EP1063570A2
Expired / Lapsed
EP
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In situ projection optic metrology method and apparatus
Assignee: ASML Holding NV
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Filing: 2000-06-21
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Granted: —
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Expires: 2020-06-21
Abstract
Abstract Wavefront information for an optical system is calculated based on the intensity of an image of a plurality of gratings (16) having different periods and orientations taken from at least two different planes a predetermined distance apart. The image of a plurality of gratings having different spatial frequencies or periods and orientations, the location of which are precisely known, are imaged in a nominal focal plane (28) of the optical system, and, preferably, in two additional planes (26, 30) displaced a predetermined distance from the nominal focal plane (28). The phase shift, if any, from a fundamental frequency of the image intensity, is determined based on the known location of the grating (16) and the grating image intensity (40, 48, 50). The grating image intensity is detected and measured in a first detection plane in a nominal focal plane (38) and in a second detection plane a predetermined distance from the nominal focal plane (36, 40). From these measurements wavefront information is calculated. By utilizing a plurality of different gratings, the wavefront at different spatial locations in the optical system may be mapped, providing information relating to image quality. The present invention provides wavefront information, which is directly related to image quality, relatively easily and without having to remove the optical system from the device, such as a photolithographic device used in semiconductor manufacturing. The present invention is particularly applicable to optical systems designed for UV illumination, which tends to degrade or modify optics over time. More consistent, better quality imaging is obtained with reduced down time.
Inventors
- 👤 Justin L. Kreuzer
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-07 14:56
CPC Classifications
G; G01; G01N; G01N21/00; G03; G03F; G03F7/00; G03F7/70; G03F7/70483; G03F7/70591; G03F7/706
Claims Analysis
Total Claims: 26
Claim 1
Independent Claim
164 words
An apparatus for measuring a wavefront of an optical
system comprising: a reticle stage having a known first location; a reticle, placed on said reticle stage, said reticle having
a plurality of gratings with different periods and orientations
placed thereon; an optical system positioned to receive electromagnetic
radiation passing through said reticle, said optical system
having an optical axis and a nominal focus; an image stage having a known second location positioned to
receive electromagnetic radiation passing through said optical
system, said image stage movable in a direction substantially
perpendicular to the optical axis and capable of moving a
predetermined distance away from the nominal focus, whereby an
image of the plurality of gratings with different periods and
orientations is formed; a detector, said detector detecting the image of each of the
plurality of gratings with different periods and orientations in
at least two different planes; and a calculator coupled to said detector and said reticle and
image stages, said calculator calculating wavefront information.
Claim 2
Dependent Claim
28 words
An apparatus for measuring a wavefront of an optical
system as in claim 1 wherein: each of said plurality of gratings have equally spaced
opaque and transparent portions.
Claim 3
Dependent Claim
26 words
An apparatus for measuring a wavefront of an optical
system as in claim 1 wherein: each of said plurality of gratings has at least five cycles.
Claim 4
Dependent Claim
26 words
An apparatus for measuring a wavefront of an optical
system as in claim 1 wherein: said plurality of gratings are arranged forming a plurality
of sections.
Claim 5
Dependent Claim
32 words
An apparatus for measuring a wavefront of an optical
system as in claim 4 wherein: each of said plurality of sections has a dimension less than
the spatial variance of the wavefront.
Claim 6
Dependent Claim
28 words
An apparatus for measuring a wavefront of an optical
system as in claim 5 wherein: each of said plurality of sections has a dimension less than
one millimeter.
Claim 7
Dependent Claim
35 words
An apparatus for measuring a wavefront of an optical
system as in claim 5 wherein: the gratings in any single section can be placed within a
square of side one millimeter by reticle stage travel.
Claim 8
Dependent Claim
20 words
An apparatus for measuring a wavefront of an optical
system as in claim 1 further comprising: a point illumination source.
Claim 9
Dependent Claim
20 words
An apparatus for measuring a wavefront of an optical
system as in claim 1 further comprising: an extended illumination source.
Claim 10
Dependent Claim
95 words
An apparatus for measuring a wavefront of an optical
system as in claim 1 wherein: said calculator calculates the wavefront information based
upon the following equation, l (α,ρ, z ) = cos 2π x P + w (α) odd X cos 2π w (α) even - w (0)+ z λ ( 1-α 2 -1) where, α = λ P and, λ is the wavelength of the light, P is the grating period, x is the distance measured along a line perpendicular to the
grating lines, and Z is the distance from the nominal focal plane.
Claim 11
Dependent Claim
44 words
An apparatus for measuring a wavefront of an optical
system as in claim 10 wherein: said calculator calculates the wavefront information based
upon the equation and its extension to the image of the
fundamental frequency of a grating illuminated with an extended
illumination source.
Claim 12
Independent Claim
197 words
An apparatus for obtaining wavefront information for an
optical system in a photolithographic device comprising: a reticle having a plurality of gratings with different
periods and orientations formed thereon; a reticle stage positioning said reticle at a first
location; an image stage, said image stage capable of moving a
predetermined distance out of a nominal focal plane of the
optical system and being positioned at a second location; an illumination source projecting an image of each of said
plurality of gratings through the optical system; an image intensity detector detecting the intensity of the
image of each of the plurality of gratings in the nominal focal
plane and at a predetermined distance out of the nominal focal
plane; and a wavefront information calculator, coupled to said image
intensity detector and said reticle and image stages, said
wavefront information calculator calculating wavefront
information based on the first location of said reticle stage,
the second location of said image stage, and the image intensity
detected in at least the nominal focal plane and the
predetermined distance out of the nominal focal plane, whereby wavefront information is calculated and changes in
the performance of the projection optic can be detected.
Claim 13
Dependent Claim
32 words
An apparatus for obtaining wavefront information for an
optical system in a photolithographic device as in claim 12
wherein: each of said plurality of gratings have equally spaced
opaque and transparent portions.
Claim 14
Dependent Claim
30 words
An apparatus for obtaining wavefront information for an
optical system in a photolithographic device as in claim 12
wherein: said plurality of gratings are arranged forming a plurality
of sections.
Claim 15
Dependent Claim
36 words
An apparatus for obtaining wavefront information for an
optical system in a photolithography device as in claim 14
wherein: each of said plurality of sections has a dimension less than
the spatial variance of the wavefront.
Claim 16
Dependent Claim
32 words
An apparatus for obtaining wavefront information for an
optical system in a photolithography device as in claim 14
wherein: each of said plurality of sections has a dimension less than
one millimeter.
Claim 17
Dependent Claim
39 words
An apparatus for obtaining wavefront information for an
optical system in a photolithographic device as in claim 14
wherein: the gratings in any single section can be placed within a
square of side one millimeter by reticle stage travel.
Claim 18
Dependent Claim
44 words
An apparatus for obtaining wavefront information for an
optical system in a photolithographic device as in claim 12
further comprising: an adjuster, said adjuster coupled to said wavefront
information calculator and the projection optics, and capable of
adjusting the projection optics modifying the wavefront.
Claim 19
Dependent Claim
101 words
An apparatus for obtaining wavefront information for an
optical system in a photolithographic device as in claim 12
wherein: said wavefront information calculator calculates the
wavefront information based upon the following equation, l (α,ρ, z ) = cos 2π x P + w (α) odd X cos 2π w (α) even - w (0)+ z λ ( 1-α 2 -1) where, α = λ P and, λ is the wavelength of the light, P is the grating period, x is the distance measured along a line perpendicular to the
grating lines, and Z is the distance from the nominal focal plane.
Claim 20
Dependent Claim
48 words
An apparatus for obtaining wavefront information for an
optical system in a photolithographic device as in claim 19
wherein: said calculator calculates the wavefront information based
upon the equation and its extension to the image of the
fundamental frequency of a grating illuminated with an extended
illumination source.
Claim 21
Independent Claim
231 words
An apparatus for measuring a wavefront of an optical
system for use in a photolithographic device comprising: a plurality of gratings with different periods and
orientations, each of said plurality of gratings having a first
location; an optical system positioned to receive electromagnetic
radiation passing through said reticle, said optical system
having an optical axis and a nominal focus; image means for receiving an image of each of said plurality
of gratings projected through said optical system, and capable of
moving a predetermined distance away from the nominal focus along
the optical axis, whereby an image of the plurality of gratings
is formed at a second location displaced relative to the optical
axis from the first location; detector means, associated with said image means, for
detecting the image of each of said plurality of gratings at the
nominal focus and the predetermined distance away from the
nominal focus; and calculator means, coupled to said detector means, for
calculating wavefront information based upon image intensity of
the image of each of said plurality of gratings at the nominal
focus and the predetermined distance away from the nominal focus
and any displacement relative to the optical axis between the
first location of each of the plurality of gratings and the
second location of the image of the plurality of gratings, whereby changes in wavefront can be detected providing
information relating to image quality.
Claim 22
Dependent Claim
102 words
An apparatus for measuring a wavefront of an optical
system for use in a photolithographic device as in claim 21
wherein: said calculator means calculates the wavefront information
based upon the following equation, l (α,ρ, z ) = cos 2π x P + w (α) odd X cos 2π w (α) even - w (0)+ z λ ( 1-α 2 -1) where, α = λ P and, λ is the wavelength of the light, P is the grating period, x is the distance measured along a line perpendicular to the
grating lines, and Z is the distance from the nominal focal plane.
Claim 23
Dependent Claim
50 words
An apparatus for measuring a wavefront of an optical
system for use in a photolithographic device as in claim 22
wherein: said calculator calculates the wavefront information based
upon the equation and its extension to the image of the
fundamental frequency of a grating illuminated with an extended
illumination source.
Claim 24
Independent Claim
161 words
A method of determining wavefront information for an
optical system comprising the steps of: locating a reticle having a plurality of gratings thereon
with different periods and orientations such that each of the
plurality of gratings has a known location; forming an image of each of the plurality of gratings with
the optical system; detecting the image of each of the plurality of gratings in
a nominal focal plane and a first plane a predetermined distance
from the nominal focal plane, each image having an illumination
intensity; determining the location of the image of each of the
plurality of gratings relative to the known location of each of
the plurality of gratings; and calculating wavefront information based upon the location of
the image of each of the plurality of gratings relative to the
known location of each of the plurality of gratings, and the
illumination intensity, whereby wavefront information is obtained providing an
indication of any change in the optical system.
Claim 25
Dependent Claim
99 words
A method of determining wavefront information for an
optical system as in claim 24 wherein: said step of calculating wavefront information calculates
the wavefront information based upon the following equation, l (α,ρ, z ) = cos 2π x P + w (α) odd X cos 2π w (α) even - w (0)+ z λ ( 1-α 2 -1) where, α = λ P and, λ is the wavelength of the light, P is the grating period, x is the distance measured along a line perpendicular to the
grating lines, and Z is the distance from the nominal focal plane.
Claim 26
Dependent Claim
48 words
A method of determining wavefront information for an
optical system as in claim 25 wherein: said step of calculating wavefront information calculates
the wavefront information based upon the equation and its
extension to the image of the fundamental frequency of a grating
illuminated with an extended illumination source.
References Cited (Backward Citations)
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