blade. For
instance, the fiducial marks are 5-8 mm from the edge of the
transfer blade in a specific alternative embodiment.
[0028] In a particular embodiment according to the present
invention, the fiducial marks are a series of circular features
formed by anodizing pre-selected circular portions of the wafer
transfer blade and subsequently removing the anodization. In an
alternative embodiment, anodization of a reverse image of the
circular fiducial marks followed by removal of the anodized regions
is employed to create the fiducial marks.
[0029] In yet another alternative embodiment, fiducial marks in the
form of alternating geometric patterns are formed on the wafer
transfer blade. FIG. 3 illustrates such an alternative embodiment
in which alternating crosses and squares are used as fiducial
marks.
[0030] FIG. 4 is a simplified perspective side view of a substrate
processing apparatus according to an embodiment of the present
invention. Substrate positioning apparatus 105, previously
described with reference to FIG. 1, is located in transfer chamber
410. Substrate processing chamber 420 is coupled to the transfer
chamber. A slit valve (not shown) is operable to open port 425 so
that the substrate 125 can be moved between the transfer chamber
and the processing chamber. Optical system 430 is mounted in
proximity to transparent window 435 located in the upper surface of
the transfer chamber. In this embodiment, the optical system is
arranged so that an image of objects present in the transfer
chamber is captured by the optical system. For example, the optical
system is arranged in one embodiment so that objects present in the
field of view 440 are captured by the optical system.
[0031] FIG. 5 is a simplified schematic top view of a portion of
the transfer chamber 410 from the perspective of the optical system
430 (not shown). In embodiments according to the present invention,
the optical system is calibrated as will be described below.
Additionally, the optical system is used to capture at least one
image through the window 435 located on the upper surface of the
transfer chamber. In the embodiment illustrated in FIG. 5, two
images are captured that include a portion of the substrate 125
along with fiducial marks 210 that are present on the transfer
blade 120. In the particular embodiment illustrated in FIG. 5, the
image contains a left field of view 520 and a right field of view
525.
[0032] Images of fields 520 and 525 are processed by computer
algorithms known to those of skill in the art to determine the
position of a predetermined portion of the transfer blade based on
the positions of the fiducial marks 210. Further analysis is
performed to determine the position of a predetermined portion of
the substrate based on the position of the two arcs 530 and 535
associated with the upper edge of the substrate in the two images,
respectively. In a particular embodiment, the predetermined portion
of the transfer blade is the center of the transfer blade and the
predetermined portion of the substrate is the center of the
substrate. Additionally, the offset between these positions is
determined and this information is utilized to control the transfer
blade in placing the substrate on a substrate support located
inside a processing chamber.
[0033] In embodiments according to the present invention, the
transfer blade is fabricated to known tolerances so that the
position of the fiducial marks relative to the geometry of the
transfer blade can be determined. For example, the distance from
various fiducial marks to the center of the transfer blade is
selected prior to manufacturing and can be verified after the
completion of manufacturing. Moreover, thermal expansion of the
transfer blade can be mapped during operation of the substrate
processing system by monitoring the positions of the fiducial
marks. For instance, expansion of the transfer blade will result in
an increase in the distance between fiducial marks on opposite
sides of the transfer blade. This increased distance can be
monitored to determine the thermal expansion characteristics of the
transfer blade and recalculate the position of the center of the
transfer blade.
[0034] In embodiments according to the present invention, the
calculated offset between the center of the transfer blade and the
center of the substrate is utilized during placement of the
substrate in the processing chamber. For example, given that the
position of the center of the transfer blade relative to the robot
arm is known, the substrate can be placed in a desired position in
the processing chamber by accounting for the offset between the
center of the substrate and the center of the transfer blade.
Merely by way of example, a semiconductor wafer could be centered
on a substrate support present in a processing chamber.
[0035] In alternative embodiments, a set of images that include the
top portion of the transfer blade and a set of images that include
the bottom portion of the transfer blade are captured. These two
sets of images are captured sequentially at locations 520 and 530
as illustrated in FIG. 5. The first set of images is captured as
the upper portions of the transfer blade and substrate pass below
the transparent window 435 illustrated in FIGS. 4 and 5. As the
robot moves the transfer blade in direction 540, the second set of
images is captured as the lower portions of the transfer blade and
substrate (not shown) pass below the transparent window. Computer
analysis is performed to determine the center of the transfer blade
and the substrate based on the four images included in these two
sets of images. Adjustment of the substrate placement position in
the processing chamber is accomplished as described above.
[0036] In embodiments according to the present invention, a single
video camera with a CCD array is disposed above the transparent
window fabricated in the upper surface of the transfer chamber. The
transparent window may be made of any suitable material. The
suitable material generally possesses a degree of optical
transparency and uniformity acceptable for applications of the
present invention. Generally, the optical properties of the window
are invariant with time and temperature. In an embodiment according
to the present invention, the transparent window is made from
plexiglass, however this is not required by the present invention.
Other materials can also be used. In this embodiment, the video
camera is positioned to image at least one location inside the
transfer chamber. Merely by way of example, an embodiment according
to the present invention positions the camera to image an area
2''.times.2'' in size at a location approximately 5 cm below the
transparent surface.
[0037] The camera used in an embodiment according to the present
invention operates over a predetermined wavelength region and at a
predetermined spatial resolution sufficient to capture at least one
image that includes a portion of the transfer blade and a portion
of the substrate. In a specific embodiment according to the present
invention, a camera operating in the visible region of the
electromagnetic spectrum with a predetermined pixel size is
utilized. Merely by way of example, an embodiment according to the
present invention uses a Sony XC-003 1/3'' 3 CCD color camera, with
a resolution of 768 (H).times.494 (V), available from Sony
Electronics, Inc., Sony Business Solutions & Systems Company
(BSSC), San Jose, Calif.
[0038] In one embodiment, video cameras operating in the visible
region of the electromagnetic spectrum are utilized. Visible
optical radiation present in the semiconductor manufacturing
facility provides illumination for the optical video cameras. In an
alternative embodiment, optical radiation in the infrared region of
the spectrum is used to illuminate the fiducial marks. Accordingly,
in this alternative embodiment, video cameras sensitive to infrared
radiation are utilized. In yet another alternative embodiment, an
ultraviolet radiation source and corresponding camera is used. The
shorter wavelength radiation provided by the ultraviolet source
results in a reduction in the diffraction limit achievable with the
imaging system. In another alternative embodiment, the radiation
source is a combination of ultraviolet, visible, and infrared
sources. In this alternative embodiment, appropriate cameras
matched to the illumination source are utilized.
[0039] The optical system utilized in embodiments according to the
present invention is generally calibrated to compensate for optical
properties of the transparent window along with other optical
system components. For example, the index of refraction associated
with the transparent window may vary as a function of position.
Additionally, the thickness of the window may vary as a function of
position. Accordingly, embodiments according to the present
invention utilize a calibration step to compensate for variations
in the optical properties of the transparent window.
[0040] In a specific embodiment, a substrate featuring a
calibration pattern is supported on the transfer blade, which is
moved to a location below the transparent window in the transfer
chamber. In this specific embodiment, an image is captured of the
calibration pattern present on the substrate and processed by
computer algorithms to calibrate the camera system. In an
alternative embodiment, a series of images are captured of the
calibration pattern as the transfer blade is translated through the
transfer chamber. For example, the transfer blade can be translated
in direction 540 as illustrated in FIG. 5. This series of images is
utilized to calibrate the system and to account for variations in
the optical system of a smaller or larger scale than that of the
calibration field.
[0041] Recalibration of the optical system can be performed as
desired. In an embodiment according to the present invention,
recalibration is performed after the transfer chamber lid is
opened, accidental or deliberate movement of the camera system, or
the like. In yet another alternative embodiment, calibration of the
optical system is performed by utilizing a calibration field
disposed on the transfer blade. FIG. 6 is a simplified schematic
illustration of a transfer blade with an integrated calibration
field according to an alternative embodiment of the present
invention. In this alternative embodiment, the transfer blade is
fabricated to include an integrated calibration field on a portion
of the transfer blade, the view of which is not obstructed by the
substrate. For example, in FIG. 6, the integrated calibration field
610 is located on the transfer blade 120 at a position horizontally
displaced in direction 620 from the substrate 125. The optical
system captures images of the fiducial marks 210 and the substrate
in the manner described above. Additionally, the imaging system
captures at least one image of the calibration field for use in
system calibration. Multiple images of the calibration field are
captured as the transfer blade is moved in yet another alternative
embodiment according to the present invention. The multiple images
are utilized to account for variations in the optical system of a
larger or smaller scale than that of the calibration field. These
multiple images are captured as the wafer transfer blade moves
through various positions in the transfer chamber.
[0042] As mentioned previously, the thermal expansion of the
transfer blade can be mapped during operation by monitoring the
relative positions of the fiducial marks. This monitoring may be
performed in real time to determine the effects of thermal
expansion on the robotic assembly and the transfer blade. Data
related to thermal expansion and contraction of the mechanical
assemblies may be used in selecting the placement location of the
substrate inside the processing chamber.
[0043] FIG. 7 is a simplified flowchart of a method of positioning
a substrate in a substrate processing system in accordance with an
embodiment of the present invention. First, a substrate is
transferred from the load lock chamber to the central transfer
chamber. The optical imaging system is calibrated to account for
any variations in the optical uniformity of the imaging system.
Next, at least one image is captured that includes at least a
portion of the transfer blade and at least a portion of the
substrate. The captured image is processed using computer
algorithms to determine the position of a predetermined portion of
the transfer blade. In one embodiment, the predetermined portion of
the transfer blade is the center of the transfer blade.
Additionally, the captured image is processed using computer
algorithms to determine the position of a predetermined portion of
the substrate. In one embodiment, the predetermined portion of the
substrate is the center of the substrate. An offset between the two
positions is calculated in the next step. Finally, the transfer
blade is moved to a location in the processing chamber. The
location is selected to account for the offset previously
determined. Thus, the substrate is placed in the processing chamber
with increased accuracy.
[0044] In an alternative embodiment according to the present
invention, the substrate position is determined and adjustments to
the substrate position are made after the substrate is transferred
to the processing chamber. FIG. 8 is a simplified schematic
illustration of a portion of a substrate processing system
including processing chamber 420. Merely by way of example, a
processing chamber suitable for use with the Endura.RTM. processing
system, manufactured by Applied Materials, of Santa Clara, Calif.
is an example of such a processing chamber. However, the present
invention is not limited to a particular substrate processing
system. Substrate 125, supported on transfer blade 120, is
introduced into the processing chamber through port 425 and placed
on substrate support 810 by transfer robot 110. Process gases are
introduced into the chamber from gas source 820. Chamber
temperature is controlled by a heater assembly (not shown).
Additional components of the processing chamber are omitted for
sake of clarity.
[0045] Embodiments as illustrated in FIG. 8 capture at least one
image of the substrate after it is placed on the substrate support
in the processing chamber. The image includes at least a portion of
the substrate and a portion of the components of the processing
chamber disposed inside the chamber. For example, in a particular
embodiment, the image includes at least a portion of the substrate
support. Merely by way of example, specific parts of the substrate
support are imaged and used as reference points in determining the
relative position of the substrate to the substrate support. For
instance, one embodiment according to the present invention
captures an image that includes the outer edge of the susceptor or
heater. An alternative embodiment captures an image that includes
any contrasting marks present on the substrate support, including,
but not limited to holes for lift pins and the like. In another
embodiment, other components of the processing chamber are utilized
as reference points in determining the relative position of the
substrate to the substrate support.
[0046] The image is processed by computer algorithms known to those
of skill in the art to determine the position of a predetermined
portion of the components of the processing chamber disposed inside
the chamber. Additionally, the image is processed to determine the
offset between this position and a predetermined portion of the
substrate. In one embodiment, the predetermined portion of the
components of the processing chamber disposed inside the chamber is
the center of the substrate support and the predetermined portion
of the substrate is the center of the substrate. Utilizing the
relative offset between the positions of the substrate and the
substrate support, the substrate is repositioned at the desired
position in the processing chamber by use of the transfer robot. In
a specific embodiment, the substrate is repositioned so that it is
centered on the substrate support within a predetermined tolerance.
For example, in a particular embodiment according to the present
invention, the substrate is centered with a tolerance of less than
or equal to 1 mil.
[0047] In alternative embodiments, particular fiducial marks are
placed on the substrate support and utilized to determine the
position of the substrate support with respect to the substrate. In
embodiments that utilize components of the processing chamber as
reference points as well as embodiments that utilize particular
fiducial marks located on the substrate support, several of the
optical and computational techniques previously described in
relation to determining the relative positions of the transfer
blade and substrate are applicable.
[0048] For image capture purposes in FIG. 8, an optical system is
adapted to image through a transparent window located on the
surface of processing chamber. In the embodiment illustrated in
FIG. 8, a single video camera 840 with a CCD array is disposed
above a transparent window 830 located in the upper surface 835 of
the processing chamber. In this illustrated embodiment, the window
is located in the upper surface of the processing chamber, but this
is not required by the present invention. In alternative
embodiments, the window is located in a side surface of the
processing chamber. In another alternative embodiment discussed
below, an optical fiber bundle is utilized, enabling the removal of
the window from the processing chamber. Moreover, although a single
video camera is illustrated in the embodiment illustrated in FIG.
8, this is also not required by the present invention. Multiple
video cameras, multiple still cameras or a single still camera are
utilized in other embodiments.
[0049] The transparent window may be made of any suitable material.
The suitable material generally possesses a degree of optical
transparency and uniformity acceptable for applications of the
present invention. Generally, the optical properties of the window
are invariant with time and temperature. In one embodiment, the
transparent window is made from plexiglass, however this is not
required by the present invention. Other materials can also be
used. In this embodiment, the video camera is positioned to image
at least one location inside the processing chamber. Merely by way
of example, an embodiment according to the present invention
positions the camera to image an area 2''.times.2'' in size.
[0050] The camera used in one embodiment of the present invention
operates over a predetermined wavelength region and at a
predetermined spatial resolution sufficient to capture at least one
image that includes a portion of the substrate and a portion of the
components of the processing chamber disposed inside the chamber.
In a specific embodiment according to the present invention, a
camera operating in the visible region of the electromagnetic
spectrum with a predetermined pixel size is utilized. Merely by way
of example, an embodiment according to the present invention uses a
Sony XC-003 1/3'' 3 CCD color camera, with a resolution of 768
(H).times.494 (V), available from Sony Electronics, Inc., Sony
Business Solutions & Systems Company (BSSC), San Jose,
Calif.
[0051] The camera utilized in embodiments according to the present
invention is generally calibrated to compensate for optical
properties of the transparent window and other components of the
optical system. For example, the index of refraction associated
with the transparent window may vary as a function of position.
Additionally, the thickness of the window may vary as a function of
position. Accordingly, embodiments according to the present
invention utilize a calibration step to compensate for variations
in the optical properties of the transparent window.
[0052] In one embodiment, a substrate with a calibration pattern
present on the upper surface of the substrate is placed on the
substrate support disposed inside the processing chamber. Either an
image or series of images are captured of the calibration pattern
and processed by computer algorithms to calibrate the camera
system. Recalibration of the system can be performed as desired. In
an embodiment according to the present invention, recalibration is
performed after the transfer chamber lid is opened, accidental or
deliberate movement of the camera system, or the like.
[0053] In another embodiment, calibration of the optical system is
performed with the substrate to be processed in place on the
substrate support. FIG. 9 is a simplified schematic illustration of
a perspective cut-away view of a substrate processing chamber and a
substrate support with an integrated calibration field according to
an embodiment of the present invention. In the illustrated
embodiment, the substrate support is fabricated to include an
integrated calibration field on a portion of the substrate support,
the view of which is not obstructed by the substrate. For example,
in FIG. 9, calibration fields 920, 922 and 924 are located on the
substrate support 8 1 0 at positions surrounding the periphery of
the substrate 125. The calibration field in the embodiment
illustrated in FIG. 9 is an optical calibration pattern, but this
is not required by the present invention. For example, a
combination of optical calibration patterns and physical objects
disposed inside the processing chamber could be used for the
calibration process. Merely by way of example, well defined,
accurately inscribed, or machined geometrical patterns may be
used.
[0054] Moreover, in other embodiments according to the present
invention, calibration of the optical system is not limited to
calibration for optical aberrations introduced as a result of the
transparent window. For example, foreshortening of the portions of
the image closest to the camera results in some embodiments.
Foreshortening would occur, for instance, if the optical system
imaged through a window in the side of the processing chamber. As
illustrated in FIG. 9, calibration field 920, nearest the camera,
field 922, at an intermediate distance, and field 924, farthest
from the camera, would most likely present different depths of
field and magnifications to the optical system. Merely by way of
example, adjustment for this foreshortening is accomplished by
creating a mapping between the calibration image obtained by the
optical system and the known dimensions of components of the
processing system present in the chamber. For example, in an
embodiment according to the present invention, the dimensions of
the substrate support are measured and known prior to the
calibration step. After the calibration image is captured, computer
algorithms create a transform map between the known element
positions and the positions of these elements present in the image.
This transform map is utilized in subsequent image processing steps
to account for optical aberrations produced by the optical system.
Alternative mapping systems could utilize multiple images captured
with varied depths of field to further improve the performance of
the optical system. Similar transform maps would be produced by
calibrating the optical system using calibration patterns present
on the surface of a substrate.
[0055] In an embodiment according to the present invention, the
field of view of the optical system is adjusted to image an area
930 as illustrated in FIG. 9. This image contains portions of the
substrate and portions of the calibration field located on the
substrate support. The image is processed by computer algorithms to
determine the center of the substrate support based on the known
positions of the calibration marks 920. Further analysis is
performed to determine the center of the substrate based on the
substrate circumference included in the image. The offset between
the center of the substrate support and the center of the substrate
is calculated. Utilizing the relative offset between the positions
of the substrate and the substrate support, the substrate is
repositioned at the desired position in the processing chamber by
use of the transfer blade. In a specific embodiment, the substrate
is repositioned so that it is centered on the substrate support
within a predetermined tolerance. For example, in a particular
embodiment according to the present invention, the substrate is
centered with a tolerance of less than or equal to 1 mil.
[0056] In an alternative embodiment according to the present
invention, the camera 840 and window 830 shown in FIG. 9 are
replaced with an optical fiber bundle. The optical input side of
the fiber bundle is introduced into the processing chamber through
the chamber surface 835 at the location where the window 830 is
shown in FIG. 9. The use of a fiber bundle in this embodiment
allows for the removal of the window. Light provided by an optical
source (not shown) and reflected off the substrate and substrate
support travels through the fiber bundle to an optical camera
external to the processing chamber, producing. an image of a
portion of the substrate and a portion of the substrate support.
Image processing, as described above, is utilized to calibrate the
optical system and to determine the offset between a predetermined
portion of the substrate and a predetermined portion of the
substrate support. In a particular embodiment according to the
present invention, the predetermined portion of the substrate is
the center of the substrate and the predetermined portion of the
substrate support is the center of the substrate support.
[0057] One of the benefits provided by the use of the optical fiber
bundle is increased flexibility in the placement of the optical
system components. Embodiments according to the present invention
utilizing an optical fiber bundle place the camera and other
components of the optical system in a location separate from the
substrate processing system.
[0058] FIG. 10 is a simplified flowchart of a method of positioning
a substrate in a processing chamber in accordance with an
embodiment of the present invention. First, a substrate supported
by a transfer blade is transferred to a processing chamber by a
transfer robot and placed on a substrate support disposed inside
the processing chamber. The optical system is calibrated to account
for variations in the optical uniformity of the optical system.
Next, at least one image is captured that includes at least a
portion of the components of the processing chamber disposed inside
the chamber and at least a portion of the substrate. The captured
image is processed using computer algorithms to determine the
position of a predetermined portion of the components. In one
embodiment, the predetermined portion of the components is the
center of the substrate support. Additionally, the captured image
is processed using computer algorithms to determine the position of
a predetermined portion of the substrate. In one embodiment, the
predetermined portion of the substrate is the center of the
substrate, which is a semiconductor wafer. An offset between the
two positions is calculated in the next step. If the offset exceeds
a system tolerance, the transfer blade is utilized to reposition
the substrate at a predetermined location on the substrate support.
After repositioning, in one embodiment according to the present
invention, the steps of the method starting with system calibration
are repeated to verify the placement location of the substrate.
Thus, the substrate is repositioned in the processing chamber with
increased accuracy.
[0059] While the above is a complete description of specific
embodiments of the invention, the above description should not be
taken as limiting the scope of the invention as defined by the
claims.
* * * * *