U.S. patent application number 09/853631 was filed with the patent office on 2001-10-04 for position transducer and exposure apparatus with same.
This patent application is currently assigned to NIKON CORPORATION. Invention is credited to Inoue, Jiro, Ota, Kazuya.
Application Number | 20010026357 09/853631 |
Document ID | / |
Family ID | 27310794 |
Filed Date | 2001-10-04 |
United States Patent
Application |
20010026357 |
Kind Code |
A1 |
Ota, Kazuya ; et
al. |
October 4, 2001 |
Position transducer and exposure apparatus with same
Abstract
The exposure apparatus is provided in its main body portion with
laser diodes each having different wavelengths, for illuminating
light for alignment onto a mark of a grating form arranged on each
of a reticle and a wafer. The main body portion of the exposure
apparatus has photomultipliers for receiving the diffraction light
returned from each of the reticle mark and the wafer mark. The
alignment of the reticle mark with the wafer mark is implemented by
comparing phase differences of optical beat signals converted
photoelectrically by the photomultipliers and by means of a phase
detection comparison system. The light fluxes are transmitted
between photomultipliers the laser diodes and the alignment optical
system disposed in the main body portion thereof through optical
fibers. This arrangement enables the position transducer to reduce
an influence of generated heat upon the position detection of the
wafer as well as the exposure apparatus, even if a photodetector
having a large calorific power is employed.
Inventors: |
Ota, Kazuya; (Tokyo, JP)
; Inoue, Jiro; (Kanagawa-ken, JP) |
Correspondence
Address: |
ARMSTRONG,WESTERMAN, HATTORI,
MCLELAND & NAUGHTON, LLP
1725 K STREET, NW, SUITE 1000
WASHINGTON
DC
20006
US
|
Assignee: |
NIKON CORPORATION
Tokyo
JP
|
Family ID: |
27310794 |
Appl. No.: |
09/853631 |
Filed: |
May 14, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09853631 |
May 14, 2001 |
|
|
|
08847480 |
Apr 25, 1997 |
|
|
|
Current U.S.
Class: |
355/53 |
Current CPC
Class: |
G03F 9/7049
20130101 |
Class at
Publication: |
355/53 |
International
Class: |
G03B 027/42 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 26, 1996 |
JP |
106651/1996 |
Apr 26, 1996 |
JP |
106650/1996 |
Claims
What is claimed is:
1. A position transducer for detecting a position of an substrate,
comprising: an illumination optical system for illuminating a light
flux for detecting the position of said substrate on a mark for
position detection provided on said substrate; a photodetector for
receiving the light flux from said mark for position detection; and
plural optical guides for leading the light flux returning from
said mark for position detection to said photodetector.
2. A position transducer as claimed in claim 1, wherein: said light
flux for position detection comprises a light flux of multiple
wavelengths; and the light flux from said mark for position
detection is led to said photodetector through said plural optical
guide different for each wavelength.
3. A position transducer as claimed in claim 2, wherein each of
said plural optical guides comprises an optical fiber with a
propagation efficiency optimized for the wavelength of the light
flux as an object of propagation.
4. A position transducer as claimed in any one of claims 1 to 3,
wherein: said mark for position detection comprises a mark of a
diffraction grating form arranged by a predetermined pitch in a
direction of measurement; said illumination optical system
comprises an optical system for illuminating mutually coherent
multiple light fluxes as said light flux for position detection on
the mark of the diffraction grating form from different directions;
said photodetector comprises first and second photodetectors,
wherein: the first photodetector is to receive first interference
light comprised of multiple diffraction light generating in a
direction parallel to a first direction from the mark of the
diffraction grating form; and the second photodetector is to
receive second interference light comprised of multiple diffraction
light generating in a direction parallel to a second direction yet
different from the first direction from the mark of the diffraction
grating form; and said optical guide comprises two optical guides
for leading said first and second diffraction light independently
from each other to the respective photodetectors.
5. A position transducer as claimed in any one of claims 1 to 4,
wherein: said light flux for position detection comprises light
flux of multiple wavelengths; and the light flux of multiple
wavelengths is led to said illumination optical system via multiple
optical guides different for each wavelength.
6. A position transducer as claimed in any one of claims 1 to 5,
wherein: said first interference light comprised of multiple
diffraction light generating in the direction parallel to the first
direction from the mark of the diffraction grating form is led to
said first photodetector via said optical guide after separation
into each of the wavelengths of the light flux; and said second
interference light comprised of multiple diffraction light
generating in the direction parallel to the second direction yet
different from the first direction from the mark of the diffraction
grating form is led to said second photodetector via said optical
guide after separation into each of the wavelengths of the light
flux.
7. A position transducer as claimed in any one of claims 1 to 5,
wherein: said first interference light comprised of multiple
diffraction light generating in the direction parallel to the first
direction from the mark of the diffraction grating form is led to a
position in the vicinity of said first photodetector via said
optical guide before separation into each of the wavelengths of the
light flux; and said second interference light comprised of
multiple diffraction light generating in the direction parallel to
the second direction yet different from the first direction from
the mark of the diffraction grating form is led to a position in
the vicinity of said second photodetector via said optical guide
before separation into each of the wavelengths of the light
flux.
8. An exposure apparatus for transcribing a mask pattern on a
photosensitizable substrate, having a position transducer as
claimed in any one of claims 1 to 7, wherein: said mark for
position detection on said photosensitizable substrate is detected
given by said position transducer as a mark for position detection
on the substrate to be detected; and said photosensitizable
substrate is aligned on the basis of a result of detection given by
said position transducer.
9. An exposure apparatus having a main body portion for
transcribing a mask pattern on a photosensitizable substrate and a
position detection system for detecting a position of a mark for
position detection formed on said photosensitizable substrate and
having said main body portion and said position detection system
arranged so as to align said mask pattern with said
photosensitizable substrate on the basis of a result of detection
of a position of said mask pattern detected by said position
detection system; wherein: said position detection system comprises
a laser light source for generating laser light with multiple
wavelengths, an illumination optical system for illuminating the
laser light from said laser light source onto the mark for position
detection formed on said photosensitizable substrate, and a light
recipient optical system for receiving light returning from said
mark for position detection; and said laser light source is
isolated from said main body portion of said exposure
apparatus.
10. An exposure apparatus as claimed in claim 9, wherein the laser
light of multiple wavelength from said laser light source is led to
said illumination optical system through the optical guides
different for each wavelength.
11. An exposure apparatus as claimed in claim 9 or 10, wherein said
light recipient optical system is to receive diffraction light
generated in a predetermined direction by said laser light from
said mark for position detection.
12. An exposure apparatus as claimed in claim 8, wherein: said
illumination optical system is to illuminate said laser light of
multiple wavelengths on a mark of a linear dot arrangement as said
mark for position detection and to detect a position of the mark of
the linear dot arrangement on the basis of a light amount of the
diffraction light to be received by said light recipient optical
system.
13. An exposure apparatus comprising: a main body portion having an
illumination optical system and arranged to transcribe a mask
pattern of a reticle on a wafer by light for exposure generating
from said illumination optical system; an alignment optical system
for illuminating a light flux for alignment comprised of multiple
light fluxes having different wavelengths on a mark for position
detection provided on each of said reticle and said wafer; a first
photomultiplier for receiving diffraction light of said light flux
for alignment from said mark for position detection of said
reticle; a second photomultiplier for receiving diffraction light
of said light flux for alignment from said mark for position
detection of said wafer; a phase difference detector for detecting
a phase difference between said reticle and said wafer on the basis
of electrical signals converted photoelectrically by said first and
second photomultipliers; an alignment device for aligning said
reticle with said wafer on the basis of the phase difference
detected by said phase difference detector; and an optical guide
for leading each of the diffraction light from said mark for
position detection of said reticle and the diffraction light from
said mark for position detection of said wafer to said respective
first and second photomultipliers.
14. An exposure apparatus as claimed in claim 13, wherein: the
diffraction light from each of said marks for position detection of
said reticle and said wafer comprises a light flux of multiple
wavelengths; and the light flux returning from each of said marks
for position detection of said reticle and said wafer is led to
said photomultiplier through the optical guide different for each
wavelength after separation into each wavelength.
15. An exposure apparatus as claimed in claim 14, wherein: each of
said multiple optical guides comprises an optical fiber with a
propagation efficiency optimized for a wavelength of the light flux
as an object of propagation.
16. An exposure apparatus as claimed in any one of claims 13 to 15,
wherein: said mark for position detection is a mark of a
diffraction grating form arranged by a predetermined pitch in a
direction of measurement; and said alignment optical system is an
optical system for illuminating mutually coherent multiple light
fluxes onto said mark of the diffraction grating form from
different directions.
17. An exposure apparatus as claimed in any one of claims 13 to 16,
wherein: said light flux for alignment comprises a light flux of
multiple wavelengths; and said light flux is led to said alignment
optical system through an optical guide different for each of the
multiple wavelengths constituting the light flux.
18. An exposure apparatus as claimed in claim 16 or 17, wherein:
said first interference light comprised of multiple diffraction
light generating from said mark of the diffraction grating form in
a direction parallel to a first direction is led to said first
photomultiplier by said optical guide after separation into a light
flux of each wavelength; and said second interference light
comprised of multiple diffraction light generating from said mark
of the diffraction grating form in a direction parallel to a second
direction yet different from the first direction is led to said
second photomultiplier by said optical guide after separation into
a light flux of each wavelength.
19. An exposure apparatus as claimed in claim 16 or 17, wherein:
said first interference light comprised of multiple diffraction
light generating from said mark of the diffraction grating form in
a direction parallel to a first direction is led to a position in
the vicinity of said first photomultiplier by said optical guide
before separation into a light flux of each wavelength; and said
second interference light comprised of multiple diffraction light
generating from said mark of the diffraction grating form in a
direction parallel to a second direction yet different from the
first direction is led to a position in the vicinity of said second
photomultiplier by said optical guide before separation into a
light flux of each wavelength.
20. An exposure apparatus as claimed in claim 9, wherein: said
light recipient optical system contains a light recipient element
for photoelectrically converting the light returning from said mark
for alignment; and said light recipient element is disposed in a
position isolated from the main body portion of the exposure
apparatus.
21. A method for detecting a position of a substrate, comprising:
illuminating multiple pairs of light for position detection onto a
mark formed on the substrate from two different directions;
receiving the light from the mark by a light recipient element;
detecting the position of the substrate on the basis of optical
information from said light recipient element; and leading the
multiple pairs of the light for position detection to the substrate
through an optical guide.
22. A method as claimed in claim 21, wherein: the light from said
mark is led to said light recipient element through a guide.
23. A method for exposing a mask pattern to a substrate,
comprising: illuminating different rays of light for position
detection onto a mark formed on said substrate; receiving the light
from the mark by a light recipient element; detecting the position
of the substrate on the basis of optical information from said
light recipient element; and leading the light for position
detection to the substrate from outside of a chamber with said
substrate disposed therein.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a position transducer and
an exposure apparatus with the same and, more particularly, to a
position transducer and an exposure apparatus with the same, a
position transducer being suitable for use with an alignment sensor
for an exposure apparatus for exposing a pattern on a mask to a
photosensitizable substrate in a photolithographic step for
manufacturing semiconductor elements, liquid crystal display
elements, image pick-up tubes (CCDs etc.), thin layer magnetic
heads and so on.
[0002] In a photolithographic step for manufacturing semiconductor
elements and so on, there has hitherto been frequently employed a
so-called stepper for exposing and transcribing a pattern of a
reticle as a mask on each shot area on a photosensitizable
substrate, such as a wafer, a glass plate or the like, by a
step-and-repeat exposure system as an exposure apparatus to be
employed for exposing and transcribing a pattern of a reticle
acting as a mask onto such a photosensitizable substrate with a
photoresist layer coated thereon.
[0003] Recently, there is being employed an exposure apparatus of a
scanning exposure type, for example, of a step-and-scan system
comprising exposing a reticle to a wafer while scanning the reticle
and the wafer in synchronization with a projection optical system.
Such exposure apparatuses require a particularly high level of
precision in alignment of the reticle with each shot area on the
wafer due to the fact that multiple layers of circuit patterns are
superimposed on the wafer in manufacturing semiconductor elements
and so on. Therefore, alignment sensors of various types and
systems are employed for such exposure apparatuses.
[0004] Among conventional alignment sensors, an alignment sensor of
a so-called grating alignment method uses laser beams as a source
of alignment and a wafer mark in the form of a grating with its
bars or dots arranged periodically. This grating alignment method
may be classified by the structure of an alignment optical system
or a detection system, a number of alignment beams of light and so
on. The grating alignment method may further be broken down into
the following types.
[0005] A first type of the grating alignment method is of the type
comprising allowing one laser beam to strike the whole area of a
wafer mark on a wafer, causing two rays of diffraction light
generated from the wafer mark to form an image on a reference
grating, scanning the wafer mark relative to the reference grating,
and detecting the position of the wafer mark on the basis of a
variation with a quantity of light transmitted through the
reference grating or reflected therefrom.
[0006] A second type of the grating alignment method is of the type
comprising allowing two laser beams to strike the whole area of a
wafer mark on a wafer from the particular yet mutually different
directions of the diffraction order and detecting the position of
the wafer mark on the basis of the phase of interference light
generating in the identical direction from the wafer mark. This is
called as an LIA (Laser Interferometric Alignment) type.
[0007] The LIA type may be classified into two groups, one group
being of a homodyne interference type transferring a wafer mark
relative to a static interference fringe formed by two laser beams
having no frequency difference and the other being of a heterodyne
interference type measuring a phase difference between a signal
photoelectrically detecting an interference light (beat light) of
two diffraction light components generated from the wafer mark by
two laser beams having a slight difference of frequencies
therebetween and a reference signal having the same frequency as
the frequency difference between the two laser beams and detecting
the phase difference as an amount of a pitch-directional deviation
of the position of the wafer mark of the grating form from the
predetermined reference point.
[0008] Where the diffraction light generated from the
grating-shaped wafer mark is detected as a signal using a source of
monochromatic light in the manner as described hereinabove, the
shape of the grating wafer mark may become non-symmetric as
multiple thin layers are superimposed on a wafer substrate more and
more, or no diffraction light to be detected may be generated for
laser beams of certain wavelengths striking the wafer mark due to
interference of a thin layer of the surface photoresist coating or
for other reasons, or errors in detecting the diffraction light may
be caused to occur due to a very faint intensity of the diffraction
light generated therefrom. In order to solve those problems and to
enable a more accurate detection of the position of the wafer mark,
there has been developed an alignment sensor of a heterodyne
interference type using a source of polychromatic light having
multiple wavelengths.
[0009] An alignment sensor of a heterodyne interference type using
a light flux with multiple wavelengths is constructed so as to
allow two laser beams having different wavelengths to strike the
wafer mark of a wafer from a direction of a particular order after
the two laser beams with different wavelengths are modified to
provide a slight difference in frequency therebetween and to
photoelectrically detect the interference light consisting of the
multiple wavelength components generated therefrom. The diffraction
light of each wavelength component is photoelectrically detected in
the form in which it is summed up altogether on a light recipient
surface of a photoelectrical detection element, as an example, so
that the detection of the position of the wafer mark may be less
affected by an influence of interference of the thin layer on the
photoresist coating or a deviation of the diffraction light due to
an influence of non-symmetric shape between the sectional shapes of
the wafer mark.
[0010] Further, there is another method of detecting diffraction
light using an alignment sensor of a system referred to as an LSA
(Laser Step Alignment) system, like the grating alignment system,
which comprises forming a laser spot on the wafer by converging one
laser beam thereonto, scanning the laser spot relative to the wafer
with a wafer mark with dots arranged linearly thereon through a
wafer stage, and detecting the position of the wafer mark on the
basis of the intensity of diffraction light generated upon passage
through the wafer mark beneath the laser spot.
[0011] For such conventional alignment sensors, a photomultiplier
is employed as a photodetector when a sensitivity of light for
detection from the wafer mark is required to be enhanced. Such a
photomultiplier, however, may become a cause to induce a variation
in temperature or a temperature gradient in the atmosphere
surrounding it because it generates heat upon operation in
progress. On the other hand, hitherto, the alignment sensor has
been provided in the vicinity of an exposing main body portion of
an exposure apparatus with the object of making the exposure
apparatus compact. There is a risk, accordingly, that the exposing
main body portion thereof and the wafer as a recipient that is
exposed to light undergo thermal expansion or other transformation,
causing faults and irregularities in accuracy of alignment and of
exposure to light (accuracy of superimposition). In addition, as a
photomultiplier is usually large in size, it is difficult in terms
of making the exposure apparatus compact in size as a whole to
locate such a photomultiplier nearby the exposing main body portion
thereof.
[0012] Furthermore, even when there are some cases where a
photodiode or the like is employed as a photodetector, a
preamplifier and other means provided on such a photodetector may
also become a source of generating heat. Where the photodetector
generates heat, the heat may cause turbulence of the air
surrounding it, resulting in disturbance of the light to be
employed for the detection of alignment. This of course may
adversely affect the accuracy in the detection of the wafer mark on
the wafer.
[0013] Particularly, when a source of light having multiple
wavelengths is employed for alignment, there are cases in some
uses, where such light of different wavelengths is required to be
received for detection by different photodetectors. In this case,
the number of the photodetectors increases so that the amount of
heat generated by them becomes larger leading to the larger
possibility of inducing faults and irregularities in precision of
exposure. In addition, the source of light for alignment may
adversely affect precision in exposure as a source of generating
heat, like photodetectors.
SUMMARY OF THE INVENTION
[0014] Therefore, the present invention has a primary object of
providing a position transducer that does not substantially exert
an influence of heat upon a substrate to be subjected to
detection.
[0015] The present invention has another object of providing a
position transducer constructed so as to separate a heat source
from the exposure apparatus in order to fail to cause the heat
generated from the heat source to exert an adverse influence upon a
substrate to be subjected to detection.
[0016] The present invention has a further object of providing a
position transducer that does not or little undergo an adverse
influence upon such a substrate due to turbulence of air within the
exposure apparatus or for other reasons.
[0017] The present invention has a still further object of
providing a position transducer that can reduce or minimize an
adverse influence to be otherwise exerted upon such a substrate by
the generation of heat from a photodetector when such a
photodetector having a large calorific power is employed.
[0018] The present invention has another still further object of
providing a position transducer that can reduce an adverse
influence upon such a substrate and enables the detection of a
position of the substrate with a high degree of precision, even if
a light flux of multiple wavelengths is employed as a light flux
for position detection.
[0019] The present invention has another still further object of
providing an exposure apparatus with such a position transducer
disposed therewith, particularly to provide an exposure apparatus
capable of excluding an influence from the heat generated from the
light for alignment even when there is employed a light source for
alignment of a large calorific power, like a light source having
multiple wavelengths.
[0020] In addition, the present invention has still another object
of providing an exposure apparatus with such a position transducer,
which does not cause any decrease in precision of alignment even if
an optical fiber or the like is employed upon alignment using a
light flux of multiple wavelengths.
[0021] In order to achieve the objects as described hereinabove,
the position transducer according to the present invention is
constructed from an illumination optical system for illuminating a
light flux for position detection onto a mark for position
detection formed on a substrate to be detected, and from a
photodetector for receiving the light flux returned from the mark
for position detection so as to detect the position of the
substrate on the basis of a signal converted photoelectrically by
the photodetector, wherein an optical guide is provided for leading
the light flux returned from the mark for position detection to the
photodetector.
[0022] With the arrangement of the position transducer according to
the present invention, the substrate to be detected and the
exposing main body portion of the exposure apparatus can be
separated and isolated from the photodetector acting as the heat
source by transmitting the light flux returning from the mark for
position detection via the optical guide, thereby excluding such
factors as exert an adverse influence upon the detection of the
position with high precision, such as thermal expansion or the
like.
[0023] Further, the arrangement of the position transducer
according to the present invention can serve to improve the
precision of position detection because the light flux is
transmitted to the photodetector via the optical guide and there
can be employed a light flux that does not undergo any influence by
turbulence of the air surrounding the photodetector.
[0024] In this case, it can be taken as an example that,
preferably, the light flux for position detection comprises a light
flux of multiple wavelengths and the light flux to be returned from
the mark for position detection to the photodetector is led for
each wavelength through a different optical guide to the
photodetector. With this arrangement, an influence of the heat
generated from the photodetector can be alleviated or decreased as
compared with the instance where light fluxes each of multiple
wavelengths are received by the respective photodetectors.
[0025] Further, it is preferred that there is employed, as the
optical guide, an optical fiber being so adapted as to have its
propagation efficiency optimized to the wavelength of the light
flux as an object of propagation. The use of such an optical fiber
enables the transmission of the light flux of multiple wavelengths
at their respectively minimized attenuation ratios, thereby
providing, for example, a signal for position detection for each
wavelength accurately at an equal SN ratio.
[0026] It is additionally preferred that, when the mark for
position detection comprises a mark of a diffraction grating form
with dots, bars etc. arranged each by a predetermined pitch in the
direction of measurement, for example, as shown in FIG. 7, the
illumination optical system is constructed by an optical system for
illuminating mutually coherent multiple light fluxes as the light
flux for position detection from different directions onto the mark
of the diffraction grating form, and the photodetector comprises a
first photodetector and a second photodetector with each optical
guide disposed so as to lead first and second diffraction light
separately or independently from each other to the first and second
photodetectors, respectively, the first photodetector being
arranged so as to receive the first diffraction light consisting of
multiple rays of diffraction light generating in a direction
parallel to a first direction from the mark of the diffraction
grating form, and the second photodetector arranged so as to
receive the second diffraction light consisting of multiple rays of
diffraction light generating in a direction parallel to a second
direction yet different from the first direction from the mark of
the diffraction grating form. This construction allows two
different kinds of interference light generating in the different
directions to be detected independently and separately from each
other.
[0027] It is furthermore preferred that, when the light flux for
position detection comprises a light flux of multiple wavelengths,
the light flux of the multiple wavelengths is led for each
wavelength to the corresponding illumination optical system through
each of the plural optical guides. The manner of transmission of
the light flux of each wavelength via each of the mutual optical
guides can reduce such an influence to be otherwise exerted by the
generation of heat from the light flux for position detection.
[0028] Further, the exposure apparatus according to the present
invention comprises an exposing main body portion for transcribing
a mask pattern on a photosensitizable substrate and a position
detection system for detecting a mark of position alignment formed
on the photosensitizable substrate, which are constructed in such a
manner that the mask pattern is aligned with the photosensitizable
substrate on the basis of a result of detection by the position
detection system. In the arrangement of the exposure apparatus as
described hereinabove, the position detection system comprises a
laser light source for generating laser light of multiple
wavelengths, an illumination optical system for illuminating the
laser light from the laser light source onto the mark for position
detection on the photosensitizable substrate, and a light recipient
optical system for receiving the light returned from the mark for
position detection, the laser light source being disposed separated
or isolated from the exposing main body portion of the exposure
apparatus. The manner of separating or isolating the laser light
source from the exposing main body portion thereof may include, for
example, accommodating either of them in a discrete chamber or
accommodating both of them with a portion thereof air-conditioned
forcibly.
[0029] By separating or isolating the laser light source generating
laser light of multiple wavelengths, which acts as a heat source in
the position detection system, from the exposing main body portion,
adverse influences upon the exposing main body portion and the
photosensitizable substrate, which may be otherwise exerted by the
heat generated from the laser light source, can be excluded.
Further, by implementing alignment using laser light of multiple
wavelengths, alignment of a high degree of precision can be
achieved without any great interference among thin layers of a
photosensitizable substrate or a shape of the mark for position
detection.
[0030] In this case, the exposure apparatus is preferably arranged
such that laser light of multiple wavelengths from the laser light
source is led to the illumination optical system through a
different optical guide for each wavelength. Further, at this time,
it is possible to use an optical guide, such as an optical fiber,
with its transmission efficiency optimized for each of the
wavelengths, so that laser light of multiple wavelengths can be
utilized effectively. Further, by synthesizing laser light of
multiple wavelengths in the vicinity of the exposing main body
portion of the exposure apparatus, the position of the mark for
position detection can be detected with high precision.
[0031] In accordance with the position transducer and the exposure
apparatus according to the present invention, the light recipient
optical system is so arranged as to receive, for example,
diffraction light generated by the laser light from the mark for
position detection in the predetermined direction. This means that
the present invention is applied to an exposure apparatus utilizing
the alignment system of the grating alignment method or of the LSA
method.
[0032] In this case, further, the illumination optical system may
be so arranged as to illuminate the laser light of multiple
wavelengths onto a comfrising mark dots arranged linearly for
position detection, and the position of the mark linear dot is to
be detected on the basis of an amount of diffraction light received
by the light recipient optical system. This means that there is
employed an alignment system of the LSA method in which the light
flux is of multiple wavelengths.
[0033] Other objects, features and advantages of the subject
invention will become apparent in the course of the following
description with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 is a block diagram showing an exposure apparatus with
a position transducer according to a first embodiment of the
present invention.
[0035] FIG. 2 is a schematic structural diagram showing an
alignment optical system 9 and a main body portion 8 of FIG. 1.
[0036] FIG. 3(a) is an enlarged plan view showing a reticle mark RM
on a reticle 1 of FIG. 2.
[0037] FIG. 3(b) is an enlarged plan view showing a wafer mark WM
on a wafer 4.
[0038] FIG. 4(a) is an enlarged plan view showing a field diaphragm
34 of FIG. 2.
[0039] FIG. 4(b) is an enlarged plan view showing a field diaphragm
31.
[0040] FIG. 5(a) is a schematic view illustrating the principle of
creating two light fluxes (two light fluxes having frequencies
different from each other) of AOM 17A AND 17B of FIG. 2.
[0041] FIG. 5(b) is a schematic view showing the state in which
FIG. 5(a) converts to multiple wavelengths.
[0042] FIG. 6 is a schematic view showing the state in which
diffraction light is generated at the wafer mark WM provided on the
wafer 4.
[0043] FIG. 7 is a view illustrating the principle of detection in
a second embodiment of the position transducer according to the
present invention.
[0044] FIG. 8 is a schematic view of the essential portion of a
light recipient system in a third embodiment of the position
transducer according to the present invention.
[0045] FIG. 9 is a view showing the construction of a projection
exposure apparatus with an alignment system of the LIA method as a
second embodiment of the exposure apparatus according to the
present invention.
[0046] FIG. 10 is an enlarged view showing laser beams illuminated
onto wafer mark 3Y of FIG. 9 and diffraction light of the laser
beams from the wafer mark 3Y.
[0047] FIG. 11 is a view showing the construction of the exposure
apparatus in a third embodiment of the present invention.
[0048] FIG. 12 is a view showing the construction of the exposure
apparatus in a fourth embodiment of the present invention.
[0049] FIG. 13 is a plan view showing wafer marks 3XA and 3YA on a
wafer W of FIG. 12 and laser beams LB3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0050] First Embodiment
[0051] The exposure apparatus in the first embodiment according to
the present invention will be described with reference to FIGS. 1
to 6. This embodiment of the exposure apparatus is of the type in
which the present invention is applied to a projection exposure
apparatus of a stepper type with an alignment sensor of the LIA
system. The alignment sensor to be employed in this embodiment is
arranged so as to adapt to multiple wavelengths.
[0052] FIG. 1 is a block diagram showing the projection exposure
apparatus according to the first embodiment of the present
invention. In FIG. 1, as a light source for use in alignment, there
are employed three different light sources 10A, 10B and 10C, each
consisting of a laser diode capable of generating laser beams
having wavelengths .lambda.A, .lambda.B and .lambda.C,
respectively. More specifically, the first light source 10A
generates laser beams having the wavelength .lambda.A (hereinafter
referred to from time to time as "light flux LA"), the second light
source generates laser beams having the wavelength .lambda.B
(hereinafter referred to from time to time as "light flux LB"), and
the first light source 10C. generates laser beams having the
wavelength .lambda.C (hereinafter referred to from time to time as
"light flux LC"). As an example, the wavelengths .lambda.A,
.lambda.B and .lambda.C may be set as 635 nm, as 690 nm and as 780
nm, respectively. Further, the light fluxes LA-LC, inclusive, may
be polarized linearly.
[0053] In the first embodiment, there may be employed optical
fibers 11A, 11B and 11C, each having the characteristic for holding
a plane of polarization with its propagation efficiency optimized
to each of the wavelengths .lambda.A, .lambda.B and .lambda.C,
respectively. The light fluxes LA, LB and LC generated as light for
alignment from the first, second and third light sources 10A, 10B
and 10C are transmitted to an alignment optical system 9,
respectively, via the optical fibers 11A, 11B and 11C with each of
the propagation efficiency optimized to each of the respective
wavelengths .lambda.A, .lambda.B and .lambda.C.
[0054] FIG. 2 illustrates the construction of the alignment optical
system 9 and the exposing main body portion 8 of the projection
exposure apparatus in the first embodiment of the present
invention. As shown in FIG. 2, a reticle 1 is provided with a
circuit pattern of a predetermined shape and with a reticle mark RM
of a diffraction grating form at a peripheral portion around the
pattern as a mark for alignment. The reticle 1 is held on a reticle
stage 2 disposed so as to be movable in two dimensions and it is
located thereon so as to be conjugated with a wafer 4 with respect
to a projection optical system (projection objective lens) 3. In
the following description, the direction parallel to the optical
axis of the projection optical system 3 is set as a z-axis, the
direction on the plane perpendicular to the z-axis and parallel to
the paper surface of FIG. 1 is set as an x-axis, and the direction
perpendicular to the paper surface of FIG. 1 is set as a
y-axis.
[0055] The light from an illumination optical system 40 for use in
exposing the circuit pattern on the reticle 1 onto the wafer 4 is
so arranged as to reflect downwards by a dichroic mirror 6 arranged
so as to be directed upwardly at an angle of inclination of
45.degree. with respect to the z-axis and to illuminate the reticle
1 at a uniform degree of illuminance. Upon exposure to the light
from the illumination optical system 40, the pattern on the reticle
1 is transcribed on each of shot areas on the wafer 4 by the
projection optical system 3. The wafer 4 is provided in each of the
short areas with a wafer mark WM of a diffraction grating shape for
use in alignment, in substantially the same manner as the reticle
mark RM formed on the reticle 1.
[0056] The wafer 4 is held on a wafer stage 5 so as to be movable
in two-dimensions, i.e. x-axial and y-axial directions, in a
step-and-repeat system. As the reticle pattern has been transcribed
on one of the shot areas on the wafer 4, the wafer is moved in a
stepwise manner to the next shot area. In order to allow the
discrete detection of the position of the wafer 4 in the direction
of rotation (.theta.) on the plane in the x-axial and y-axial
directions and in the xy-axial direction in the reticle stage 2 and
the wafer stage 5, each stage is provided with an interferometer,
although not shown, that can discretely detect the position in the
direction of rotation (.theta.) in the x-axial and y-axial
directions and in the x-axial and y-axial plane in the reticle
stage 2 and the wafer stage 5. Further, each stage can be driven in
each of the directions by a driving motor, although not shown.
[0057] On the other hand, the alignment optical system 9 for
detecting the position of the reticle mark RM and the wafer mark WM
is provided over a dichroic mirror 6.
[0058] Now, description will be made of the alignment optical
system 9 with reference to FIG. 2.
[0059] In the alignment optical system 9, the light fluxes LA and
LB led from the optical fibers 11A and 11B are collimated by the
lenses 12A and 12B, respectively, and they strike the dichroic
mirror 13A with the plane of reflection disposed at the angle of
inclination of 45.degree. relative to the z-axis. As the dichroic
mirror 13A has the characteristic of selecting the wavelength that
transmits the light flux having the wavelength .lambda.A and
reflects the light flux having the wavelength .lambda.B, the light
fluxes LA and LB strike the dichroic mirror 13B with their planes
of polarization sustained and their optical axes united. The light
flux LC led from the optical fiber 11C is also arranged to strike
the dichroic mirror 13B with its plane of reflection disposed at
the angle of inclination of 45.degree. with respect to the z-axis
after it has been collimated by the lens 13C. The dichroic mirror
13C has the characteristic of selecting the wavelengths so as to
allow the light fluxes having the wavelengths .lambda.A and
.lambda.B to pass therethrough and the light flux having the
wavelength .lambda.C to reflect therefrom. Hence, the light fluxes
LA, LB and LC are converted to combined light (hereinafter referred
to as "light flux LI") with their polarized planes retained and
with their optical axes united together and then transmitted to a
first audio optical element (hereinafter referred to as "AOM") 17A
in a nearly perpendicular direction. A second AOM 17B is disposed
apart in a predetermined distance s behind the first AOM 17A. The
first AOM 17A is driven in the reverse direction by high frequency
signals SF.sub.1 having a frequency f.sub.1, and the second AOM 17B
is driven in the reverse direction by high frequency signals
SF.sub.2 having a frequency f.sub.2. In this case, the first
frequency f.sub.1 is set to be larger than the second frequency
f.sub.2. Hence, the light flux LI consisting of the light fluxes
LA, LB and LC with the respectively predetermined wavelengths
.lambda.A, .lambda.B and .lambda.C undergoes the Raman-Nath
diffraction action by the AOMs 17A and 17B.
[0060] In the following description, the order of diffraction light
is considered on the basis of the direction in which the wave of
the high frequency SF.sub.1 advances.
[0061] A combined light (hereinafter referred to as "L.sub.1(1)")
of plus first-order diffraction light of the light flux LI from
each of the two AOMs 17A and 17B substantially undergoes modulation
of frequency by (f.sub.1-f.sub.2)/2 by the two AOMs. Likewise,
another combined light (hereinafter referred to as "L.sub.2(-1)")
of minus first-order diffraction light of the light flux LI from
the two AOMs 17A and 17B substantially undergoes modulation of
frequency by (f.sub.1-f.sub.2)/2 by the two AOMs.
[0062] Thereafter, the combined light fluxes L.sub.1(1) and
L.sub.2(-1) allow their light paths to be turned to minus (-)
z-axial direction by a mirror 22 through a lens 18a, a reflecting
mirror 20 and lenses 18b and 21. Between the lenses 18a and 18b
constituting a relay optical system is provided a space filter 19
for extracting the light fluxes L.sub.1(1) and the light flux
L.sub.2(-1). Although diffraction light of zero order or higher
orders of the light flux LI is generated from the AOMs 17A and 17B,
the space filter 19 blocks the passage of the such diffraction
light, allowing only the diffraction light of plus and minus
first-order to transmit therethrough. Between the lenses 18a and
18b is interposed a field diaphragm 57.
[0063] The light fluxes L.sub.1(1) and L.sub.2(-1) with their light
paths turned in the minus (-) z-axial direction by the mirror 22
are then allowed to be transmitted to relay optical systems 26a,
26b and 27, a beam splitter 28 and a plane parallel plate 37. The
plane parallel plate 37 is disposed at a position at which the
pupil surfaces of the projection optical system 3 are conjugated or
in its vicinity thereof so as to be variable in an angle of
inclination with respect to the optical axis of the alignment
optical system and has the function of sustaining telecentricity. A
combination of a thick plane parallel plate for rough adjustment
with a thin plane parallel plate for minute adjustment may also be
employed, in place of the plane parallel plate 37.
[0064] The light fluxes L.sub.1(1) and L.sub.2(-1) passing through
the plane parallel plate 37 illuminates the reticle mark RM of the
diffraction grating form on the reticle 1 from two directions at a
predetermined intersecting angle through the objective lens 38 and
the dichroic mirror 6.
[0065] In cases where the projection optical system 3 is not
corrected of chromatic aberration with respect to the light for
alignment, it is preferred that the objective lens 38 is
constructed from a bi-focal optical system as proposed in Japanese
Patent Unexamined Publication No. 63-283,129. This construction can
divide each of the two light fluxes entered into the bifocal
optical system into two rays of polarized light, which intersect at
right angles to each other, both of the one rays of the polarized
light directing to the first focus being converged onto the reticle
1 and both of the other rays thereof directing to the second focus
being converged onto the wafer 4.
[0066] As described hereinabove, the light fluxes L.sub.1(1) and
L.sub.2(-1) illuminate the reticle mark RM on the reticle 1. The
reticle 1 has a window P.sub.0, through which to pass the light for
alignment, disposed in alignment with the reticle mark RM, as shown
in FIG. 3(a), and the wafer mark WM of the diffraction grating form
is provided on the wafer 4 in the position corresponding to the
window P.sub.0, as shown in FIG. 3(b).
[0067] The light fluxes L.sub.1(1) and L.sub.2(-1) illuminate the
reticle mark RM and the window P.sub.0 so as to cover them from two
directions, thereby generating interference fringes extending along
the pitch direction on the reticle mark RM. Further, the minus
first-order diffraction light of the light flux L.sub.1(1) and the
plus first-order diffraction light of the light flux L.sub.2(-1)
are each generated in the normal direction (plus z-axial direction)
of the reticle mark RM.
[0068] In the following description of this specification, a
mixture of the minus first-order diffraction light of the light
flux L.sub.1(1) and the plus first-order diffraction light of the
light flux L.sub.2(-1) generated at the reticle mark RM is referred
to as "light flux LR"; the component having wavelength .lambda.A in
the light flux LR is referred to as "light flux LAR"; the component
having wavelength .lambda.B in the light flux LR is referred to as
"light flux LBR"; and the component having wavelength .lambda.C in
the light flux LR is referred to as "light flux LCR".
[0069] The angles at which the light flux L.sub.1(1) intersects the
light flux L.sub.2(-1) when illuminating the reticle mark RM from
two directions are set so as to satisfy the following relationship
(1):
sin .theta..sub.RM=.lambda..sub.0/P.sub.RM (1)
[0070] where
[0071] .theta..sub.RM is the angle at which the light flux
L.sub.1(1) or L.sub.2(-1) strikes the reticle mark RM;
[0072] P.sub.RM is the pitch of the reticle mark RM; and
[0073] .lambda..sub.0 is the wavelength .lambda.A, .lambda.B or
.lambda.C.
[0074] In this case, the angle .theta..sub.RM at which the light
flux L.sub.1(1) or L.sub.2(-1) enters is set so as to vary with
wavelength.
[0075] This construction can generate the light flux LR from the
reticle mark RM in the direction perpendicular to the +z-axial
direction. Thereafter, the light flux LR generated from the reticle
mark RM is allowed to pass through the dichroic mirror 6, the
objective lens 38 and the parallel plane plate 37, and it is then
reflected at the beam splitter 28 and transmitted to the field
diaphragm 34 through the lens 29 and the beam splitter 30.
[0076] The field diaphragm 34 is disposed in the position in which
it conjugates with the reticle 1. Specifically, as indicated by the
oblique lines in FIG. 4(a), the field diaphragm 34 is provided with
an opening portion SRM in the position corresponding to the
position of the reticle mark RM in order to allow a passage of only
the diffraction light from the reticle mark RM of the reticle
1.
[0077] The diffraction light from the reticle mark RM passed
through the field diaphragm 34 is subjected to filtering by a space
filter 35 that can block the passage of the zero-order diffraction
light, thereby causing the light path of the light flux LR only to
be turned by the dichroic mirror 47C. The light flux LR is then
allowed to strike the dichroic mirror 47B and then the dichroic
mirror 47A. The dichroic mirror 47B has the characteristic of
selecting wavelengths to reflect only the light flux LCR having the
wavelength .lambda.C in the light flux LR generated from the
reticle mark RM of the reticle 1 and to allow the rest of the light
fluxes LAR and LBR to pass therethrough. The light flux LCR
reflected at the dichroic mirror 47B is collimated with the lens
48C, followed by introduction into an optical fiber 49C in which
the propagation efficiency has been optimized to the wavelength
.lambda.C. Then, the light flux LCR is transmitted through the
optical fiber 49C and reaches the photomultiplier 51C acting as a
photodetector, as shown in FIG. 1, which in turn can
photoelectrically detect the optical beat signals having a
frequency (f.sub.1-f.sub.2) and containing information on the
position of the reticle 1. The signals generated from the
photomultiplier 51C is supplied through a low-path filter circuit
(not shown) capable of passing signals having a frequency of
approximately f.sub.1/2 to a phase detection comparison system 43
as reticle beat signals SRC. As an example, the frequencies f.sub.1
and f.sub.2 may be set to be several 10 MHz and the frequency
(f.sub.1-f.sub.2) may be set to be several 10 KHz.
[0078] On the other hand, as shown in FIG. 2, the light fluxes LAR
and LBR which passed through the dichroic mirror 47B enter into the
dichroic mirror 47A. The dichroic mirror 47A in turn has the
characteristic for selecting the wavelengths such that the light
flux LBR with the wavelength .lambda.B is reflected thereby and
that the light flux LAR with the wavelength .lambda.A is allowed to
pass therethrough. The light flux LBR reflected by the dichroic
mirror 47A is collimated by the lens 48B and it is then introduced
into an optical fiber 49B with its propagation efficiency optimized
to the wavelength .lambda.B, followed by transmission to a
photomultiplier 51B, as shown in FIG. 1. The light flux LBR
transmitted thereto is then processed in the same manner as the
light flux LCR as described hereinabove to generate reticle beat
signals SRB. On the other hand, the light flux LAR which also
passed through the dichroic mirror 47A is collimated by the lens
48A and introduced into an optical fiber 49A with its propagation
efficiency optimized to the wavelength .lambda.A, followed by
transmitting to a photomultiplier 51A of FIG. 1 and generating
reticle beat signals SRA in substantially the same manner as the
light fluxes LBR and LCR.
[0079] Furthermore, as shown in FIG. 2, a portion of the light
fluxes L.sub.1(1) and L.sub.2(-1) passed through the window P.sub.0
of the reticle 1 illuminates the wafer mark WM of a diffraction
grating form on the wafer 4 through the projection optical system 3
from two directions at a predetermined angle at which the light
fluxes intersect with each other, thereby enabling a formation of
interference fringes extending in the pitch direction on the wafer
mark WM. Further, the minus first-order diffraction light of the
light flux L.sub.1(1) and the plus first-order diffraction light of
the light flux L.sub.2(1) are generated in the direction of the
normal of the wafer mark WM.
[0080] It is to be understood herein that a mixture of the minus
first-order diffraction light of the light flux L.sub.1(1) and the
plus first-order diffraction light of the light flux L.sub.2(-1)
generated at the wafer mark WM is referred to as "light flux LW";
the component having wavelength .lambda.A in the light flux LW is
referred to as "light flux LAW"; the component having wavelength
.lambda.B in the light flux LW is referred to as "light flux LBW";
and the component having wavelength .lambda.C in the light flux LW
is referred to as "light flux LCW".
[0081] The angles at which the light fluxes L.sub.1(1) and
L.sub.2(-1) illuminate the wafer mark WM from two directions are
set so as to satisfy the following relationship:
sin .theta..sub.WM=c/P.sub.WM (2)
[0082] where
[0083] .theta..sub.WM is the angle at which the light flux
L.sub.1(1) or L.sub.2(-1) strikes the wafer mark WM;
[0084] P.sub.WM is the pitch of the wafer mark WM; and
[0085] .lambda..sub.0 is the wavelength .lambda.A, .lambda.B or
.lambda.C.
[0086] In this case, the angle .theta..sub.WM at which the light
fluxes L.sub.1(1) or L.sub.2(-1) enters is set so as to vary with
wavelength.
[0087] This construction allows the light flux LW generated from
the wafer mark WM to be reflected again by a beam splitter 28 after
passage through the projection optical system 3, the window
P.sub.0, the dichroic mirror 6, the objective lens 38 and the
parallel plane plate 37, followed by transmission through the lens
29 and the beam splitter 30 to a field diaphragm 31.
[0088] The field diaphragm 31 is disposed in the position in which
it conjugates with the wafer 4. Specifically, as indicated by the
oblique lines in FIG. 4(b), the field diaphragm 31 is provided with
an opening portion SWM in the position corresponding to the
position of the wafer mark WM of the wafer 4 in order to allow a
passage of only the diffraction light from the wafer mark WM of the
wafer 4.
[0089] The diffraction light from the wafer mark WM passed through
the field diaphragm 31 is subjected to filtering by a space filter
32 that can cut the zero-order diffraction light, thereby allowing
only the light flux LW to strike the dichroic mirror 44B and
thereafter the dichroic mirror 44A. The dichroic mirror 44B has the
characteristic of selecting wavelengths in such a manner that only
the light flux LCW having the wavelength .lambda.C in the light
flux LW from the wafer mark WM of the wafer 4 can be reflected and
the rest of the light fluxes LAW and LBW having the respective
wavelengths .lambda.A and .lambda.B are allowed to pass
therethrough. The light flux LCW reflected at the dichroic mirror
44B is collimated with the lens 48C, followed by introduction into
an optical fiber 45C which has its propagation efficiency optimized
to the wavelength .lambda.C. Then, the light flux LCW is
transmitted through the optical fiber 46C and reaches the
photomultiplier 50C acting as a photodetector, as shown in FIG. 1,
which can photoelectrically detect the optical beat signals having
a frequency (f.sub.1-f.sub.2) and containing information on the
position of the wafer 4. The signals generated from the
photomultiplier 50C are supplied through a low-path filter circuit
(not shown) capable of passing signals having a frequency of
approximately f.sub.1/2 to a phase detection comparison system 43
as wafer beat signals SWC.
[0090] On the other hand, as shown in FIG. 2, the light fluxes LAW
and LBW which in turn have passed through the dichroic mirror 44B
enter into the dichroic mirror 47A that has the characteristic for
selecting wavelengths such that the light flux LBW with the
wavelength .lambda.B can be reflected thereby and that the light
flux LAW with the wavelength .lambda.A is allowed to pass
therethrough. The light flux LBW reflected by the dichroic mirror
47A is collimated by the lens 45B and is then introduced into the
optical fiber 46B with its propagation efficiency optimized to the
wavelength .lambda.B, followed by transmission to a photomultiplier
50B, as shown in FIG. 1. The light flux LBW transmitted thereto is
then processed in the same manner as the light flux LCW as
described hereinabove to generate wafer beat signals SWB. On the
other hand, the light flux LAW passed through the dichroic mirror
44A is collimated by the lens 43A and introduced into the optical
fiber 46A with its propagation efficiency optimized to the
wavelength .lambda.A, followed by transmitting to a photomultiplier
50A of FIG. 1 and generating wafer beat signals SWA in
substantially the same manner as the light fluxes LBW and LCW.
[0091] The space filter 32 of FIG. 2 is disposed in a position
approximately conjugated with the pupil of the alignment optical
system, more specifically, conjugated substantially with the pupil
of the projection optical system 3 (the exit pupil), so as to block
a passage of the zero-order diffraction light (regularly reflected
light) from the wafer mark WM on the wafer 4 therethrough and to
allow a passage of only the light flux LW (the diffraction light
generating in the direction perpendicular to the diffraction
grating mark of the wafer 4) therethrough. In other words, the
light flux LW alone can passed through the space filter 32 yet the
zero-order diffraction light of the diffraction light generated
from the wafer mark WM cannot pass therethrough. Likewise, the
space filter 35 of FIG. 2 is disposed in a position approximately
conjugated with the pupil of the alignment optical system, more
specifically, conjugated substantially with the pupil of the
projection optical system 3 (the exit pupil), thereby capable of
blocking the zero-order diffraction light (regularly reflected
light) from the reticle mark RM on the reticle 1 and allowing a
passage of only the light flux LR (the diffraction light generating
in the direction perpendicular to the diffraction grating mark of
the reticle 1). In other words, the light flux LR alone can pass
through the space filter 35 yet the zero-order diffraction light of
the diffraction light generated from the reticle mark RM cannot
pass therethrough.
[0092] Each of the optical fibers 46A, 46B and 46C which are
employed as part of an alignment light recipient system, into which
the light fluxes LAW, LBW and LCW generated from the wafer mark WM
are introduced, has thier propagation efficiency optimized to each
of the respective wavelengths .lambda.A, .lambda.B and .lambda.C of
the corresponding light fluxes. Likewise, each of the optical
fibers 49A, 49B and 49C which are employed as part of an alignment
light recipient system, into which the light fluxes LAR, LBR and
LCR generated from the reticle mark RM are introduced, has thier
propagation efficiency optimized to each of the respective
wavelengths .lambda.A, .lambda.B and .lambda.C of the corresponding
light fluxes. For each optical fiber, however, the characteristic
for holding a plane of polarization may be optional.
[0093] With the arrangement of the alignment optical system as
described hereinabove, each of the three beat signals SRA, SRB and
SRC obtained through the low-path filter circuit (not shown) from
the respective photomultipliers 51A, 51B and 51B of the position
detection system for detecting the position of the reticle 1
contains optical beat signals of a sinusoidal wave form, each
having the same frequency .DELTA.f (=f.sub.1-f.sub.2). Further,
each of the three beat signals SWA, SWB and SWC obtained through
the low-path filter circuit (not shown) from the respective
photomultipliers 50A, 50B and 50B of the position detection system
for detecting the position of the wafer 4 contains optical beat
signals of a sinusoidal wave form, each having the same frequency
.DELTA.f (=f.sub.1-f.sub.2). Each of the six optical beat signals
of the sinusoidal wave form having the frequency .DELTA.f can be
extracted with high precision from the photoelectrical signals by
an optical beat signal extracting portion (Fourier transform
circuit) in the phase detection comparison system 43.
[0094] When the reticle 1 and the wafer 4 are allowed to locate in
optional positions in such a state that they are not aligned with
each other, each of the respective optical beat signals is deviated
by a constant phase. The phase difference (.+-.180.degree. or less)
between each of the optical beat signals from the reticle 1 and the
wafer 4 corresponds primarily to the amount of deviation of the
relative positions by a 1/2 pitch or less of the grating of the
diffraction grating mark formed on each of the reticle 1 and the
wafer 4.
[0095] Therefore, as the reticle 1 and the wafer 4 are moved
relative to each other in the direction of the orientation of the
grating, the amount of deviation of the relative positions between
the reticle 1 and the wafer 4 is pre-aligned with each other with
the precision of a 1/2 pitch or less of the grating of the reticle
mark RM and the wafer mark WM. The main control system 41 is
constructed in such a way that the reticle stage 2 or the wafer
stage 5 is moved in two-dimensional or x- and y-axial directions by
a survo system 42 so as to align the reticle 1 with the wafer 4 by
making the phase difference determined by the phase difference
detection system 43 zero or a predetermined value. This
construction can align the reticle 1 with the wafer 4 with a high
degree of precision.
[0096] Now, description will be made of the way in which the phase
difference detection system 43 detects and determines the phase
difference. The phase difference detection system 43 is so adjusted
as to detect a phase difference .DELTA..phi..sub.1 between the
wafer beat signal SWA and the reticle beat signal SRA, a phase
difference .DELTA..phi..sub.2 between the wafer beat signal SWB and
the reticle beat signal SRB, and a phase difference
.DELTA..phi..sub.3 between the wafer beat signal SWC and the
reticle beat signal SRC. The phase differences .DELTA..phi..sub.1,
.DELTA..phi..sub.2 and .DELTA..phi..sub.3 represent relative
movement distances .DELTA..phi..sub.1, .DELTA..phi..sub.2 and
.DELTA..phi..sub.3, respectively, between the wafer mark WM and the
reticle mark RM relative to the pitch P.sub.WM, according to the
following relationships:
.DELTA.x1=.DELTA..phi..sub.1.times.P.sub.WM/(4.pi.) (3)
.DELTA.x2=.DELTA..phi..sub.2.times.P.sub.WM/(4.pi.) (4)
.DELTA.x3=.DELTA..phi..sub.3.times.P.sub.WM/(4.pi.) (5)
[0097] When the measurement is implemented by the wavelengths
.lambda.A, .lambda.B and .lambda.C, it is ideal that the relative
movement distances .DELTA.x.sub.1, .DELTA.x.sub.2 and
.DELTA.x.sub.3, respectively, become equal to each other. As a
circuit pattern of a semiconductor or the like comprises a laminate
structure of thin films, however, it is not always the case that
the wafer mark WM sustains its symmetrical grating shape during
manufacture or in a particular layer. For example, a reference mark
FM provided on the wafer stage 5 of FIG. 5 is aligned in advance
and measurement is performed in the same manner as for detection of
the position of the wafer mark WM, and so-called baseline checking
is implemented to provide the phase differences
.DELTA..phi.0.sub.1, .DELTA..phi.0.sub.2 and .DELTA..phi.0.sub.3
between the reference mark FM and the reticle mark RM. Then, the
wafer mark WM is aligned within the precision of plus minus
.+-.P.sub.WM/4 or less by a search alignment sensor, although not
shown, and the phase differences .DELTA..phi.1, .DELTA..phi.2 and
.DELTA..phi.3 in this case are measured. By comparing the phase
differences in this case with those phase differences as measured
by the baseline checking method, the precise position of the wafer
mark WM is determined.
[0098] In that case, the ratios of the amplitudes of the wafer beat
signals SWA, SWB and SWC corresponding to the wafer mark WM (the
amplitudes of the beat signals in a sine wave form) to the
amplitudes of the wafer beat signals SWA, SWB and SWC at the time
of measuring the reference mark FM are determined as w1, w2 and w3,
respectively, and weigh-averaged the ratios, the phase difference
can be calculated from their weigh-averaged values in accordance
with the following formula: 1 = { w1 .times. ( 0 1 - 1 ) + w2
.times. ( 0 2 - 2 ) + w3 .times. ( 0 3 - 3 ) } / ( w1 + w2 + w3 ) (
6 )
[0099] It is also possible to utilize as a reference signal a drive
signal for driving the AOM 17 at the time of implementing the
baseline checking, in place of the signal for detecting the
position of the reference mark FM provided on the wafer stage
4.
[0100] In this embodiment, a detailed description will be made of
the specific construction and the principle of generating two light
fluxes having different frequencies with reference to FIG.
5(a).
[0101] As shown in FIG. 5(a), when a light flux LI as mixed light
consisting of the light fluxes LA, LB and LC strikes a first AOM
17A in the perpendicular direction thereto, the zero-order
diffraction light LA, plus first-order diffraction light
L.sub.0(1), minus first-order diffraction light L.sub.0(-1), and
other higher-order diffraction light are generated for each
wavelength from the AOM 17A by the Raman-Nath diffraction action of
the AOM 17A. The light fluxes are then entered into a second AOM
17B in the perpendicular direction thereto. In this case, when the
diffraction angle of the diffraction light in the direction of the
normal of the AOM 17A is set as 2.phi., the wavelength of the wave
55A within the AOM 17A is set as .LAMBDA..sub.G, the speed of the
wave 55A is set as v, the wavelength of the light flux LI is set as
.lambda. (frequency f.sub.0), and the order of the diffraction
light is set as the first order, the following relationship can be
established:
.LAMBDA..sub.G=v/f.sub.1 (7)
sin 2.phi.=.lambda./.LAMBDA..sub.G (8)
[0102] The zero-order diffraction light LA from the first AOM 17A
generates the zero-order diffraction light, plus first-order
diffraction light L.sub.A(1), minus first-order diffraction light
L.sub.A(-1), and other higher-order diffraction light for each
wavelength from an AOM 17B by the Raman-Nath diffraction action of
the AOM 17B. In this embodiment, there is employed a light flux
L.sub.1(1) obtained by mixing the light flux of the plus
first-order diffraction light L.sub.0(1) from the AOM 17A, which
has passed intact through the AOM 17B, with the plus first-order
diffraction light L.sub.A(1) from the AOM 17B. Further, there is
employed a light flux L.sub.2(-1) obtained by mixing the light flux
of the minus first-order diffraction light L.sub.0(-1) from the AOM
17A, which has passed intact through the AOM 17B, with the plus
first-order diffraction light L.sub.A(-1) from the AOM 17B. In
addition, the plus first-order diffraction light L.sub.0(1) from
the AOM 17A is subjected to frequency modulation to frequency
(f.sub.0+f.sub.1) and the plus first-order diffraction light
L.sub.A(1) from the AOM 17B is subjected to frequency modulation to
frequency (f.sub.0-f.sub.2). Likewise, the minus first-order
diffraction light L.sub.0(-1) from the AOM 17A is subjected to
frequency modulation to frequency (f.sub.0-f.sub.1) and the minus
first-order diffraction light L.sub.A(-1) from the AOM 17B is
subjected to frequency modulation to frequency (f.sub.0+f.sub.2).
Substantially, the modulated frequency of the light flux L.sub.1(1)
is (f.sub.1-f.sub.2)/2, and the modulated frequency of the light
flux L.sub.2(-1) is (f.sub.2-f.sub.1)/2.
[0103] In this embodiment, too, the distance s determined by
translation into the air length between the center P of the
supersonic action region 56A of the AOM 17A and the center Q of the
supersonic action region 56B of the AOM 17B is set so as to satisfy
the condition of the formula (9) or (10) as follows:
(m-1/3).LAMBDA..sup.2/.lambda.<s<(m+1/3).LAMBDA..sup.2/.lambda.
(9)
(m-1/3)v.sup.2/(.lambda.f.sub.2)<s<(m+1)v.sup.2/(.lambda.f.sub.2)
(10)
[0104] wherein m is an integer.
[0105] FIG. 5(b) shows the instance where the construction of FIG.
5(a) is decomposed into light fluxes having three colors, because
the light flux LI is a mixed light consisting of the light fluxes
LA, LB and LC. The light flux L.sub.1(1) in FIG. 5(a) can be
decomposed into the plus first-order diffraction lights LA(1),
LB(1) and LC(1) by modulating the frequencies of the light flux LA
with the wavelength .lambda.A, the light flux LB with the
wavelength .lambda.B and the light flux LC with the wavelength
.lambda.C, respectively, by (f.sub.1-f.sub.2)/2. Likewise, the
light flux L.sub.2(-1) can be decomposed into the minus first-order
diffraction lights LA(-1), LB(-1) and LC(-1) by modulating the
frequencies of the light flux LA with the wavelength .lambda.A, the
light flux LB with the wavelength .lambda.B and the light flux LC
with the wavelength .lambda.C, respectively, by
(f.sub.1-f.sub.2)/2. The other light fluxes are blocked by a space
filter 19.
[0106] FIG. 6 shows the manner in which the light fluxes L.sub.1(1)
and L.sub.2(-1) modulated by the AOMs 17A and 17B, respectively,
strike the wafer mark WM of a diffraction grating and the plus and
minus first-order diffraction light are generated in an upwardly
perpendicular direction. As shown in FIG. 6, there is generated
light flux LW consisting of a mixture of the minus first-order
diffraction light of each of the plus first-order diffraction light
LA(1), LB(1) and LC(1) with the plus first-order diffraction light
of each of the minus first-order diffraction light LA(-1), LB(-1)
and LC(-1). The light flux LW consists of light flux LAW comprised
of the plus minus first-order diffraction light having the
wavelength .lambda.A, the light flux LBW comprised of the plus
minus first-order diffraction light having the wavelength
.lambda.B, and the light flux LCW comprised of the plus minus
first-order diffraction light having the wavelength .lambda.C.
Likewise, each of the reticle mark RM and the reference mark FM
generates interference light having three different wavelengths in
substantially the same manner as described hereinabove.
[0107] This embodiment adopts an alignment sensor of a heterodyne
interference type in the LIA system using three different kinds of
colors and this enables alignment with an extremely high degree of
precision. As shown in FIG. 1, however, this type of apparatus
requires the disposition of six photomultipliers 50A-50C and
51A-51C, each inclusive, as photodetectors in the light recipient
system of the alignment device and light sources 10A-10C,
inclusive, consisting of three laser diodes as alignment light
sources. The photomultipliers and the light sources also act as
heat sources that cause a rise in the temperature and the
temperature gradient around the ambient environment. On the other
hand, exposure apparatuses for use in manufacturing semiconductors
or the like are provided with a number of optical units such as the
projection optical system 3 and so on. Therefore, they require
extremely stringent temperature management in order to prevent the
optical units from causing any aberration due to thermal expansion
and at the same time to prevent the wafer 4 as a substrate from
causing any adverse effect on the precision of superimposition of
on circuit patterns due to thermal expansion.
[0108] In accordance with the present invention, therefore,
improvements have been made with the purpose of eliminating or
reducing such an influence of heat generation to a great extent by
locating the photomultipliers 50A-50C and 51A-51C as potential heat
sources as well as the light sources 10A-10C, each inclusive,
separate from the exposing main body portion of the exposure
apparatus and transmitting the alignment detection light and the
alignment illumination light via the optical fibers 11A-11C,
46A-46C and 49A-49C, each inclusive.
[0109] Further, as each of the optical fibers 11A-11C, inclusive,
which function as a light transmission system and the optical
fibers 46A-46C and 49A-49C, each inclusive, which function as a
light recipient system, are arranged so as to transmit only the
light flux of the wavelength with its propagation efficiency
optimized, the light flux of each wavelength can be employed with
the highest possible efficiency. Furthermore, the present invention
can remove the risk that noise may arise upon transmission of a
light flux of multiple wavelengths through one optical fiber or
that an error in alignment may arise when the wavelengths have
different propagation efficiencies.
[0110] Second Embodiment
[0111] A second embodiment of the present invention will be
described with reference to FIG. 7, in which the present invention
is applied to an alignment sensor of a heterodyne interference type
in the projection exposure apparatus of the LIA system. Although
the plus minus first-order diffraction light generated by the
heterodyne interference is employed as a light for detection in the
first embodiment, there are also employed in the second embodiment,
as a light for detection, the zero-order light and the plus minus
second-order light, generated simultaneously in the reticle mark
RM, the wafer mark WM and the reference mark FM. As the optical
beat signals can also be generated by interference between the
zero-order light and the plus second-order light and between the
zero-order light and the minus second-order light, the optical beat
signals can be employed, too, for detecting the positions of the
marks in substantially the same manner as in the first embodiment.
As the wavelength selection means of the light recipient system,
there may be employed a dichroic mirror by applying the principle
in the same manner as employed in the first embodiment. Further, as
it is required for each wavelength to transmit interference light
consisting of the plus and minus first-order light, interference
light consisting of the zero-order light and the plus second-order
light, and interference light consisting of the zero-order light
and the minus second-order light, three optical fibers are required
for each wavelength as a light recipient system, for example, for
the wafer mark WM, so that a total of 9 of optical fibers are
required.
[0112] FIG. 7 illustrates the manner of generation of diffraction
light from the wafer mark WM by the light fluxes LA(1) and LA(-1)
of wavelength .lambda.A. As shown in FIG. 7, light flux
(interference light) LAW consisting of minus first-order
diffraction light LA(1).sup.-1 of the light flux LA(1) and plus
first-order diffraction light LA(-1).sup.+1 of the light flux
LA(-1) is arranged so as to generate upwardly in a perpendicular
direction. Further, light flux LEW obtained by the synthesis of
minus second-order diffraction light LA(1).sup.-2 of the light flux
LA(1) and regularly reflected light (zero-order light) LA(-1).sup.0
of the light flux LA(-1) is arranged so as to generate in the
direction in which the light flux LA(1) enters. Likewise, light
flux LDW obtained by the synthesis of zero-order light LA(1).sup.0
of the light flux LA(1) and second-order diffraction light
LA(-1).sup.+2 of the light flux LA(-1) is arranged so as to
generate in the direction in which the light flux LA(-1) enters.
The light fluxes LAW, LBW and LCW, each having the wavelength
.lambda.A, are then transmitted each to each of the discrete
photodetectors via respective optical fibers. For each of the
different wavelengths .lambda.B and .lambda.C, substantially the
same processes have been carried out as the light fluxes LA(1) and
LA(-1) of the wavelength .lambda.A.
[0113] Thereafter, alignment may be implemented using interference
light generated by interference, for example, between the
zero-order light and the plus or minus second-order diffraction
light, out of the three different types of light. In this case, the
wafer beat signal of the interference light generated by
interference between the zero-order light and the plus second-order
diffraction light of the light fluxes LA(1) and LA(-1) each having
the wavelength .lambda.A on the wafer mark WM is first given and a
phase difference of the wafer beat signal from the reticle beat
signal SRA is given as .DELTA..phi.(+2).sub.1. Further, the wafer
beat signal of interference light generated by interference between
the zero-order light and the minus second-order diffraction light
of the light fluxes LA(1) and LA(-1) each having the wavelength
.lambda.A on the wafer mark WM is given and a phase difference of
the wafer beat signal from the reticle beat signal SRA is given as
.DELTA..phi.(-2).sub.1. The phase differences
.DELTA..phi.(+2).sub.1 and .DELTA..phi.(-2).sub.1 are then averaged
to give an average phase difference .DELTA..phi.2.sub.1. Likewise,
the phase differences .DELTA..phi.(+2).sub.2 and
.DELTA..phi.(-2).sub.2 are given for the light fluxes LA(1) and
LA(-1) each having the wavelength .lambda.B and they are averaged
to give an average phase difference .DELTA..phi.2.sub.2. Further,
the phase differences .DELTA..phi.(+2).sub.3 and
.DELTA..phi.(-2).sub.3 are given for the light fluxes LA(1) and
LA(-1) having the wavelength .lambda.C and they are averaged to
give an average phase difference .DELTA..phi.2.sub.3. From these
average phase differences, the relative movement distances
.DELTA.x.sub.1, .DELTA.x.sub.2, and .DELTA.x.sub.3 of the wafer
mark WM can be given in substantially the same manner as in the
first embodiment in accordance with the following formulas:
.DELTA.x.sub.1=.DELTA..phi.2.sub.1.times.P.sub.WM/(4.pi.) (11)
.DELTA.x.sub.2=.DELTA..phi.2.sub.2.times.P.sub.WM/(4.pi.) (12)
.DELTA.x.sub.3=.DELTA..phi.2.sub.3.times.P.sub.WM/(4.pi.) (13)
[0114] It is to be noted herein that whichever result of alignment
performed using the phase differences .DELTA..phi..sub.1,
.DELTA..phi..sub.2 and .DELTA..phi..sub.3 given by the plus and
minus first-order diffraction light or the phase differences
.DELTA..phi.2.sub.1, .DELTA..phi.2.sub.2 and .DELTA..phi.2.sub.3
given by the zero-order light and the plus or minus first-order
diffraction light, can be selected as a final result, by weighing
by the amplitude (output) of the optical beat signals, by selecting
whichever the larger amplitude is, or by using whichever the
smaller an error of superimposition is by actually implementing the
alignment using the above phase differences in two ways and
measuring the error of superimposition of circuit patterns.
[0115] Third Embodiment
[0116] A third embodiment of the present invention will be
described hereinafter with reference to FIG. 8 which illustrates an
embodiment in which a light flux having three different wavelengths
is transmitted via one equal optical fiber and is divided into the
respective three wavelengths immediately before reaching
photodetector. In FIG. 8, the same elements as those illustrated in
FIGS. 1 and 2 are provided with the same reference numbers and
duplicate description of those elements will be omitted from the
following explanation.
[0117] FIG. 8 shows the essential portion of the light recipient
system of an alignment sensor to be employed in the third
embodiment of the present invention. As shown in FIG. 8, this
embodiment has the same construction as in the first embodiment
until the light flux LW having three different wavelengths from the
wafer mark WM of FIG. 2 passes through the space filter 32.
Thereafter, in this embodiment, the light path extending from the
space filter 32 is provided with a lens 45D that is so arranged as
to converge the light flux LW and then transmit it to an optical
fiber 46 capable of propagating the light flux having the three
different wavelengths .lambda.A, .lambda.B and .lambda.C, followed
by transmission through the optical fiber 46 immediately before a
dichroic mirror 44B. The light flux LW generated from the optical
fiber 46 is collimated by a lens 45E and allowed to enter into the
dichroic mirror 44B that reflects a light flux LCW having
wavelength .lambda.C. The light flux LCW reflected from the
dichroic mirror 44B is then transmitted to a photomultiplier 51C.
The dichroic mirror 44B allows the light fluxes having different
wavelengths to pass therethrough, and they are allowed to enter
into a dichroic mirror 44A. The dichroic mirror 44A reflects the
light flux LBW with wavelength .lambda.B that in turn strikes a
photomultiplier 51B and allows the light flux LAW with wavelength
.lambda.A to pass therethrough. The light flux LAW passed through
the dichroic mirror 44A is then allowed to enter into a dichroic
mirror 51A. The position of the wafer mark WM can be detected in
substantially the same manner as in the first embodiment according
to the present invention.
[0118] As the light flux LW is transmitted via the optical fiber 46
immediately before selection of the wavelengths by the dichroic
mirrors 44A and 44B, the third embodiment according to the present
invention offers the advantage that alignment can be made in a
stable manner because only one optical fiber is required which
creatly reduces disturbance of the light flux LW due to turbulence
of air existing around the ambient environment. It is to be noted,
however, that this embodiment as shown in FIG. 8 requires an
optical fiber 46 for each of the three different wavelengths
.lambda.A, .lambda.B and .lambda.C, each having substantially the
same propagation characteristics. Therefore, if such optical fibers
are not available, the first embodiment is preferred.
[0119] In the first, second and three embodiments according to the
present invention, each embodiment adopts an alignment sensor of
the heterodyne interference type in the LIA system. In each of the
embodiments, however, it is also possible to use an alignment
sensor of a homodyne interference type or in an LSA system.
[0120] In this embodiment, too, it is possible to locate the light
sources 10A-10C. and the photomultipliers 50A-50C and 51A-51C, each
inclusive, in a chamber different and separate from a chamber with
the main body portion 8 of the exposure apparatus with the
alignment optical system 9 of FIG. 1 disposed therein. This
construction makes management of the exposure apparatus easier than
a construction in which they are provided together in one chamber.
Further, it is expected that this construction will greatly improve
alignment precision. As a photodetector, there may be employed a
photodiode or the like, in place of the photomultipliers 50A-50C
and 51A-51C.
[0121] In accordance with the present invention, this embodiment in
particular can offer the features and advantages that a detecting
substrate to be detected can be separated or isolated from a
photodetector acting as a heat source by locating an optical guide
leading the light flux coming from the mark for position detection
to the photodetector and that any reduction in precision of the
position detection due to thermal expansion, etc. of the detecting
substrate can be prevented, thereby allowing position detection
with a high level of precision. In this case, further, as the light
flux coming from the mark for position detection is led through the
optical guide, this embodiment can enables the influence of
turbulence of ambient air during transmission and the like to be
prevented.
[0122] In accordance with the present invention, it is further
noted that, as the light flux to be employed for position detection
comprises a light flux having multiple wavelengths, the light flux
of each wavelength can be utilized effectively when the light flux
coming from the mark for position detection is led to a
photodetector via a different optical guide for each of the
multiple wavelengths. This arrangement provides the merit that the
influence of heat generated can be reduced even if a photodetector
is employed for each of the different wavelengths.
[0123] Further, the present invention offers the features and
advantages that position detection for each of the wavelengths can
be conducted with a high degree of precision and as a result,
position detection precision can be improved to a remarkable extent
due to the fact that the light flux to be employed for the position
detection for each wavelength is not attenuated during transmission
through a plurality of optical guides, when each of the optical
guides is an optical fiber with its propagation efficiency
optimized so as to allow only the light flux as an object of
propagation to reflect and the rest to pass therethrough.
[0124] The present invention further provides merits that position
detection can be performed in the LIA system that transmits
multiple interference light of position detection of each of the
order of diffraction via an optical fiber and that it detects each
of the light fluxes photoelectrically. In accordance with the
present invention, such merits can be achieved particularly by the
construction of the mark for position detection and the
photodetectors. In other words, there is employed, as a mark for
position detection, a mark of a diffraction grating form having
predetermined pitches arranged of measurement, and the illumination
optical system is so arranged as to illuminate a multiplicity of
mutually coherent light fluxes as the light flux for position
detection from different directions on the mark of the diffraction
grating form. More specifically, first interference light
consisting of multiple diffraction light generated from the
diffraction grating mark in a direction parallel to a first
direction is received by a first photodetector, second interference
light consisting of multiple diffraction light generated from the
diffraction grating mark in a direction parallel to a second
direction yet different from the first direction is received by a
second photodetector, and two optical guides are disposed so as to
lead the first and second interference light to the respective
photodetectors that are disposed separately and independently from
each other.
[0125] The additional feature and advantage achieved by the present
invention resides in the fact that the light source acting as a
heat source can be separated and isolated from the illumination
optical system and therefore thermal expansion of the substrate,
etc. to be detected can be minimized to thereby improve in
alignment precision to a great extent by utilizing a light flux
having multiple wavelengths as the light flux for position
detection and by leading the light flux with the multiple
wavelengths to the illumination optical system via an optical guide
for each of the different wavelengths.
[0126] With the arrangement of the exposure apparatus according to
the present invention, a high degree of precision in alignment can
be achieved because the generation of heat from the position
detection system is adjusted so as to anoid adversely affecting the
main body portion of the exposure apparatus, photosensitizable
substrate and other elements.
[0127] Fourth Embodiment
[0128] Description will now be made of a fourth embodiment of an
exposure apparatus according to the present invention, with
reference to FIG. 9. This embodiment is an embodiment in which the
present invention is applied to a projection exposure apparatus of
a stepper type having an alignment system of the LIA method wherein
a light flux of multiple wavelengths is employed.
[0129] FIG. 9 illustrates the projection exposure apparatus
according to the fourth embodiment of the present invention. In
FIG. 9, at the time of exposure, illumination light IL for exposure
generated from an exposing light source system 100 consisting of a
light source such as, for example, a superhigh pressure mercury
lamp or excimer laser, a shape adjusting lens, an optical
integrator and so on is so arranged as to illuminate a pattern area
of a reticle R at a nearly uniform distribution of illuminance
through an illumination optical system 101 containing a reticle
blind, a main condenser lens and so on. The illumination light IL
passed through the pattern area of the reticle R then strikes a
projection optical system PL with both telecentric sides or one
telecentric side, which in turn compresses the pattern image of the
reticle R, for example, to 1/5 of the original size of the pattern
thereof, and the compressed pattern image is then projected and
exposed to one shot area on a wafer W the surface of which is
coated with a photoresist layer and which is held in such a way
that its surface is substantially aligned with the plane of the
projection optical system PL on which the best possible image is
formed.
[0130] Now, specific description will be made of the construction
of the exposure apparatus with reference to FIG. 9, in which the
direction parallel to the optical axis AX of the projection optical
system PL is set as a z-axis, the direction parallel to the paper
surface of FIG. 9 on the plane perpendicular to the z-axis is set
as an x-axis, and the direction perpendicular to the paper surface
of FIG. 9 is set as a y-axis.
[0131] The wafer W is held on a wafer stage 102 through a wafer
holder, although not shown, and the wafer stage 102 is disposed in
such a way that the wafer W can be aligned in the x- and
y-directions by a step-and-repeat system and that it is moved in
the z-direction by an autofocus system. The x- and y-directional
coordinates of the wafer stage 102 is always monitored by a laser
interferometer 103, and the measurement results are supplied to a
main control system 104 for managing and controlling the entire
action of the apparatus, thereby controlling the action of the
wafer stage 102 via a stage drive system 105 on the basis of the
coordinates supplied to the main control system 104.
[0132] The main body portion (the exposing main body portion) of
the projection exposure apparatus having the above construction is
located in a chamber 106 that is controlled so as to maintain
moisture and temperature conditions constant so as to stabilize
precision in dimension at the time of alignment and at the time of
exposure to light.
[0133] Next, description will be made of the alignment system of
the exposure apparatus according to this embodiment of the present
invention. The alignment system employed in this embodiment
comprises an alignment system in the LIA system and in a heterodyne
system, in which the light flux with multiple wavelengths is
employed. In this embodiment, the detecting principle of the
alignment system in both the x- and y-directions is substantially
the same and consequently the detecting principle of the alignment
system in the y-direction alone will be described. Each of the shot
areas of the wafer W is further provided with a wafer mark of a
diffraction grating form for each of the x-axis and the y-axis. In
this embodiment, as shown in FIG. 10, a y-axial wafer mark 3Y is
set as an object of detection, and it is a mark of a diffraction
grating form with projected portions formed by predetermined
pitches along the y-axial direction.
[0134] As shown in FIG. 9, two laser light sources 107 and 108,
each supplying light fluxes for alignment, have different
generation wavelengths .lambda.1 and .lambda.2, respectively, and
they are located in a chamber 109 different from a chamber 106 with
the exposing main body portion of the exposure apparatus located
therein. The chambers 106 and 109 are arranged so as to have their
interiors air-conditioned separately and independently from each
other. In FIG. 9, the laser beams LB1 having the wavelength
.lambda.1 coming from the laser light source 107 are transmitted
through a connection optical system 110 to a top end 112a of an
optical fiber 112 of a single mode. Likewise, the laser beams LB2
having the wavelength .lambda.2 coming from the laser light source
108 are transmitted through a connection optical system 111 to a
top end 113a of an optical fiber 113 of a single mode. As each of
the optical fibers 112 and 13, there may be employed one with its
propagation efficiency optimized for the wavelengths .lambda.1 and
.lambda.2 of the laser beams LB1 and LB2, respectively, and having
a low rate of attenuation. Both of the top ends 112a and 113a of
the respective optical fibers 112 and 113 are located in the
chamber 109, and both of the other top ends 112b and 113b of the
respective optical fibers 112 and 113 are located in the chamber
106. This disposition of the optical fibers enables the laser beams
LB1 and LB2 to be transmitted from the interior of the chamber 109
through the respective optical fibers 112 and 113 to the interior
of the chamber 106 without direct exposure to air within a clean
room during transmission.
[0135] In the chamber 106, the laser beams LB1 transmitted via the
optical fiber 112 and coming from the other top end 112b of the
optical fiber 112 and the laser beams LB1 transmitted via the
optical fiber 113 and coming from the other top end 113b of the
optical fiber 113, respectively, are then converted to parallel
light by lenses 114 and 115 and transmitted to dichroic mirrors 116
as a light flux synthesizer. The laser beams LB1 and LB2 are
synthesized by the dichroic mirror 116 to one laser beam LB.sub.3
that in turn strikes an audio optical element (hereinafter referred
to as "AOM") 117 as a heterodyne beam creation system. It is to be
noted herein that, in the current situation, as the AOM is
extremely high in drive frequency, laser beams (heterodyne beams)
having a predetermined difference of frequencies are created by
driving, for example, two AOMs by a high-frequency signal having
the predetermined difference of frequencies. As this technique is
known in the art, the description that follows will be directed to
the instance where the heterodyne beams are created using one AOM
117 for brevity of explanation. More specifically, the AOM 117 is
driven by drive signals having a frequency fd and has the function
of varying the frequency of the diffraction light of each order to
be diffracted within its inside by the value of the frequency fd.
The laser beams LB.sub.3 coming from the dichroic mirror 116 are
converted through the AOM 117 by the dichroic mirror 116 into
multiple diffraction beams having each of the wavelengths .lambda.1
and .lambda.2. The following description will be made of only the
plus and minus first-order diffraction light for brevity of
explanation.
[0136] The plus first-order diffraction light D.sup.+1 and the
minus first-order diffraction light D.sup.-1, each generated by
diffraction of the laser beam LB.sub.3 with the AOM 117, are
subjected to frequency modulation by +fd and -fd, respectively,
with respect to the zero-order diffraction light. The plus
first-order diffraction light D.sup.+1 and the minus first-order
diffraction light D.sup.-1 are transmitted to a beam splitter 118
and then to a lens 119 that makes their light fluxes parallel to
each other, followed by transmission of the parallel light fluxes
to a mirror 120 interposed between the projection optical system PL
and the reticle R. The mirror 120 turns the parallel light fluxes
so as to strike the projection optical system PL, and the light
fluxes are then focused on the wafer mark 3Y of the grating form
formed on the wafer W after the passage through the projection
optical system PL.
[0137] FIG. 10 illustrates the manner in which the plus first-order
diffraction light D.sup.+1 and the minus first-order diffraction
light D.sup.-1 of the laser beams LB.sub.3 strike the wafer mark
3Y. As shown in FIG. 10, the plus first-order diffraction light
D.sup.+1 consists of diffraction light D1.sup.+1 with wavelength
.lambda.1 and diffraction light D2.sup.+1 with wavelength
.lambda.2, and likewise the minus first-order diffraction light
D.sup.-1 consists of diffraction light D1.sup.-1 with wavelength
.lambda.1 and diffraction light D2.sup.-1 with wavelength
.lambda.2. The pitch of the wafer mark 3Y is selected so as to
generate interference light DS consisting of the plus and minus
first-order diffraction light to be generated from the wafer mark
3Y by irradiation of the plus first-order diffraction light
D.sup.+1 and the minus first-order diffraction light D.sup.-1 of
the laser beams LB.sub.3. Therefore, the wafer mark 3Y generates
interference light DS1 and DS2 upwardly in a perpendicular
direction, the interference light DS1 consisting of plus
first-order diffraction light DS1.sup.+1 and minus first-order
diffraction light DS1.sup.-1 of each of the diffraction light
D1.sup.+1 and D1.sup.-1, each having the wavelength .lambda.1, and
the interference light DS2 consisting of plus first-order
diffraction light DS2.sup.+1 and minus first-order diffraction
light DS2-1 of each of the diffraction light D2.sup.+1 and D2-1,
each having the wavelength .lambda.2. A synthesized light flux of
the diffraction light DS1 and DS2 is referred to as interference
light DS having two wavelengths. For each of the laser beams of the
wavelengths .lambda.1 and .lambda.2, the plus first-order
diffraction light D.sup.+1 and the minus first-order diffraction
light D.sup.-1 have a frequency difference of 2fd, so that the
interference light DS of the two wavelengths generated from the
wafer mark 3Y by irradiation of the plus first-order diffraction
light D.sup.+1 and the minus first-order diffraction light D.sup.-1
contains an optical beat component having the frequency 2fd.
Therefore, the optical beat component functions as an optical
signal for heterodyne detection.
[0138] Turning back to FIG. 9, the interference light DS reflected
from the wafer mark 3Y returns from the projection optical system
PL through the mirror 120 and the lens 119 back to the beam
splitter 118 in the opposite direction along the optical path
through which the laser beams LB3 have been transmitted to the
wafer mark 3Y, followed by turning the course of the interference
light DS by the beam splitter 118 to a photodetector 121 consisting
of a photodiode and so on. The interference light DS having two
wavelengths are photoelectrically converted into wafer beat signals
SW having frequency 2fd and the wafer beat signals SW are then
transmitted to an alignment processing system 122. The alignment
processing system 122 is so arranged as to create a reference beat
signal having frequency 2fd using the drive signals for the AOM 117
and to determine a phase difference between the reference beat
signal and the wafer beat signal SW. Based on the phase difference
between the reference beat signal and the wafer beat signal SW is
given an amount of deviation of the position of the wafer mark 3Y
in the y-axial direction, and this amount is supplied to the main
control system 104. In the main control system 104, the
y-coordinate of the wafer stage 102 is set as the y-coordinate of
the wafer mark 3Y, when the wafer stage 102 is driven so as to
make, for example, the amount of deviation of the position (the
phase difference) zero. Likewise, the x-axial coordinate of the
wafer mark is detected in the same manner as described hereinabove.
Thereafter, the alignment of the shot area and the exposure of the
pattern image of the reticle R to light are conducted on the basis
of the coordinates detected.
[0139] In this embodiment, two laser light sources 107 and 108 of
the alignment optical system acting as a heat source are located in
the chamber 109 different from the chamber 106 in which the main
body portion of the exposure apparatus is disposed. The separate
disposition of the chambers 106 and 109 does not result in any
adverse influence upon the main body portion of the exposure
apparatus or the wafer W as the substrate to be exposed to light
due to thermal expansion or for other reasons. Further, as the
laser beams LB1 and LB2 are transmitted from the chamber 109 to the
chamber 106 via the optical fibers 112 and 113, respectively, the
laser beams LB1 and LB2 are not exposed to the open air within both
of the chambers 109 and 106 so that the disturbance on the wave
planes of the laser beams LB1 and LB2 can be prevented from
occurring due to a vibration of the open air within the chambers
106 and 109, i.e. the air within the clean air. Therefore,
alignment can always be conducted with high precision.
[0140] In this embodiment, too, the laser beams LB1 of the
wavelength .lambda.1 generated in the chamber 109 are transmitted
via the optical fiber 112 of the single mode with its transmission
efficiency optimized for the wavelength corresponding to the laser
beams LB1. Likewise, the laser beams LB2 of the wavelength
.lambda.2 generated therein are transmitted via the optical fiber
113 of the single mode with its transmission efficiency optimized
for the wavelength corresponding to the laser beams LB2. The laser
beams LB1 and LB2 are then synthesized with the dichroic mirror 116
in the vicinity of the main body portion of the exposure apparatus
within the chamber 106, thereby enabling position detection using
the laser beams of each wavelength at a high SN ratio. Further, as
light having multiple wavelengths is transmitted by the same
optical fiber, noise which otherwise may arise due to disturbance
of the optical fiber induced by vibration or for other reasons at
the time of transmission can be suppressed averaging noise of each
of the wavelengths, thereby enabling improvements in alignment
precision.
[0141] Fifth Embodiment
[0142] Description will now be made of a fifth embodiment of the
exposure apparatus according to the present invention, with
reference to FIG. 11. In the fifth embodiment, a smaller chamber is
additionally located within a chamber in which the main body
portion of the exposure apparatus is disposed, and a light source
for laser beams with multiple wavelengths for alignment is disposed
in the smaller chamber. As shown in FIG. 11, the elements
corresponding to FIG. 9 are provided with the same reference
numerals as in FIG. 9 and detailed description thereof will be
omitted. In this embodiment, the construction of the main body
portion of the exposure apparatus and the alignment system and the
method for the position detection may be carried out in
substantially the same manner as for the exposure apparatus
according to the second embodiment of the present invention.
[0143] In FIG. 11, a chamber 106A is arranged to modify the chamber
106 of FIG. 9 so as to accommodate the chamber 109, and the chamber
106A is accommodated with the main body portion of the exposure
apparatus in substantially the same manner as shown in FIG. 9.
Further, a smaller chamber 123 is disposed in the chamber 106A and
it has substantially the same structure as the chamber 109 of FIG.
9. In this construction of the chambers, the laser beams LB1 and
LB2, each having two wavelengths, generated within the chamber 123,
are transmitted each to the alignment optical system outside of the
chamber 123 through the optical fibers 112 and 113,
respectively.
[0144] As shown in FIG. 11, the exposure apparatus in the fifth
embodiment of the present invention differs from the exposure
apparatus of the second embodiment in that the chamber 123 is
disposed within the inside of the chamber 106A and that the optical
fibers 112 and 113 are disposed so as not to be exposed directly to
air in the outside clean room. Further, as an air conditioning
machine 124 is disposed outside the chamber 106A, and it is
connected to the chamber 123 through air vent pipes 124a and 124b.
The inside of the chamber l23 is allowed to cool by the air
conditioning machine 124 to discharge the heat generated from the
laser light sources 107 and 108 to the outside of the chambers 106A
and 123 and at the same to prevent the heat from coming back into
the chamber 106A through a partition wall of the chamber 123. This
construction can serve as implementing alignment with a high degree
of precision.
[0145] In this embodiment, as the chamber 123 is of an sufficiently
adiabatic structure and the chamber 123 is allowed to cool by air
conditioning, the heat transmission into the chamber 106A can be
disregarded. Further, as the air conditioning machine 124 is
located outside the chamber 106A and the air is discharged and
introduced via a duct etc. having a high degree of heat insulation,
an influence of the heat generated by the air conditioning machine
124 can also be disregarded.
[0146] Furthermore, in this embodiment, as the optical fibers 112
and 113 are disposed so as not to be exposed directly to the open
air, i.e. to the air within the clean room, noises can be reduced
to a smaller extent due to vibration etc. of the optical fibers
resulting from disturbance of the air.
[0147] Sixth Embodiment
[0148] Description will now be made of the exposure apparatus
according to the fourth embodiment with reference to FIGS. 12 and
13. In this embodiment, the present invention is applied to a
projection exposure apparatus with an alignment system of the LSA
method. In FIG. 12, the portion corresponding to FIG. 9 is provided
.lambda.with the same reference numerals and description of the
details of the exposure apparatus is omitted.
[0149] In FIG. 12, only the alignment system in the y-axial
direction is indicated because the principle of alignment in the
x-axial and y-axial directions is the same.
[0150] As shown in FIG. 12, the laser beams LB1 with the wavelength
.lambda.1 and the laser beams LB2 with the wavelength .lambda.2 are
emitted from the laser light sources 107 and 108 disposed in the
chamber 109, respectively, in substantially the same manner as in
the embodiment of FIG. 9. The laser beams LB1 and LB2 are then
transmitted into the chamber 106 from the chamber 109 via the
optical fibers 112 and 113, respectively. The laser beams LB1 and
LB2 introduced into the chamber 106 from the chamber 109 via the
respective optical fibers 112 and 113 are converted with the lenses
114 and 115 into parallel light fluxes that in turn strike the
dichroic mirror 116 to synthesize them into one laser beam LB3. The
resulting laser beam LB3 are transmitted through the beam splitter
118 to the projection optical system PL via the mirror 120
interposed between the projection optical system PL and the reticle
R and is illuminated from the projection optical system PL on the
wafer mark on the wafer W.
[0151] FIG. 13 illustrates a wafer mark 3XA for the LSA system,
disposed in one shot area SA on the wafer W, consisting of dots
arranged linearly in the x-axis, a wafer mark 3YA for the y-axis
consisting of dots arranged linearly by predetermined pitches, and
the laser beams LB3 converged in a slit form in the x-direction,
acting as an alignment light flux for the y-axis. In FIG. 13, the
wafer mark 3YA consists of a row of dots (in the form of a linear
arrangement of dots) arranged by predetermined pitches, while the
wafer mark 3Y employed for the exposure apparatuses in the second
and third embodiments of the present invention is of the
diffraction grating form arranged by predetermined pitches. When
the wafer stage 102 of FIG. 12 is scanned in the y-direction and
the wafer mark 3YA reaches the position crossing the area for
converging the laser beams LB3, the wafer mark 3YA generates
diffraction light of multiple orders.
[0152] Referring back to FIG. 12, description will be made simply
of zero-order diffraction light and plus first-order diffraction
light from the wafer mark 3YA alone, each of the diffraction light
being from the laser beams LB1 and LB2, each having the wavelengths
.lambda.1 and .lambda.2, acting as components of the laser beams
B3, for brevity of explanation. In this example, the zero-order
diffraction light and the plus first-order diffraction light of the
laser beams LB1 with the wavelength .lambda.1 are set as DY.sup.10
and DY.sup.11, respectively, and the zero-order diffraction light
and the plus first-order diffraction light of the laser beams LB2
with the wavelength .lambda.2 are set as DY.sup.20 and DY.sup.21,
respectively. The diffraction light of each order is led to a beam
splitter 118 through the projection optical system PL and a mirror
120, and it is directed by the beam splitter 118 to a photodetector
121 along an optical path that deviates from the optical path of
the laser beams LB.sub.3. A space filter 125 is disposed on the
optical path of the zero-order diffraction light DY.sup.10 and
DY.sup.20 between the beam splitter 125 and the photodetector 121
so as to block a passage of the zero-order diffraction light
DY.sup.10 and DY.sup.20 that generate by reflection on the plane of
the wafer W regardless of coincidence of the wafer mark 3YA with
the laser beams LB.sub.3.
[0153] The photodetector 121 is so disposed as to detect only the
plus first-order diffraction light DY.sup.11 and DY.sup.21 that are
the light fluxes generating at the time when the wafer mark 3YA
coincides with the laser beams LB.sub.3, and the position of the
wafer mark 3YA is detected on the basis of an intensity of the plus
first-order diffraction light DY.sup.11 and DY.sup.21 detected by
the photodetector 121.
[0154] More specifically, a detecting signal SWA which is a signal
converted photoelectrically from the photodetector 121 is supplied
to an alignment processing system 122A. A main control system 104A
for managing and controlling the action of the entire apparatus in
this embodiment supplies a measured value of a laser interferometer
103 to the alignment processing system 122A upon movement of the
wafer stage 102 in the y-direction via a stage drive system 105 on
the basis of the coordinates of the wafer stage 102 by the laser
interferometer 103. Then, the alignment processing system 122A
holds, for example, the y-coordinate of the wafer stage 102 at the
time when the value of the detecting signal SWA takes a peak, as a
y-coordinate of the wafer mark 3YA, and it supplies the held
coordinate to the main control system 104A. The x-coordinate of the
x-axial wafer mark of the LSA system is detected in substantially
the same manner as described hereinabove.
[0155] In this embodiment, as the laser light sources 107 and 108
acting as the heat sources are disposed in the chamber 109 located
discretely from the chamber 106 with the main body portion of the
exposure apparatus disposed therein, no influence of the heat
generated by the heat sources is exerted upon the main body portion
thereof, thereby enabling the implementation of the position
detection with high precision. Further, in this embodiment, as the
laser beams LB1 and LB2, each of multiple wavelengths, are employed
as alignment light although the LSA system is adopted, a detecting
signal having a different wavelength can be effectively employed
even if a detecting signal having another wavelength would become
too small due to an influence that may be exerted by interference
on a thin layer by a photoresist coating or by a shape of the wafer
mark or for other reasons. This can also serve to conduct alignment
constantly with high precision. In addition, as the laser beams LB1
and LB2 are transmitted via the respective optical fibers 112 and
113 for different wavelengths, this embodiment provides the
advantage that the laser beams of each wavelength can be utilized
with maximal efficiency.
[0156] It is to be noted herein that, in the three embodiments as
described hereinabove, each uses the alignment system of a TTL
method. It is to be understood, however, that the present invention
can be apparently applied to an alignment system of a TTR
(through-the-reticle) method or of an off-axis method.
[0157] Further, in the embodiments as described hereinabove, it is
also possible to use light having three wavelengths or more as an
alignment light, in addition to light having two wavelengths
employed in the embodiments as described hereinabove.
[0158] It should be understood, however, that the present invention
is not limited in any respect to the embodiments as described
hereinabove and that the present invention can encompass any
variations and modifications without departing from the spirit and
scope of the present invention.
[0159] As described hereinabove, the exposure apparatus of the
present invention is provided with the position detection system
for aligning the mask pattern with the photosensitizable substrate,
which comprises a laser light source for generating laser light
with multiple wavelengths, an illumination optical system for
illuminating the laser light from the laser source onto a mark for
position alignment on the photosensitizable substrate, and a light
recipient optical system for receiving the laser light from the
mark for position alignment and in which the laser light sources
are located apart from the main body portion of the exposure
apparatus in an isolated way. Therefore, the present invention
offers the features and advantages that any adverse influence upon
the main body portion of the exposure apparatus and the
photosensitizable substrate by the heat generated by the laser
light sources having multiple wavelengths as sources for generating
heat can be excluded and the position detection can be implemented
with high precision using a light flux with multiple
wavelengths.
[0160] In accordance with the present invention, as the laser light
of multiple wavelengths is led from the laser light source to the
illumination optical system via different optical guides for
different wavelengths, the efficiency of transmission of the laser
light of each wavelength can be enhanced. Further, as noise can be
removed readily by averaging all of the wavelengths even if such
noise would be caused to occur by disturbance of the optical guides
due to vibration or for other reasons, thereby enabling position
detection to be effected with high precision.
[0161] In accordance with the present invention, as the light
recipient optical system is so arranged as to receive the
diffraction light generated by the laser light from the mark for
position alignment in the predetermined direction, the position
detection can effectively be implemented, for example, by the LIA
system.
[0162] Furthermore, in accordance with the present invention, the
illumination optical system is so arranged as to illuminate the
laser light of multiple wavelengths onto a mark for position
detection with dots arranged in a linear sequence and to detect the
position of the dots-line-shaped mark on the basis of a light
amount of the diffraction light received by the light recipient
optical system, so that the position detection can be implemented
by the LSA system using multiple wavelengths. Therefore, an
influence upon a thin layer on the photosensitizable substrate can
be reduced even by the LSA system.
* * * * *