U.S. patent application number 12/173857 was filed with the patent office on 2009-01-29 for optical spot geometric parameter determination using calibration targets.
Invention is credited to Clemente Bottini, Ronald D. Fiege, Roger M. Young, Shahin Zangooie, Lin Zhou.
Application Number | 20090027660 12/173857 |
Document ID | / |
Family ID | 38985890 |
Filed Date | 2009-01-29 |
United States Patent
Application |
20090027660 |
Kind Code |
A1 |
Zangooie; Shahin ; et
al. |
January 29, 2009 |
OPTICAL SPOT GEOMETRIC PARAMETER DETERMINATION USING CALIBRATION
TARGETS
Abstract
A method, system and computer program product for determining a
geometric parameter of an optical spot of a light beam are
disclosed. A method comprises: providing a calibration target, the
calibration target including a systematic variation in a parameter;
measuring the calibration target with respect to the systematic
variation using the light beam to obtain a plurality of
measurements; and analyzing the measurements and the systematic
variation to determine the geometric parameter of the optical
spot.
Inventors: |
Zangooie; Shahin; (Hopewell
Junction, NY) ; Young; Roger M.; (Warwick, NY)
; Zhou; Lin; (LaGrangeville, NY) ; Bottini;
Clemente; (Marlboro, NY) ; Fiege; Ronald D.;
(Hopewell Junction, NY) |
Correspondence
Address: |
HOFFMAN WARNICK LLC
75 STATE ST, 14TH FL
ALBANY
NY
12207
US
|
Family ID: |
38985890 |
Appl. No.: |
12/173857 |
Filed: |
July 16, 2008 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11828666 |
Jul 26, 2007 |
|
|
|
12173857 |
|
|
|
|
Current U.S.
Class: |
356/121 |
Current CPC
Class: |
G03F 7/70516
20130101 |
Class at
Publication: |
356/121 |
International
Class: |
G01B 9/08 20060101
G01B009/08 |
Claims
1. A calibration target for measuring a size of an optical spot of
a light beam, the calibration target comprising: a first portion, a
dimension of which in a first axis systematically decreases along a
second axis; a second portion; and a third portion; wherein the
second portion and the third portion extend along opposite sides of
the first portion and are separated by the first portion in the
first axis, and include a material of different optical response
than that of the first portion.
2. A calibration target for measuring a level of symmetry of an
optical spot of a light beam, the calibration target comprising: a
gradient in a parameter along an axis of the calibration target,
the gradient being a function of the axis, and including one of: a
continuous gradient from one end of the calibration target to
another end thereof in the axis; or a switch point in a given point
of the calibration target in the axis between two sub-gradients,
one of the two sub-gradients being an ascending gradient and the
other being a descending gradient.
Description
REFERENCE TO PRIOR APPLICATIONS
[0001] This application is a continuation application of co-pending
U.S. patent application Ser. No. 11/828,666 filed on Jul. 26, 2007,
which is hereby incorporated by reference.
BACKGROUND OF THE DISCLOSURE
[0002] 1. Technical Field
[0003] The present disclosure relates in general to a processing
system, and more particularly to determining a geometric parameter
of an optical spot of a light beam of an optical metrology tool
used in the processing system.
[0004] 2. Background Art
[0005] Utilization of optical metrology in semiconductor
manufacturing has grown significantly over the past several years.
The technology provides capabilities to conduct measurements of a
wide variety of critical device parameters, including, e.g.,
critical dimensions, depths and sidewall angles. Benefits of
optical metrology include non-contact measurement capability that
can be performed very quickly.
[0006] For optical metrology tools to yield reliable measurements,
it is necessary that the tools produce well defined light beams,
and collect the optical response for analysis, as designed. The
size of the optical spot of the produced light beam, which is
defined as the area illuminated by the incident light beam, can
have a large impact on the measurement values. As a consequence,
for example, the sizes of the optical spots of optical metrology
tools affects the matching performance of the optical metrology
tools.
[0007] An optical spot can initially appear to be symmetric. An
optical spot may have an area (usually referred to as an "effective
spot") inside the optical spot, which provides most, e.g., 99%, of
the information content. An effective spot is very sensitive to the
small change in the area it illuminates. Usually, an effective spot
comprises a small portion of a total optical spot. For example, the
entire optical spot may illuminate an area of 1600 square microns,
while the most sensitive area of the optical spot (i.e., the
effective spot) may be a 100 square micron area. If the optical
spot is symmetric, the effective spot will be located in the center
of the optical spot. If the optical spot is not symmetric, then the
effective spot will be located off the center of the optical spot.
Whether an optical spot of an optical metrology tool is symmetric
and the level of symmetry impact the measurement result and thus
the matching of the optical metrology tools.
[0008] Conventional approaches to optical metrology do not have a
satisfactory solution to characterize a geometric parameter of an
optical spot and or or a level of symmetry of the optical spot.
SUMMARY
[0009] A first aspect of the disclosure is directed to a method for
determining a geometric parameter of an optical spot of a light
beam, the method comprising: providing a calibration target, the
calibration target including a systematic variation in a parameter;
measuring the calibration target with respect to the systematic
variation using the light beam to obtain a plurality of
measurements; and analyzing the measurements and the systematic
variation to determine the geometric parameter of the optical
spot.
[0010] A second aspect of the disclosure is directed to a system
for determining a geometric parameter of an optical spot of a light
beam, the method comprising: [0011] means for controlling a
calibration target, the calibration target including a systematic
variation in a parameter; means for measuring the calibration
target with respect to the systematic variation using the light
beam to obtain a plurality of measurements; and means for analyzing
the measurements and the systematic variation to determine the
geometric parameter of the optical spot.
[0012] A third aspect of the disclosure is directed to a
calibration target for measuring a size of an optical spot of a
light beam, the calibration target comprising: a first portion, a
dimension of which in a first axis systematically decreases along a
second axis; a second portion; and a third portion; wherein the
second portion and the third portion extend along opposite sides of
the first portion and are separated by the first portion in the
first axis, and include a material of different optical response
than that of the first portion.
[0013] A fourth aspect of the disclosure is directed to a
calibration target for measuring a level of symmetry of an optical
spot of a light beam, the calibration target comprising: a gradient
in a parameter along an axis of the calibration target, the
gradient being a function of the axis, and including one of: a
continuous gradient from one end of the calibration target to
another end thereof in the axis; or a switch point in a given point
of the calibration target in the axis between two sub-gradients,
one of the two sub-gradients being an ascending gradient and the
other being a descending gradient.
[0014] Other aspects and features of the present disclosure, as
defined solely by the claims, will become apparent to those
ordinarily skilled in the art upon review of the following
non-limited detailed description of the disclosure in conjunction
with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The embodiments of this disclosure will be described in
detail, with reference to the following figures, wherein like
designations denote like elements, and wherein:
[0016] FIG. 1 shows a block diagram of a system according to the
disclosure.
[0017] FIGS. 2-3 show embodiments of calibration targets for
measuring a size of an optical spot.
[0018] FIG. 4 shows embodiments of a method for measuring the size
of the optical spot using calibration targets of FIGS. 2-3.
[0019] FIG. 5-6 show embodiments of calibration targets for
measuring a level of symmetry of an optical spot.
[0020] FIG. 7 shows embodiments of a method for measuring the level
of symmetry of the optical spot using calibration targets of FIGS.
5-6.
[0021] It is noted that the drawings of the disclosure are not to
scale. The drawings are intended to depict only typical aspects of
the disclosure, and therefore should not be considered as limiting
the scope of the disclosure. In the drawings, like numbering
represents like elements among the drawings.
DETAILED DESCRIPTION OF THE DISCLOSURE
[0022] The following detailed description of embodiments refers to
the accompanying drawings, which illustrate specific embodiments of
the disclosure. Other embodiments having different structures and
operations do not depart from the scope of the present
disclosure.
1. System Overview
[0023] FIG. 1 shows a block diagram of a system 10 according to an
embodiment of the invention. System 10 includes multiple optical
metrology tools (tool) 12. Each tool 12 can produce a light beam 14
having an optical spot 16 (shown in FIG. 2) on a calibration target
20. System 10 includes a processing system 22 including a
calibration target controlling unit 24, a measurement controlling
unit 26, an analysis unit 28 including an optical response monitor
40, a relative scan position adjusting unit 42 and an operation
controlling unit 44. System 10 also includes a tool matching unit
29.
2. Measuring Optical Spot Size
[0024] FIG. 2 shows a calibration target 20 with multiple optical
spots 16 thereon. Calibration target 20 includes a first portion
202, a second portion 204 and a third portion 206. Second portion
204 and third portion 206 extending along opposite sides 210, 212
of first portion 202, and are separated by first portion 202 in the
y-axis. Second portion 204 and third portion 206 may further
completely emborder first portion 202 (not shown). Second portion
204 and third portion 206 include a material of different optical
response than that of first portion 202 such that when an optical
spot 16 moves (partially or totally) from first portion 202 to at
least one of second portion 204 or third portion 206, a change will
be detected in the reflected beam collected by, e.g., tool 12.
Within each portion, the optical response is substantially
uniform.
[0025] An y-axis dimension of first portion 202 in y-axis
systematically decreases along x-axis. In this description, the
term "systematic" is used for its meaning in statistics and is
opposite to "random". A systematic variation is a non-random
variation, e.g., continuous decreasing, continuous increasing,
first increasing and then decreasing, gradient, etc. According to
an embodiment, as shown in FIG. 2, the decreasing of the y-axis
dimension is in a continuous manner such that, in a two-dimensional
view, first portion 202 has a substantially trapezoidal shape.
According to an alternative embodiment, as shown in FIG. 3, in a
two-dimensional view, a first portion 302 of a calibration target
30 has a substantially stepped-side trapezoidal shape, i.e., it has
two ladder-shaped borders 310, 312.
[0026] FIG. 4 shows, in a flow diagram, embodiments of a method for
measuring a size of an optical spot 16 using calibration target 20.
In the following description, calibration target 20 of FIG. 2 will
be used as an example to describe the method of FIG. 4. It should
be appreciated that calibration target 30 of FIG. 3 may be
similarly used. Referring to FIGS. 1-2 and 4 collectively, in
process S1, measurement controlling unit 26 and calibration target
controlling unit 24 coordinate to control a tool 12 to measure
calibration target 20 with respect to the systematic variation,
i.e., the decreasing of the y-axis dimension, using the respective
light beam 14 to obtain a plurality of measurements. Specifically,
the measuring includes scanning light beam 14 along calibration
target 20 in x-axis to make measurements of the optical response of
calibration target 20. For example, at the beginning of the scan,
optical spot 16 is positioned to be totally within first portion
202, as represented by optical spot 16a, and the scanning may
follow the x-axis along which the y-axis dimension of calibration
target 20 decreases. However, other scanning procedure is also
possible. For example, optical spot 16 may be initially positioned
to cover all three portions 202, 204 and 206, and the scanning may
follow the direction that the y-axis dimension of calibration
target 20 increases.
[0027] In process S2, analysis unit 28 analyzes the measurements
and change of y-axis dimension of calibration target 20 to
determine the size of optical spot 16. Specifically, analysis unit
28 relates a measurement of the optical response to a position of
optical spot 16 with respect to first portion 202, second portion
204 and third portion 206 of calibration target 20 to identify a
reference scan position of optical spot 16 where optical spot 16 is
marginally located within first portion 202, i.e., optical spot 16
is substantially tangential to both borders 210, 212. That is, the
"reference scan position" corresponds to a smallest y-axis
dimension of first portion 202 that can still enclose optical spot
16. Any method may be used to identify the reference scan position,
and all are included. For example, according to an embodiment, in
sub-process S2-1, optical response monitor 40 detects a change of
value in the measured calibration target 20 optical response
indicating that optical spot 16 covers a portion of first portion
202 and a portion of at least one of second portion 204 and third
portion 206. Optical spot 16b represents this situation.
[0028] In sub-process S2-2, relative scan position adjusting unit
42 adjusts a relative position between optical spot 16 and the
calibration target 20 in the y-axis to locate optical spot 16
within first portion 202. For example, with respect to optical spot
16b, relative scan position adjusting unit 42 may instruct
calibration target controlling unit 24 to move calibration target
202 upward or may instruct measurement controlling unit 26 to move
optical spot 16b downward.
[0029] In sub-process S2-3, operation controlling unit 44
determines whether the position-adjusted optical spot 16 is
completely located within first portion 202. If "yes", operation
controlling unit 44 proceeds to process S-1. That is, the scanning,
detecting and adjusting is continued from the current scan position
of optical spot 16. If "no", in sub-process S2-4, analysis unit 44
identifies the last scan position of optical spot 16 where optical
spot 16 is located completely within first portion 202 as the
reference scan position.
[0030] In process S3, analysis unit 28 determines a size of optical
spot 16 in the y-axis based on the dimension of first portion 202
in the y-axis which corresponds to the reference scan position. The
corresponding dimension is the largest y-axis dimension of first
portion 202 from a point in border 210 or 212 of first portion 202
which is closest to optical spot 16 in the reference scan position.
For example, for optical spot 16c of FIG. 2, border point 46 and 48
are the closest points and dimension 50 is the corresponding
dimension. FIG. 2 shows that the dimensions from border points 46
and 48 are the same, which is not necessary. For example, if
optical spot 16 is not symmetric, dimensions from border points 46
and 48 may be different and the larger one will be identified as
the corresponding dimension. The size of optical spot 16 in the
y-axis will be determined as substantially equal to the
corresponding dimension.
[0031] Following the similar procedure, size of optical spot 16 in
other axis or direction may be determined. For example, calibration
target 20 may be rotated 90 degrees and optical spot 16 will be
scanned along the y-axis to determine an x-axis size of optical
spot 16 following the similarly procedures described above.
[0032] According to an embodiment, analysis unit 28 may also
determine a relative position between two optical spots 16 based on
the adjusting in the y-axis made for each of the two optical spots
16. As shown in FIG. 3, e.g., if two optical spots 116a and 116b
are adjusted differently (shown by different distances 118a, 118b)
in the y-axis to reach the respective reference scan positions, it
is determined that centers 120a and 120b of optical spots 116a and
116b, as before adjustments, are separated from one another in the
y-axis.
[0033] In addition, processing system 22 may further determine a
size of optical spot 16 using calibration targets with differences
in another parameter different than the y-axis dimension to
determine a variation of the determined size of optical spot 16
based on the difference in the another parameter. For example,
processing system 22 may measure the size of optical spot 16 using
calibration targets 20 of different combinations of optical
responses, and/or critical dimensions to determine the possible
variations in the measured sizes of optical spot 16.
3. Measuring Optical Spot Symmetry
[0034] FIG. 5 shows an embodiment of a calibration target 60 for
measuring a level of symmetry of an optical spot 16. Calibration
target 60 includes a gradient 62 in a parameter along the x-axis.
The gradient parameter may be any parameter whose change can be
detected by the effective spot of optical spot 16. For example, the
parameter may be optical response, critical dimensions, height or
depth of grating line, etc. In the current description, a density
of grating lines 64 (hereinafter "density") of calibration target
60 may be used for the gradient parameter. Preferably, the density
gradient is a function of the x-axis.
[0035] According to an embodiment, as shown in FIG. 5, the density
gradient 62 is continuous from one end of calibration target 60 to
another end thereof in the x-axis. According to an another
embodiment, as shown in FIG. 6, the density gradient 162 includes
two sub-gradients 162a and 162b separated by a switch point 166 in
a given point in x-axis, e.g., in the center of calibration target
160. Along the x-axis, sub-gradient 162a is an ascending gradient
(i.e., density increasing along the x-axis), and sub-gradient 162b
is a descending one (i.e., density decreasing along the
x-axis).
[0036] FIG. 7 shows embodiments of a method for measuring a level
of symmetry of optical spot 16. A level of symmetry is determined
based on whether the effective spot is in the center of the optical
spot and how far away the effective spot deviates from the center
of the optical spot. Referring to FIGS. 1, 5 and 7, in process S11,
measurement controlling unit 26 locates optical spot 16 with an
effective spot 17 on a given point, e.g., the center 66, and scans
optical spot 16 from the given point along gradient 62 or 162 in
different directions to obtain multiple measurements of the
density. In process S12, analysis unit 28 analyzes the differences
in the measured density to determine whether effective spot 17 is
in the center of optical spot 16, and/or how far away effective
spot 17 deviates from the center of optical spot 16. Any method may
be used in the analysis, and all are included. For example, where
calibration target 60 is used for the measurement, measurement
controlling unit 26 may scan optical spot 16 from center 66 to the
low density end 68 (as shown by arrow 67) along the x-axis and
obtain a first set of measurements. Then, calibration target
controlling unit 24 may position calibration target 60 with a 180
degree rotation as shown in phantom 60a. Measurement controlling
unit 26 may scan optical spot 16 from center 66 to the low density
end 68 (as shown by dotted arrow 67a along the x-axis) and obtain a
second set of measurements. If the second set of measurements does
not match the first set of measurements, it can be determined that
effective spot 17 is not located in the center of optical spot 16.
Alternatively, calibration target controlling unit 24 may position
calibration target 60 with a 90 degree rotation as shown in phantom
60b. Measurement controlling unit 26 may scan optical spot 16 from
center 66 to the low density end 68 (as shown by dotted arrow 67b
along the z-axis) and obtain a third set of measurements. If the
third set of measurements does not match the first set of
measurements, it can be determined that effective spot 17 is not
located in the center of optical spot 16. In addition, by comparing
the differences in the different sets of measurement, analysis unit
28 may be able to determine how far away effective spot 17 deviates
from the center of optical spot 16.
[0037] Referring to FIGS. 1 and 6-7, where calibration target 160
is used, measurement controlling unit 26 may first locate optical
spot 16 in the center 166 of calibration target 160 and scan
optical spot 16 from center 166 to both sides along sub-gradient
162a and 162b in x-axis. If measurements from both sides of the
scanning show increases in the density, it is determined that the
effective spot 17 (FIG. 5) is in the center of optical spot 16
(FIG. 5). If measurements from one side of scanning show a switch
point (e.g., change from density decreasing to density increasing)
in the density, it is determined that the effective spot 17 (FIG.
5) is not in the center of optical spot 16 (FIG. 5). In addition,
by relating the detected switch point to the scan position of
optical spot 16, analysis unit 28 may be able to determine how far
away effective spot 17 (FIG. 5) deviates from the center of optical
spot 16 (FIG. 5).
[0038] The determined geometric parameter of optical spot 16, e.g.,
size, level of symmetry, may be output to, e.g., tool matching unit
29 for matching tools 12 based on the respective optical spot 16
geometric parameters. For example, tool matching unit 29 may adjust
the measurements of each tools 12 based on the respective sizes
and/or levels of symmetry of optical spots 16. Tool matching unit
29 may also physically adjust each tool 12 regarding the optical
spot 16 geometric parameters. Other uses of the determined sizes
and/or levels of symmetry of light beams 14 of tools 12 are also
possible and included in the disclosure. For example, the
calibration targets described above may be used in a semi real time
feedback control system to measure geometric parameters of optical
spots during system manufacturing, optics alignment and preventive
maintenance.
[0039] According to an embodiment, processing system 22 may be
implemented by a computer system. The computer system can comprise
any general purpose computing article of manufacture capable of
executing computer program code installed thereon to perform the
process described herein. The computer system can also comprise any
specific purpose computing article of manufacture comprising
hardware and/or computer program code for performing specific
functions, any computing article of manufacture that comprises a
combination of specific purpose and general purpose hardware or
software, or the like. In each case, the program code and hardware
can be created using standard programming and engineering
techniques, respectively.
4. Conclusion
[0040] While shown and described herein as a method and system for
determining a geometric parameter of an optical spot of a light
beam, it is understood that the disclosure further provides various
alternative embodiments. For example, in an embodiment, the
disclosure provides a program product stored on a computer-readable
medium, which when executed, enables a computer infrastructure to
determine a geometric parameter of an optical spot of a light beam.
To this extent, the computer-readable medium includes program code,
which may be installed to a computer system to implement, e.g.,
processing system 22 (FIG. 1), to implement the process described
herein. It is understood that the term "computer-readable medium"
comprises one or more of any type of physical embodiment of the
program code. In particular, the computer-readable medium can
comprise program code embodied on one or more portable storage
articles of manufacture (e.g., a compact disc, a magnetic disk, a
tape, etc.), on one or more data storage portions of a computing
device, such as a memory and/or a storage system and/or as a data
signal traveling over a network (e.g., during a wired or wireless
electronic distribution of the program product).
[0041] It should be appreciated that the teachings of the present
disclosure could be offered as a business method on a subscription
or fee basis. For example, a system 10 (FIG. 1) including
processing system 22 and calibration targets 20, 30, 60 and 160
could be created, maintained and/or deployed by a service provider
that offers the functions described herein for customers. That is,
a service provider could offer to determine a geometric parameter
of an optical spot of a light beam as described above.
[0042] As used herein, it is understood that the terms "program
code" and "computer program code" are synonymous and mean any
expression, in any language, code or notation, of a set of
instructions that cause a computing device having an information
processing capability to perform a particular function either
directly or after any combination of the following: (a) conversion
to another language, code or notation; (b) reproduction in a
different material form; and or or (c) decompression. To this
extent, program code can be embodied as one or more types of
program products, such as an application or software program,
component software or a library of functions, an operating system,
a basic I or O system or driver for a particular computing and/or I
or O device, and the like. Further, it is understood that the terms
"component" and "system" are synonymous as used herein and
represent any combination of hardware and/or software capable of
performing some function(s).
[0043] The flowcharts and block diagrams in the Figures illustrate
the architecture, functionality, and operation of possible
implementations of systems, methods and computer program products
according to various embodiments of the present disclosure. In this
regard, each block in the flowchart or block diagrams may represent
a module, segment, or portion of code, which comprises one or more
executable instructions for implementing the specified logical
function(s). It should also be noted that, in some alternative
implementations, the functions noted in the blocks may occur out of
the order noted in the figures. For example, two blocks shown in
succession may, in fact, be executed substantially concurrently, or
the blocks may sometimes be executed in the reverse order,
depending upon the functionality involved. It will also be noted
that each block of the block diagrams and or or flowchart
illustration, and combinations of blocks in the block diagrams and
or or flowchart illustration, can be implemented by special purpose
hardware-based systems which perform the specified functions or
acts, or combinations of special purpose hardware and computer
instructions.
[0044] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the disclosure. As used herein, the singular forms "a", "an" and
"the" are intended to include the plural forms as well, unless the
context clearly indicates otherwise. It will be further understood
that the terms "comprises" and/or "comprising," when used in this
specification, specify the presence of stated features, integers,
steps, operations, elements, and/or components, but do not preclude
the presence or addition of one or more other features, integers,
steps, operations, elements, components, and/or groups thereof.
[0045] Although specific embodiments have been illustrated and
described herein, those of ordinary skill in the art appreciate
that any arrangement which is calculated to achieve the same
purpose may be substituted for the specific embodiments shown and
that the disclosure has other applications in other environments.
This application is intended to cover any adaptations or variations
of the present disclosure. The following claims are in no way
intended to limit the scope of the disclosure to the specific
embodiments described herein.
* * * * *