U.S. patent application number 13/534933 was filed with the patent office on 2012-11-22 for movable body drive method and movable body drive system, pattern formation method and apparatus, exposure method and apparatus, and device manufacturing method for continuous position measurement of moveable body before and after switching between sensor heads.
This patent application is currently assigned to NIKON CORPORATION. Invention is credited to Yuho KANAYA, Yuichi SHIBAZAKI.
Application Number | 20120293788 13/534933 |
Document ID | / |
Family ID | 40032893 |
Filed Date | 2012-11-22 |
United States Patent
Application |
20120293788 |
Kind Code |
A1 |
SHIBAZAKI; Yuichi ; et
al. |
November 22, 2012 |
MOVABLE BODY DRIVE METHOD AND MOVABLE BODY DRIVE SYSTEM, PATTERN
FORMATION METHOD AND APPARATUS, EXPOSURE METHOD AND APPARATUS, AND
DEVICE MANUFACTURING METHOD FOR CONTINUOUS POSITION MEASUREMENT OF
MOVEABLE BODY BEFORE AND AFTER SWITCHING BETWEEN SENSOR HEADS
Abstract
A controller uses two Z heads, which are positioned above a
reflection surface installed on the .+-.X ends of the upper surface
of a table, to measure the height and tilt of the table. According
to the XY position of the table, the Z heads to be used are
switched from ZsR and ZsL to ZsR' and ZsL. On the switching of the
heads, the controller applies a coordinate linkage method to set an
initial value of the Z heads which are to be newly used.
Accordingly, although the Z heads to be used are sequentially
switched according to the XY position of the table, measurement
results of the height and the tilt of the table are stored before
and after the switching, and it becomes possible to drive the table
with high precision.
Inventors: |
SHIBAZAKI; Yuichi;
(Kumagaya-shi, JP) ; KANAYA; Yuho; (Kumagaya-shi,
JP) |
Assignee: |
NIKON CORPORATION
Tokyo
JP
|
Family ID: |
40032893 |
Appl. No.: |
13/534933 |
Filed: |
June 27, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12196133 |
Aug 21, 2008 |
8237919 |
|
|
13534933 |
|
|
|
|
60935669 |
Aug 24, 2007 |
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Current U.S.
Class: |
355/77 |
Current CPC
Class: |
G03F 7/70775 20130101;
G03F 7/7085 20130101; G03F 9/7026 20130101; G03F 9/7034
20130101 |
Class at
Publication: |
355/77 |
International
Class: |
G03B 27/32 20060101
G03B027/32 |
Claims
1. A movable body drive method in which a movable body is driven
substantially along a two-dimensional plane, the method comprising:
detecting a position of the movable body in a direction
perpendicular to the two-dimensional plane with a first sensor of a
plurality of sensors placed within an operating area of the movable
body, and controlling at least one of the position in the
perpendicular direction and a tilt with respect to the
two-dimensional plane of the movable body, and also obtaining
correction information to correct the detection results by a second
sensor different from the first sensor of the plurality of sensors,
using tilt information of the movable body with respect to the
two-dimensional plane obtained from detection results by the first
sensor, when starting a control using detection results by the
second sensor according to a movement in the two-dimensional plane
of the movable body.
2. A movable body drive method to drive a movable body at least in
a two-dimensional plane, wherein positional information of the
movable body in a direction perpendicular to the two-dimensional
plane is detected by at least one of a plurality of sensors having
detection points at different positions within the two-dimensional
plane, and on detecting positional information of the movable body
with a sensor different from the one sensor, detection information
of the one sensor and tilt information of the movable body with
respect to the two-dimensional plane are used, according to a
movement of the movable body.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is, a Division of application Ser. No. 12/196,133 filed
Aug. 21, 2008, which is a non-provisional application claims the
benefit of Provisional Application No. 60/935,669 filed Aug. 24,
2007. The prior applications, including the specifications,
drawings and abstract are incorporated herein by reference in their
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to movable body drive methods
and movable body drive systems, pattern formation methods and
apparatuses, exposure methods and apparatuses, and device
manufacturing methods, and more particularly, to a movable body
drive method and a movable body drive system that drives a movable
body along a substantially two-dimensional plane, a pattern
formation method using the movable body drive method and a pattern
formation apparatus equipped with the movable body drive system, an
exposure method using the movable body drive method, and an
exposure apparatus equipped with the movable body drive system, and
a device manufacturing method using the pattern formation
method.
[0004] 2. Description of the Background Art
[0005] Conventionally, in a lithography process for manufacturing
electron devices (microdevices) such as semiconductor devices (such
as integrated circuits) and liquid crystal display devices,
exposure apparatuses such as a projection exposure apparatus by a
step-and-repeat method (a so-called stepper) and a projection
exposure apparatus by a step-and-scan method (a so-called scanning
stepper (which is also called a scanner) are mainly used.
[0006] However, the surface of a wafer serving as a substrate
subject to exposure is not always flat, for example, by undulation
and the like of the wafer. Therefore, especially in a scanning
exposure apparatus such as a scanner and the like, when a reticle
pattern is transferred onto a shot area on a wafer by a scanning
exposure method, positional information (surface position
information) related to an optical axis direction of a projection
optical system of the wafer surface is detected at a plurality of
detection points set in an exposure area, for example, using a
multiple point focal point position detection system (hereinafter
also referred to as a "multipoint AF system") and the like, and
based on the detection results, a so-called focus leveling control
is performed (refer to, for example, Kokai (Japanese Patent
Unexamined Application Publication) No. 6-283403) to control the
position in the optical axis direction and the inclination of a
table or a stage holding a wafer so that the wafer surface
constantly coincides with an image plane of the projection optical
system in the exposure area (the wafer surface is within the focal
depth of the image plane).
[0007] Further, with the stepper or the scanner and the like,
wavelength of exposure light used with finer integrated circuits is
becoming shorter year by year, and numerical aperture of the
projection optical system is also gradually increasing (larger NA),
which improves the resolution. Meanwhile, due to shorter wavelength
of the exposure light and larger NA in the projection optical
system, the depth of focus had become extremely small, which caused
a risk of focus margin shortage during the exposure operation.
Therefore, as a method of substantially shortening the exposure
wavelength while substantially increasing (widening) the depth of
focus when compared with the depth of focus in the air, the
exposure apparatus that uses the immersion method has recently
begun to gather attention (refer to, for example, the pamphlet of
International Publication No. 2004/053955).
[0008] However, in the exposure apparatus using this liquid
immersion method or other exposure apparatus whose distance
(working distance) between the lower end surface of the projection
optical system and the wafer is small, it is difficult to place the
multipoint AF system in the vicinity of the projection optical
system. Meanwhile, in the exposure apparatus, in order to realize
exposure with high precision, realizing surface position control of
the wafer with high precision is required. Further, with the
stepper or the scanner or the like, position measurement of the
stage (the table) which holds a substrate (for example, a wafer)
subject to exposure is performed in general, using a laser
interferometer having a high resolution. However, the optical path
length of the laser interferometry beam which measures the position
of the stage is around several hundred mm or more, and furthermore,
due to finer patterns owing to higher integration of semiconductor
devices, position control of the stage with higher precision is
becoming required. Therefore, short-term variation of measurement
values which is caused by temperature fluctuation (air fluctuation)
of the atmosphere on the beam optical path of the laser
interferometer can no longer be ignored.
[0009] Therefore, it can be considered that position control of the
table in the optical axis direction and in a tilt direction with
respect to the surface orthogonal to the optical axis, including
the focus leveling control of the wafer during exposure, using a
detection device which detects the surface position information of
the table, is to be performed, separately from the interferometer,
or together with the interferometer. However, in such a case, the
position and the tilt of the table in the optical direction
covering the entire movement range at least at the time of exposure
of the table should be measurable, and in order to prevent a sudden
change in the position and attitude of the table during the
movement, for example, transition between detection values in
neighboring detecting positions will have to be performed
smoothly.
SUMMARY OF THE INVENTION
[0010] According to a first aspect of the present invention, there
is provided a first movable body drive method in which a movable
body is driven substantially along a two-dimensional plane, the
method comprising: a first process in which a position in a
direction perpendicular to the two-dimensional plane and a tilt
with respect to the two-dimensional plane of the movable body is
measured using a detection device that has a plurality of detection
positions and has a plurality of sensor heads which detect
positional information of a surface of the movable body
substantially parallel to the two-dimensional plane in the
direction perpendicular to the two-dimensional plane with a
reference plane parallel to the two-dimensional plane serving as a
reference; and a second process in which a set of sensor heads used
to control the position and attitude of the movable body is
switched to another set of sensor heads which include at least one
sensor head different from the set of sensor heads so that the
position in the direction perpendicular to the two-dimensional
plane and the tilt with respect to the two-dimensional plane of the
movable body are continuous before and after the switching.
[0011] According to this method, a detection device is used to
measure the position in a direction perpendicular to the
two-dimensional plane and tilt with respect to the two-dimensional
plane of the movable body. Further, a set of sensor heads used to
control the position and attitude of the movable body is switched
to another set of sensor heads which include at least one sensor
head different from the set of sensor heads so that the position in
the direction perpendicular to the two-dimensional plane and the
tilt with respect to the two-dimensional plane of the movable body
are continuous before and after the switching. Accordingly,
although the sensor head to be used is sequentially switched
according the XY position of the movable body, the position in the
direction perpendicular to the two-dimensional plane and tilt with
respect to the two-dimensional plane of the movable body are stored
before and after the switching, and it becomes possible to drive
the movable body with high precision.
[0012] According to a second aspect of the present invention, there
is provided a pattern formation method, comprising: a mount process
in which an object is mounted on a movable body that can move along
a movement plane; and a drive process in which the movable body is
driven by the movable body drive method according to the present
invention to form a pattern on the object.
[0013] According to this method, by forming a pattern on the object
mounted on the movable body which is driven with good precision
using the movable body drive methods of the present invention, it
becomes possible to form a pattern on the object with good
accuracy.
[0014] According to a third aspect of the present invention, there
is provided a device manufacturing method including a pattern
formation process, wherein in the pattern formation process, a
pattern is formed on an object using the pattern formation method
of the present invention.
[0015] According to a fourth aspect of the present invention, there
is provided an exposure method in which a pattern is formed on an
object by an irradiation of an energy beam wherein for relative
movement of the energy beam and the object, a movable body on which
the object is mounted is driven, using the movable body drive
method of the present invention.
[0016] According to this method, for relative movement between an
energy beam irradiated on the object and the object, the movable
body on which the object is mounted is driven with good precision,
using the movable body drive method of the present invention.
Accordingly, it becomes possible to form a pattern on the object
with good precision by scanning exposure.
[0017] According to a fifth aspect of the present invention, there
is provided a first movable body drive system in which a movable
body is driven along a substantially two-dimensional plane, the
system comprising: a detection device that has a plurality of
detection positions, and has a plurality of sensor heads which
detect positional information of a surface of the movable body
substantially parallel to the two-dimensional plane at each
detection point, in a direction perpendicular to the
two-dimensional plane with a reference plane parallel to the
two-dimensional plane serving as a reference; and a controller
which measures a position in the direction perpendicular to the
two-dimensional plane and a tilt with respect to the two
dimensional plane of the movable body, based on the output of the
plurality of sensor heads of the detection device, and also
switches a set of sensor heads used to control the position and
attitude of the movable body from the set of sensor heads to
another set of sensor heads including at least one different sensor
head from the set of sensor heads so that the position in the
direction perpendicular to the two-dimensional plane and the tilt
with respect to the two-dimensional plane of the movable body
becomes successive before and after the switching, during the
movement of the movable body.
[0018] According to this system, a detection device is used to
measure the position in a direction perpendicular to the
two-dimensional plane and tilt with respect to the two-dimensional
plane of the movable body. Further, the controller switches a set
of sensor heads used to control the position and attitude of the
movable body to another set of sensor heads which include at least
one sensor head different from the set of sensor heads so that the
position of the movable body in the direction perpendicular to the
two-dimensional plane and the tilt with respect to the
two-dimensional plane are continuous before and after the
switching. Accordingly, although the sensor head to be used is
sequentially switched according the XY position of the movable
body, the position in the direction perpendicular to the
two-dimensional plane and tilt with respect to the two-dimensional
plane of the movable body are stored before and after the
switching, and it becomes possible to drive the movable body with
high precision.
[0019] According to a sixth aspect of the present invention, there
is provided a pattern formation apparatus, comprising: a movable
body drive system according to the present invention which drives
the movable body on which an object is mounted for pattern
formation to the object; and a pattern generation system which
generates a pattern on the object.
[0020] According to this apparatus, by generating a pattern with a
patterning unit on the object on the movable body driven with good
precision by the movable body drive system of the present
invention, it becomes possible to form a pattern on the object with
good precision.
[0021] According to a seventh aspect of the present invention,
there is provided an exposure apparatus that forms a pattern on an
object by an irradiation of an energy beam, the apparatus
comprising: a patterning device that irradiates the energy beam on
the object; and a movable body drive system of the present
invention, whereby the movable body drive system drives the movable
body on which the object is mounted for relative movement of the
energy beam and the object.
[0022] According to this apparatus, for relative movement of the
energy beam irradiated on the object from the patterning device and
the object, the movable body on which the object is mounted is
driven by the movable body drive system of the present invention.
Accordingly, it becomes possible to form a pattern on the object
with good precision by scanning exposure.
[0023] According to an eighth aspect of the present invention,
there is provided a second movable body drive method in which a
movable body is driven substantially along a two-dimensional plane,
the method comprising: detecting a position of the movable body in
a direction perpendicular to the two-dimensional plane with a first
sensor of a plurality of sensors placed within an operating area of
the movable body, and controlling at least one of the position in
the perpendicular direction and a tilt with respect to the
two-dimensional plane of the movable body, and also obtaining
correction information to correct the detection results by a second
sensor using tilt information of the movable body with respect to
the two-dimensional plane obtained from detection results by the
first sensor, when starting a control using detection results by
the second sensor different from the first sensor of the plurality
of sensors, according to a movement of the two-dimensional plane of
the movable body.
[0024] According to a ninth aspect of the present invention, there
is provided a third movable body drive method to drive a movable
body at least in a two-dimensional plane, wherein positional
information of the movable body in a direction perpendicular to the
two-dimensional plane is detected by at least one of a plurality of
sensors having different detection points within the
two-dimensional plane, and on detecting positional information of
the movable body with the one sensor and a different sensor,
detection information and tilt information of the movable body with
respect to the two-dimensional plane of the one sensor are used,
according to a movement of the movable body.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] In the accompanying drawings;
[0026] FIG. 1 is a view schematically showing the configuration of
an exposure apparatus related to an embodiment;
[0027] FIG. 2 is a planar view showing a stage device in FIG.
1;
[0028] FIG. 3 is a planar view showing the placement of various
measuring apparatuses (such as encoders, alignment systems, a
multipoint AF system, and Z heads) that are equipped in the
exposure apparatus in FIG. 1;
[0029] FIG. 4A is a planar view showing a wafer stage, and
[0030] FIG. 4B is a schematic side view of a partially sectioned
wafer stage WST;
[0031] FIG. 5A is a planar view that shows a measurement stage MST,
and
[0032] FIG. 5B is a partially sectioned schematic side view that
shows measurement stage MST;
[0033] FIG. 6 is a block diagram showing a configuration of a
control system of the exposure apparatus related to an
embodiment;
[0034] FIG. 7 is a view schematically showing an example of a
configuration of a Z head;
[0035] FIG. 8A is a view showing an example of a focus sensor,
[0036] FIGS. 8B and 8C are views used to explain the shape and
function of a cylindrical lens in FIG. 8A;
[0037] FIG. 9A is a view showing a divided state of a detection
area of a tetrameric light receiving element,
[0038] FIGS. 9B, 9C, and 9D are views respectively showing a
cross-sectional shape of reflected beam LB2 on a detection surface
in a front-focused, an ideal focus, and a back-focused state;
[0039] FIGS. 10A to 10C are views used to explain focus mapping
performed in the exposure apparatus related to an embodiment;
[0040] FIGS. 11A and 11B are views used to explain focus
calibration performed in the exposure apparatus related to an
embodiment;
[0041] FIGS. 12A and 12B are views used to explain offset
correction among AF sensors performed in the exposure apparatus
related to an embodiment;
[0042] FIG. 13 is a view showing a state of the wafer stage and the
measurement stage where exposure to a wafer on the wafer stage is
performed by a step-and-scan method;
[0043] FIG. 14 is a view showing a state of both stages at the time
of unloading of the wafer (when the measurement stage reaches the
position where Sec-BCHK (interval) is performed);
[0044] FIG. 15 is a view showing a state of both stages at the time
of loading of the wafer;
[0045] FIG. 16 is a view showing a state of both stages at the time
of switching (when the wafer stage has moved to a position where
the former processing of Pri-BCHK is performed) from stage servo
control by the interferometer to stage servo control by the
encoder;
[0046] FIG. 17 is a view showing a state of the wafer stage and the
measurement stage when alignment marks arranged in three first
alignment shot areas are being simultaneously detected using
alignment systems AL1, AL2.sub.2 and AL2.sub.3;
[0047] FIG. 18 is a view showing a state of the wafer stage and the
measurement stage when the former processing of focus calibration
is being performed;
[0048] FIG. 19 is a view showing a state of the wafer stage and the
measurement stage when alignment marks arranged in five second
alignment shot areas are being simultaneously detected using
alignment systems AL1 and AL2.sub.1 to AL2.sub.4;
[0049] FIG. 20 is a view showing a state of the wafer stage and the
measurement stage when at least one of the latter processing of
Pri-BCHK and the latter processing of focus calibration is being
performed;
[0050] FIG. 21 is a view showing a state of the wafer stage and the
measurement stage when alignment marks arranged in five third
alignment shot areas are being simultaneously detected using
alignment systems AL1 and AL2.sub.1 to AL2.sub.4;
[0051] FIG. 22 is a view showing a state of the wafer stage and the
measurement stage when alignment marks arranged in three fourth
alignment shot areas are being simultaneously detected using
alignment systems AL1, AL2.sub.2 and AL2.sub.3;
[0052] FIG. 23 is a view showing a state of the wafer stage and the
measurement stage when the focus mapping has ended;
[0053] FIGS. 24A and 243 are views for explaining a computation
method of the Z position and the amount of tilt of wafer stage WST
using the measurement results of the Z heads;
[0054] FIGS. 25A and 25B are views showing the state of a switching
of the Z heads which oppose the Y scale, along with the movement of
the wafer stage;
[0055] FIGS. 26A to 26E are views for explaining the switching
procedure of the Z heads;
[0056] FIGS. 27A to 27C are views for explaining a return procedure
of the Z heads using two states, which are scale servo and focus
servo;
[0057] FIGS. 28A and 28B are views for explaining a switching
process of the Z heads used for position control of the wafer
table; and
[0058] FIG. 29 is a view conceptually showing position control of
wafer stage WST, uptake of a measurement value of the Z head, and
the switching timing of the Z head.
DESCRIPTION OF THE EMBODIMENTS
[0059] Hereinafter, an embodiment of the present invention will be
described, referring to FIGS. 1 to 29.
[0060] FIG. 1 shows a schematic configuration of an exposure
apparatus 100 in the embodiment. Exposure apparatus 100 is a
projection exposure apparatus of the step-and-scan method, namely
the so-called scanner. As it will be described later, a projection
optical system PL is arranged in the embodiment, and in the
description below, a direction parallel to an optical axis AX of
projection optical system PL will be described as the Z-axis
direction, a direction within a plane orthogonal to the Z-axis
direction in which a reticle and a wafer are relatively scanned
will be described as the Y-axis direction, a direction orthogonal
to the Z-axis and the Y-axis will be described as the X-axis
direction, and rotational (inclination) directions around the
X-axis, the Y-axis, and the Z-axis will be described as .theta.x,
.theta.y, and .theta.z directions, respectively.
[0061] Exposure apparatus 100 is equipped with an illumination
system 10, a reticle stage RST that holds a reticle R that is
illuminated by an illumination light for exposure (hereinafter,
referred to as illumination light, or exposure light) IL from
illumination system 10, a projection unit PU that includes
projection optical system PL that projects illumination light IL
emitted from reticle R on a wafer W, a stage device 50 that has a
wafer stage WST and a measurement stage MST, their control system,
and the like. On wafer stage WST, wafer W is mounted.
[0062] Illumination system 10 includes a light source, an
illuminance uniformity optical system, which includes an optical
integrator and the like, and an illumination optical system that
has a reticle blind and the like (none of which are shown), as is
disclosed in, for example, Kokai (Japanese Patent Unexamined
Application Publication) No. 2001-313250 (the corresponding U.S.
Patent Application Publication No. 2003/0025890) and the like.
Illumination system 10 illuminates a slit-shaped illumination area
IAR which is set on reticle R with a reticle blind (a masking
system) by illumination light (exposure light) IL with a
substantially uniform illuminance. In this case, as illumination
light IL, for example, an ArF excimer laser beam (wavelength 193
nm) is used. Further, as the optical integrator, for example, a
fly-eye lens, a rod integrator (an internal reflection type
integrator), a diffractive optical element or the like can be
used.
[0063] On reticle stage RST, reticle R on which a circuit pattern
or the like is formed on its pattern surface (the lower surface in
FIG. 1) is fixed, for example, by vacuum chucking. Reticle stage
RST is finely drivable or movable in within an XY plane by a
reticle stage drive section 11 (not shown in FIG. 1, refer to FIG.
6) that includes a linear motor or the like, and reticle stage RST
is also drivable in a scanning direction (in this case, the Y-axis
direction, which is the lateral direction of the page surface in
FIG. 1) at a designated scanning speed.
[0064] The positional information (including position (rotation)
information in the .theta.z direction) of reticle stage RST in the
XY plane (movement plane) is constantly detected, for example, at a
resolution of around 0.25 nm by a reticle laser interferometer
(hereinafter referred to as a "reticle interferometer") 116, via a
movable mirror 15 (the mirrors actually arranged are a Y movable
mirror (or a retro reflector) that has a reflection surface which
is orthogonal to the Y-axis direction and an X movable mirror that
has a reflection surface orthogonal to the X-axis direction). The
measurement values of reticle interferometer 116 are sent to a main
controller 20 (not shown in FIG. 1, refer to FIG. 6). Main
controller 20 computes the position of reticle stage RST in the
X-axis direction, Y-axis direction, and the .theta.z direction
based on the measurement values of reticle interferometer 116, and
also controls the position (and velocity) of reticle stage RST by
controlling reticle stage drive section 11 based on the computation
results. Incidentally, instead of movable mirror 15, the edge
surface of reticle stage RST can be mirror polished so as to form a
reflection surface (corresponding to the reflection surface of
movable mirror 15). Further, reticle interferometer 116 can measure
positional information of reticle stage RST related to at least one
of the Z-axis, .theta.x, or .theta.y directions.
[0065] Projection unit PU is placed below reticle stage RST in FIG.
1. Projection unit PU includes a barrel 40, and projection optical
system PL that has a plurality of optical elements which are held
in a predetermined positional relation inside barrel 40. As
projection optical system PL, for example, a dioptric system is
used, consisting of a plurality of lenses (lens elements) that is
disposed along an optical axis AX, which is parallel to the Z-axis
direction. Projection optical system PL is, for example, a
both-side telecentric dioptric system that has a predetermined
projection magnification (such as one-quarter, one-fifth, or
one-eighth times). Therefore, when illumination light IL from
illumination system 10 illuminates illumination area IAR, a reduced
image of the circuit pattern (a reduced image of a part of the
circuit pattern) of the reticle is formed within illumination area
IAR, with illumination light IL that has passed through reticle R
which is placed so that its pattern surface substantially coincides
with a first plane (an object plane) of projection optical system
PL, in an area conjugate to illumination area IAR on wafer W
(exposure area) whose surface is coated with a resist (a sensitive
agent) and is placed on a second plane (an image plane) side, via
projection optical system PL (projection unit PU). And by reticle
stage RST and wafer stage WST being synchronously driven, the
reticle is relatively moved in the scanning direction (the Y-axis
direction) with respect to illumination area IAR (illumination
light IL) while wafer W is relatively moved in the scanning
direction (the Y-axis direction) with respect to exposure area IA
(illumination light IL), thus scanning exposure of a shot area
(divided area) on wafer W is performed, and the pattern of the
reticle is transferred onto the shot area. That is, in the
embodiment, the pattern is generated on wafer W according to
illumination system 10, the reticle, and projection optical system
PL, and then by the exposure of the sensitive layer (resist layer)
on wafer W with illumination light IL, the pattern is formed on
wafer W.
[0066] Incidentally, although it is not shown, projection unit PU
is installed in a barrel platform supported by three struts via a
vibration isolation mechanism. However, as well as such a
structure, as is disclosed in, for example, the pamphlet of
International Publication WO2006/038952 and the like, projection
unit PU can be supported by suspension with respect to a mainframe
member (not shown) placed above projection unit PU or with respect
to a base member on which reticle stage RST is placed.
[0067] Incidentally, in exposure apparatus 100 of the embodiment,
because exposure is performed applying a liquid immersion method,
an opening on the reticle side becomes larger with the substantial
increase of the numerical aperture NA. Therefore, in order to
satisfy Petzval's condition and to avoid an increase in size of the
projection optical system, a reflection/refraction system (a
catodioptric system) which is configured including a mirror and a
lens can be employed as a projection optical system. Further, in
wafer W, in addition to a sensitive layer (a resist layer), for
example, a protection film (a topcoat film) or the like which
protects the wafer or a photosensitive layer can also be
formed.
[0068] Further, in exposure apparatus 100 of the embodiment, in
order to perform exposure applying the liquid immersion method, a
nozzle unit 32 that constitutes part of a local liquid immersion
device 8 is arranged so as to enclose the periphery of the lower
end portion of barrel 40 that holds an optical element that is
closest to an image plane side (wafer W side) that constitutes
projection optical system PL, which is a lens (hereinafter, also
referred to a "tip lens") 191 in this case. In the embodiment, as
shown in FIG. 1, the lower end surface of nozzle unit 32 is set to
be substantially flush with the lower end surface of tip lens 191.
Further, nozzle unit 32 is equipped with a supply opening and a
recovery opening of liquid Lq, a lower surface to which wafer W is
placed facing and at which the recovery opening is arranged, and a
supply flow channel and a recovery flow channel that are connected
to a liquid supply pipe 31A and a liquid recovery pipe 31B
respectively. Liquid supply pipe 31A and liquid recovery pipe 31B
are slanted by 45 degrees relative to an X-axis direction and
Y-axis direction in a planar view (when viewed from above) as shown
in FIG. 3, and are placed symmetric to a straight line (a reference
axis) LV which passes through the center (optical axis AX of
projection optical system PL, coinciding with the center of
exposure area IA previously described in the embodiment) of
projection unit PU and is also parallel to the Y-axis.
[0069] One end of a supply pipe (not shown) is connected to liquid
supply pipe 31A while the other end of the supply pipe is connected
to a liquid supply unit 5 (not shown in FIG. 1, refer to FIG. 6),
and one end of a recovery pipe (not shown) is connected to liquid
recovery pipe 31B while the other end of the recovery pipe is
connected to a liquid recovery device 6 (not shown in FIG. 1, refer
to FIG. 6).
[0070] Liquid supply device 5 includes a liquid tank for supplying
liquid, a compression pump, a temperature controller, a valve for
controlling supply/stop of the liquid to liquid supply pipe 31A,
and the like. As the valve, for example, a flow rate control valve
is preferably used so that not only the supply/stop of the liquid
but also the adjustment of flow rate can be performed. The
temperature controller adjusts the temperature of the liquid within
the tank, for example, to nearly the same temperature as the
temperature within the chamber (not shown) where the exposure
apparatus is housed. Incidentally, the tank, the compression pump,
the temperature controller, the valve, and the like do not all have
to be equipped in exposure apparatus 100, and at least part of them
can also be substituted by the equipment or the like available in
the plant where exposure apparatus 100 is installed.
[0071] Liquid recovery device 6 includes a liquid tank for
collecting liquid, a suction pump, a valve for controlling
recovery/stop of the liquid via liquid recovery pipe 31B, and the
like. As the valve, it is desirable to use a flow control valve
similar to the valve of liquid supply device 5. Incidentally, the
tank, the suction pump, the valve, and the like do not all have to
be equipped in exposure apparatus 100, and at least part of them
can also be substituted by the equipment or the like available in
the plant where exposure apparatus 100 is installed.
[0072] In the embodiment, as the liquid described above, pure water
(hereinafter, it will simply be referred to as "water" besides the
case when specifying is necessary) that transmits the ArF excimer
laser light (light with a wavelength of 193 nm) is to be used. Pure
water can be obtained in large quantities at a semiconductor
manufacturing plant or the like without difficulty, and it also has
an advantage of having no adverse effect on the photoresist on the
wafer, to the optical lenses or the like.
[0073] Refractive index n of the water with respect to the ArF
excimer laser light is around 1.44. In the water the wavelength of
illumination light IL is 193 nm.times.1/n, shorted to around 134
nm.
[0074] Liquid supply device 5 and liquid recovery device 6 each
have a controller, and the respective controllers are controlled by
main controller 20 (refer to FIG. 6). According to instructions
from main controller 20, the controller of liquid supply device 5
opens the valve connected to liquid supply pipe 31A to a
predetermined degree to supply liquid (water) to the space between
tip lens 191 and wafer W via liquid supply pipe 31A, the supply
flow channel and the supply opening. Further, when the water is
supplied, according to instructions from main controller 20, the
controller of liquid recovery device 6 opens the valve connected to
liquid recovery pipe 31B to a predetermined degree to recover the
liquid (water) from the space between tip lens 191 and wafer W into
liquid recovery device 6 (the liquid tank) via the recovery
opening, the recovery flow channel and liquid recovery pipe 31B.
During the supply and recovery operations, main controller 20 gives
commands to the controllers of liquid supply device 5 and liquid
recovery device 6 so that the quantity of water supplied to the
space between tip lens 191 and wafer W constantly equals the
quantity of water recovered from the space. Accordingly, a constant
quantity of liquid (water) Lq (refer to FIG. 1) is held in the
space between tip lens 191 and wafer W. In this case, liquid
(water) Lq held in the space between tip lens 191 and wafer W is
constantly replaced.
[0075] As is obvious from the above description, in the embodiment,
local liquid immersion device 8 is configured including nozzle unit
32, liquid supply device 5, liquid recovery device 6, liquid supply
pipe 31A and liquid recovery pipe 31B, and the like. Incidentally,
part of local liquid immersion device 8, for example, at least
nozzle unit 32 may also be supported in a suspended state by a main
frame (including the barrel platform) that holds projection unit
PU, or may also be arranged at another frame member that is
separate from the main frame. Or, in the case projection unit PU is
supported in a suspended state as is described earlier, nozzle unit
32 may also be supported in a suspended state integrally with
projection unit PU, but in the embodiment, nozzle unit 32 is
arranged on a measurement frame that is supported in a suspended
state independently from projection unit PU. In this case,
projection unit PU does not have to be supported in a suspended
state.
[0076] Incidentally, also in the case measurement stage MST is
located below projection unit PU, the space between a measurement
table (to be described later) and tip lens 191 can be filled with
water in the similar manner to the manner described above.
[0077] Incidentally, in the description above, one liquid supply
pipe (nozzle) and one liquid recovery pipe (nozzle) were arranged
as an example, however, the present invention is not limited to
this, and a configuration having multiple nozzles as is disclosed
in, for example, the pamphlet of International Publication No.
99/49504, may also be employed, in the case such an arrangement is
possible taking into consideration a relation with adjacent
members. The point is that any configuration can be employed, as
long as the liquid can be supplied in the space between optical
member (tip lens) 191 in the lowest end constituting projection
optical system PL and wafer W. For example, the liquid immersion
mechanism disclosed in the pamphlet of International Publication
No. 2004/053955, or the liquid immersion mechanism disclosed in the
EP Patent Application Publication No. 1 420 298 can also be applied
to the exposure apparatus of the embodiment.
[0078] Referring back to FIG. 1, stage device 50 is equipped with a
wafer stage WST and a measurement stage MST placed above a base
board 12, a measurement system 200 (refer to FIG. 6) which measures
positional information of the stages WST and MST, a stage drive
system 124 (refer to FIG. 6) which drives stages WST and MST and
the like. Measurement system 200 includes an interferometer system
118, an encoder system 150, and a surface position measurement
system 180 and the like as shown in FIG. 6. Incidentally, details
on the configuration and the like of interferometer system 118,
encoder system 150 and the like will be described later in the
description.
[0079] Referring back to FIG. 1, on the bottom surface of each of
wafer stage WST and measurement stage MST, a noncontact bearing
(not shown), for example, a vacuum preload type hydrostatic air
bearing (hereinafter, referred to as an "air pad") is arranged at a
plurality of points, and wafer stage WST and measurement stage MST
are supported in a noncontact manner via a clearance of around
several .mu.m above base board 12, by static pressure of
pressurized air that is blown out from the air pad toward the upper
surface of base board 12. Further, stages WST and MST are drivable
independently within the XY plane, by stage drive system 124 (refer
to FIG. 6) which includes a linear motor and the like.
[0080] Wafer stage WST includes a stage main section 91 and a wafer
table WTB that is mounted on stage main section 91. Wafer table WTB
and stage main section 91 are configured drivable in directions of
six degrees of freedom (X, Y, Z, .theta.x, .theta.y, and .theta.z)
with respect to base board 12 by a drive system including a linear
motor and a Z leveling mechanism (e.g., including a voice coil
motor and the like).
[0081] On wafer table WTB, a wafer holder (not shown) that holds
wafer W by vacuum suction or the like is arranged. The wafer holder
may also be formed integrally with wafer table WTB, but in the
embodiment, the wafer holder and wafer table WTB are separately
configured, and the wafer holder is fixed inside a recessed portion
of wafer table WTB, for example, by vacuum suction or the like.
Further, on the upper surface of wafer table WTB, a plate (liquid
repellent plate) 28 is arranged, which has the surface (liquid
repellent surface) substantially flush with the surface of wafer W
mounted on the wafer holder to which liquid repellent processing
with respect to liquid Lq is performed, has a rectangular outer
shape (contour), and has a circular opening that is formed in the
center portion and is slightly larger than the wafer holder (a
mounting area of the wafer). Plate 28 is made of materials with a
low coefficient of thermal expansion, such as glass or ceramics
(e.g., such as Zerodur (the brand name) of Schott AG,
Al.sub.2O.sub.3, or TiC), and on the surface of plate 28, a liquid
repellent film is formed by, for example, fluorine resin materials,
fluorine series resin materials such as polytetrafluoroethylene
(Teflon (registered trademark)), acrylic resin materials, or
silicon series resin materials. Further, as shown in a planer view
of wafer table WTB (wafer stage WST) in FIG. 4A, plate 28 has a
first liquid repellent area 28a whose outer shape (contour) is
rectangular enclosing a circular opening, and a second liquid
repellent area 28b that has a rectangular frame (annular) shape
placed around the first liquid repellent area 28a. On the first
liquid repellent area 28a, for example, at the time of an exposure
operation, at least part of a liquid immersion area 14 (for
example, refer to FIG. 13) that is protruded from the surface of
the wafer is formed, and on the second liquid repellent area 28b,
scales for an encoder system (to be described later) are formed.
Incidentally, at least part of the surface of plate 28 does not
have to be on a flush surface with the surface of the wafer, that
is, may have a different height from that of the surface of the
wafer. Further, plate 28 may be a single plate, but in the
embodiment, plate 28 is configured by combining a plurality of
plates, for example, the first and second liquid repellent plates
that correspond to the first liquid repellent area 28a and the
second liquid repellent area 28b respectively. In the embodiment,
water is used as liquid Lq as is described above, and therefore,
hereinafter the first liquid repellent area 28a and the second
liquid repellent area 28b are also referred to as a first water
repellent plate 28a and a second water repellent plate 28b.
[0082] In this case, exposure light IL is irradiated to the first
water repellent plate 28a on the inner side, while exposure light
IL is hardly irradiated to the second water repellent plate 28b on
the outer side. Taking this fact into consideration, in the
embodiment, a first water repellent area to which water repellent
coat having sufficient resistance to exposure light IL (light in a
vacuum ultraviolet region, in this case) is applied is formed on
the surface of the first water repellent plate 28a, and a second
water repellent area to which water repellent coat having
resistance to exposure light IL inferior to the first water
repellent area is applied is formed on the surface of the second
water repellent plate 28b. In general, since it is difficult to
apply water repellent coat having sufficient resistance to exposure
light IL (in this case, light in a vacuum ultraviolet region) to a
glass plate, it is effective to separate the water repellent plate
into two sections, the first water repellent plate 28a and the
second water repellent plate 28b which is the periphery of the
first water repellent plate, in the manner described above.
Incidentally, the present invention is not limited to this, and two
types of water repellent coat that have different resistance to
exposure light IL may also be applied on the upper surface of the
same plate in order to form the first water repellent area and the
second water repellent area. Further, the same kind of water
repellent coat may be applied to the first and second water
repellent areas. For example, only one water repellent area may
also be formed on the same plate.
[0083] Further, as is obvious from FIG. 4A, at the end portion on
the +Y side of the first water repellent plate 28a, a rectangular
cutout is formed in the center portion in the X-axis direction, and
a measurement plate 30 is embedded inside the rectangular space
(inside the cutout) that is enclosed by the cutout and the second
water repellent plate 28b. A fiducial mark FM is formed in the
center in the longitudinal direction of measurement plate 30 (on a
centerline LL of wafer table WTB), and a pair of aerial image
measurement slit patterns (slit-shaped measurement patterns) SL are
formed in the symmetrical placement with respect to the center of
the fiducial mark on one side and the other side in the X-axis
direction of fiducial mark FM. As each of aerial image measurement
slit patterns SL, an L-shaped slit pattern having sides along the
Y-axis direction and X-axis direction, or two linear slit patterns
extending in the X-axis and Y-axis directions respectively can be
used, as an example.
[0084] Then, as is shown in FIG. 4B, inside wafer stage WST below
each of aerial image measurement slit patterns SL, an L-shaped
housing 36 in which an optical system containing an objective lens,
a mirror, a relay lens and the like is housed is attached in a
partially embedded state penetrating through part of the inside of
wafer table WTB and stage main section 91. Housing 36 is arranged
in pairs corresponding to the pair of aerial image measurement slit
patterns SL, although omitted in the drawing.
[0085] The optical system inside housing 36 guides illumination
light IL that has been transmitted through aerial image measurement
slit pattern SL along an L-shaped route and emits the light toward
a -Y direction. Incidentally, in the following description, the
optical system inside housing 36 is described as a
light-transmitting system 36 by using the same reference code as
housing 36 for the sake of convenience.
[0086] Moreover, on the upper surface of the second water repellent
plate 28b, multiple grid lines are directly formed in a
predetermined pitch along each of four sides. More specifically, in
areas on one side and the other side in the X-axis direction of
second water repellent plate 28b (both sides in the horizontal
direction in FIG. 4A), Y scales 39Y.sub.1 and 39Y.sub.2 are formed
respectively, and Y scales 39Y.sub.1 and 39Y.sub.2 are each
composed of a reflective grating (for example, a diffraction
grating) having a periodic direction in the Y-axis direction in
which grid lines 38 having the longitudinal direction in the X-axis
direction are formed in a predetermined pitch along a direction
parallel to the Y-axis (the Y-axis direction).
[0087] Similarly, in areas on one side and the other side in the
Y-axis direction of second water repellent plate 28b (both sides in
the vertical direction in FIG. 4A), X scales 39X.sub.1 and
39X.sub.2 are formed respectively in a state where the scales are
placed between Y scales 39Y.sub.1 and 39Y.sub.2, and X scales
39X.sub.1 and 39X.sub.2 are each composed of a reflective grating
(for example, a diffraction grating) having a periodic direction in
the X-axis direction in which grid lines 37 having the longitudinal
direction in the Y-axis direction are formed in a predetermined
pitch along a direction parallel to the X-axis (the X-axis
direction). As each of the scales, a scale is used that has a
reflective diffraction grating made by, for example, hologram or
the like, on the surface of the second water repellent plate 28b.
In this case, each scale has gratings made up of narrow slits,
grooves or the like that are marked at a predetermined distance
(pitch) as graduations. The type of diffraction grating used for
each scale is not limited, and not only the diffraction grating
made up of grooves or the like that are mechanically formed, but
also, for example, the diffraction grating that is created by
exposing interference fringe on a photosensitive resin may be used.
However, each scale is created by marking the graduations of the
diffraction grating, for example, in a pitch between 138 nm to 4
.mu.m, for example, a pitch of 1 .mu.m on a thin plate shaped
glass. These scales are covered with the liquid repellent film
(water repellent film) described above. Incidentally, the pitch of
the grating is shown much wider in FIG. 4A than the actual pitch,
for the sake of convenience. The same is true also in other
drawings.
[0088] In this manner, in the embodiment, since the second water
repellent plate 28b itself constitutes the scales, a glass plate
with low-thermal expansion is to be used as the second water
repellent plate 28b. However, the present invention is not limited
to this, and a scale member made up of a glass plate or the like
with low-thermal expansion on which a grating is formed may also be
fixed on the upper surface of wafer table WTB, for example, by a
plate spring (or vacuum suction) or the like so as to prevent local
shrinkage/expansion. In this case, a water repellent plate to which
the same water repellent coat is applied on the entire surface may
be used instead of plate 28. Or, wafer table WTB may also be formed
by materials with a low coefficient of thermal expansion, and in
such a case, a pair of Y scales and a pair of X scales may be
directly formed on the upper surface of wafer table WTB.
[0089] Incidentally, in order to protect the diffraction grating,
it is also effective to cover the grating with a glass plate with
low thermal expansion that has water repellency (liquid
repellency). In this case, as the glass plate, a plate whose
thickness is the same level as the wafer, such as for example, a
plate 1 mm thick, can be used, and the plate is set on the upper
surface of wafer table WTB so that the surface of the glass plate
becomes the same height (flush) as the wafer surface.
[0090] Incidentally, a pattern for positioning is arranged for
deciding the relative position between an encoder head and a scale
near the edge of each scale (to be described later). The pattern
for positioning is configured, for example, from grid lines that
have different reflectivity, and when the encoder head scans the
pattern, the intensity of the output signal of the encoder changes.
Therefore, a threshold value is determined beforehand, and the
position where the intensity of the output signal exceeds the
threshold value is detected. Then, the relative position between
the encoder head and the scale is set, with the detected position
as a reference.
[0091] Further, to the -Y edge surface and the -X edge surface of
wafer table WTB, mirror-polishing is applied, respectively, and as
shown in FIG. 2, a reflection surface 17a and a reflection surface
17b are formed for interferometer system 118 which will be
described later in the description.
[0092] Measurement stage MST includes a stage main section 92
driven in the XY plane by a linear motor and the like (not shown),
and a measurement table MTB mounted on stage main section 92.
Measurement stage MST is configured drivable in at least directions
of three degrees of freedom (X, Y, and .theta.z) with respect to
base board 12 by a drive system (not shown).
[0093] Incidentally, the drive system of wafer stage WST and the
drive system of measurement stage MST are included in FIG. 6, and
are shown as stage drive system 124.
[0094] Various measurement members are arranged at measurement
table MTB (and stage main section 92). As such measurement members,
for example, as shown in FIGS. 2 and 5A, members such as an uneven
illuminance measuring sensor 94 that has a pinhole-shaped
light-receiving section which receives illumination light IL on an
image plane of projection optical system PL, an aerial image
measuring instrument 96 that measures an aerial image (projected
image) of a pattern projected by projection optical system PL, a
wavefront aberration measuring instrument 98 by the Shack-Hartman
method that is disclosed in, for example, the pamphlet of
International Publication No. 2003/065428 and the like are
employed. As wavefront aberration measuring instrument 98, the one
disclosed in, for example, the pamphlet of International
Publication No. 99/60361 (the corresponding EP Patent No. 1 079
223) can also be used.
[0095] As irregular illuminance sensor 94, the configuration
similar to the one that is disclosed in, for example, Kokai
(Japanese Unexamined Patent Application Publication) No. 57-117238
(the corresponding U.S. Pat. No. 4,465,368) and the like can be
used. Further, as aerial image measuring instrument 96, the
configuration similar to the one that is disclosed in, for example,
Kokai (Japanese Unexamined Patent Application Publication) No.
2002-014005 (the corresponding U.S. Patent Application Publication
No. 2002/0041377) and the like can be used. Incidentally, in the
embodiment, three measurement members (94, 96 and 98) were to be
arranged at measurement stage MST, however, the type of the
measurement member and/or the number is not limited to them. As the
measurement members, for example, measurement members such as a
transmittance measuring instrument that measures a transmittance of
projection optical system PL, and/or a measuring instrument that
observes local liquid immersion unit 8, for example, nozzle unit 32
(or tip lens 191) or the like may also be used. Furthermore,
members different from the measurement members such as a cleaning
member that cleans nozzle unit 32, tip lens 191 or the like may
also be mounted on measurement stage MST.
[0096] In the embodiment, as can be seen from FIG. 5A, the sensors
that are frequently used such as irregular illuminance sensor 94
and aerial image measuring instrument 96 are placed on a centerline
CL (Y-axis passing through the center) of measurement stage MST.
Therefore, in the embodiment, measurement using these sensors can
be performed by moving measurement stage MST only in the Y-axis
direction without moving the measurement stage in the X-axis
direction.
[0097] In addition to each of the sensors described above, an
illuminance monitor that has a light-receiving section having a
predetermined area size that receives illumination light IL on the
image plane of projection optical system PL may also be employed,
which is disclosed in, for example, Kokai (Japanese Unexamined
Patent Application Publication) No. 11-016816 (the corresponding
U.S. Patent Application Publication No. 2002/0061469) and the like.
The illuminance monitor is also preferably placed on the
centerline.
[0098] Incidentally, in the embodiment, liquid immersion exposure
is performed in which wafer W is exposed with exposure light
(illumination light) IL via projection optical system PL and liquid
(water) Lq, and accordingly irregular illuminance sensor 94 (and
the illuminance monitor), aerial image measuring instrument 96 and
wavefront aberration measuring instrument 98 that are used in
measurement using illumination light IL receive illumination light
IL via projection optical system PL and water. Further, only part
of each sensor such as the optical system may be mounted on
measurement table MTB (and stage main section 92), or the entire
sensor may be placed on measurement table MTB (and stage main
section 92).
[0099] Further, on the -Y edge surface and the -X edge surface of
measurement table MTB, reflection surfaces 19a and 19b are formed
similar to wafer table WTB previously described (refer to FIGS. 2
and 5A).
[0100] As shown in FIG. 5B, a frame-shaped attachment member 42 is
fixed to the end surface on the -Y side of stage main section 92 of
measurement stage MST. Further, to the end surface on the -Y side
of stage main section 92, a pair of photodetection systems 44 are
fixed in the vicinity of the center position in the X-axis
direction inside an opening of attachment member 42, in the
placement capable of facing a pair of light-transmitting systems 36
described previously. Each of photodetection systems 44 is composed
of an optical system such as a relay lens, a light receiving
element such as a photomultiplier tube, and a housing that houses
them. As is obvious from FIGS. 4B and 5B and the description so
far, in the embodiment, in a state where wafer stage WST and
measurement stage MST are closer together within a predetermined
distance in the Y-axis direction (including a contact state),
illumination light IL that has been transmitted through each aerial
image measurement slit pattern SL of measurement plate 30 is guided
by each light-transmitting system 36 and received by the
light-receiving element of each photodetection system 44. That is,
measurement plate 30, light-transmitting systems 36 and
photodetection systems 44 constitute an aerial image measuring unit
45 (refer to FIG. 6), which is similar to the one disclosed in
Kokai (Japanese Unexamined Patent Application Publication) No.
2002-014005 (the corresponding U.S. Patent Application Publication
No. 2002/0041377) referred to previously, and the like.
[0101] On attachment member 42, a fiducial bar (hereinafter,
shortly referred to as an "FD bar") which is made up of a
bar-shaped member having a rectangular sectional shape is arranged
extending in the X-axis direction. FD bar 46 is kinematically
supported on measurement stage MST by a full-kinematic mount
structure.
[0102] Since FD bar 46 serves as a prototype standard (measurement
standard), optical glass ceramics with a low coefficient of thermal
expansion, such as Zerodur (the brand name) of Schott AG are
employed as the materials. The flatness degree of the upper surface
(the surface) of FD bar 46 is set high to be around the same level
as a so-called datum plane plate. Further, as shown in FIG. 5A, a
reference grating (for example, a diffraction grating) 52 whose
periodic direction is the Y-axis direction is respectively formed
in the vicinity of the end portions on one side and the other side
in the longitudinal direction of FD bar 46. The pair of reference
gratings 52 is formed placed apart from each other at a
predetermined distance L, symmetric to the center in the X-axis
direction of FD bar 46, or more specifically, formed in a symmetric
placement to centerline CL previously described.
[0103] Further, on the upper surface of FD bar 46, a plurality of
reference marks M are formed in a placement as shown in FIG. 5A.
The plurality of reference marks M are formed in three-row arrays
in the Y-axis direction in the same pitch, and the array of each
row is formed being shifted from each other by a predetermined
distance in the X-axis direction. As each of reference marks M, a
two-dimensional mark having a size that can be detected by a
primary alignment system and secondary alignment systems (to be
described later) is used. Reference mark M may also be different in
shape (constitution) from fiducial mark FM, but in the embodiment,
reference mark M and fiducial mark FM have the same constitution
and also they have the same constitution with that of an alignment
mark of wafer W. Incidentally, in the embodiment, the surface of FD
bar 46 and the surface of measurement table MTB (which may include
the measurement members described above) are also covered with a
liquid repellent film (water repellent film) severally.
[0104] In exposure apparatus 100 of the embodiment, although it is
omitted in FIG. 1 from the viewpoint of avoiding intricacy of the
drawing, a primary alignment system AL1 having a detection center
at a position spaced apart from optical axis AX of projection
optical system PL at a predetermined distance on the -Y side is
actually placed on reference axis LV as shown in FIG. 3. Primary
alignment system AL1 is fixed to the lower surface of a main frame
(not shown) via a support member 54. On one side and the other side
in the X-axis direction with primary alignment system AL1 in
between, secondary alignment systems AL2.sub.1 and AL2.sub.2, and
AL2.sub.3 and AL2.sub.4 whose detection centers are substantially
symmetrically placed with respect to straight line LV are severally
arranged. That is, five alignment systems AL1 and AL2.sub.1 to
AL2.sub.4 are placed so that their detection centers are placed at
different positions in the X-axis direction, that is, placed along
the X-axis direction.
[0105] As is representatively shown by secondary alignment system
AL2.sub.4, each secondary alignment system AL2.sub.n (n=1 to 4) is
fixed to a tip (turning end) of an arm 56.sub.n (n=1 to 4) that can
turn around a rotation center O as the center in a predetermined
angle range in clockwise and anticlockwise directions in FIG. 3. In
the embodiment, a part of each secondary alignment system AL2.sub.n
(for example, including at least an optical system that irradiates
an alignment light to a detection area and also leads the light
that is generated from a subject mark within the detection area to
a light-receiving element) is fixed to arm 56.sub.n and the
remaining section is arranged at the main frame that holds
projection unit PU. The X-positions of secondary alignment systems
AL2.sub.3, AL2.sub.2, AL2.sub.3 and AL2.sub.4 are severally
adjusted by rotating around rotation center O as the center. In
other words, the detection areas (or the detection centers) of
secondary alignment systems AL2.sub.1, AL2.sub.2, AL2.sub.3, and
AL2.sub.4 are independently movable in the X-axis direction.
Accordingly, the relative positions of the detection areas of
primary alignment system AL1 and secondary alignment systems
AL2.sub.1, AL2.sub.2, AL2.sub.3, and AL2.sub.4 are adjustable in
the X-axis direction. Incidentally, in the embodiment, the
X-positions of secondary alignment systems AL2.sub.1, AL2.sub.2,
AL2.sub.3, and AL2.sub.4 are to be adjusted by the rotation of the
arms. However, the present invention is not limited to this, and a
drive mechanism that drives secondary alignment systems AL2.sub.1,
AL2.sub.2, AL2.sub.3, and AL2.sub.4 back and forth in the X-axis
direction may also be arranged. Further, at least one of secondary
alignment systems AL2.sub.1, AL2.sub.2, AL2.sub.3, and AL2.sub.4
can be moved not only in the X-axis direction but also in the
Y-axis direction. Incidentally, since part of each secondary
alignment system AL2.sub.n is moved by arm 56.sub.n, positional
information of the part that is fixed to arm 56.sub.n is measurable
by a sensor (not shown) such as, for example, an interferometer or
an encoder. The sensor may only measure position information in the
X-axis direction of secondary alignment system AL2.sub.n, or may
also be capable of measuring position information in another
direction, for example, the Y-axis direction and/or the rotation
direction (including at least one of the .theta.x and .theta.y
directions).
[0106] On the upper surface of each arm 56.sub.n, a vacuum pad
58.sub.n (n=1 to 4, not shown in FIG. 3, refer to FIG. 6) that is
composed of a differential evacuation type air bearing is arranged.
Further, arm 56.sub.n can be turned by a rotation drive mechanism
60.sub.n (n=1 to 4, not shown in FIG. 3, refer to FIG. 6) that
includes, for example, a motor or the like, in response to
instructions of main controller 20. Main controller 20 activates
each vacuum pad 58.sub.n to fix each arm 56.sub.n to a main frame
(not shown) by suction after rotation adjustment of arm 56.sub.n.
Thus, the state of each arm 56.sub.n after rotation angle
adjustment, that is, a desired positional relation between primary
alignment system AL1 and four secondary alignment systems AL2.sub.1
to AL2.sub.4 is maintained.
[0107] Incidentally, in the case a portion of the main frame facing
arm 56.sub.n is a magnetic body, an electromagnet may also be
employed instead of vacuum pad 58.
[0108] In the embodiment, as each of primary alignment system AL1
and four secondary alignment systems AL2.sub.1 to AL2.sub.4, for
example, an FIA (Field Image Alignment) system by an image
processing method is used that irradiates a broadband detection
beam that does not expose resist on a wafer to a subject mark, and
picks up an image of the subject mark formed on a light-receiving
plane by the reflected light from the subject mark and an image of
an index (an index pattern on an index plate arranged within each
alignment system) (not shown), using an imaging device (such as
CCD), and then outputs their imaging signals. The imaging signal
from each of primary alignment system AL1 and four secondary
alignment systems AL2.sub.1 to AL2.sub.4 is supplied to main
controller 20 in FIG. 6, via an alignment signal processing system
(not shown).
[0109] Incidentally, each of the alignment systems described above
is not limited to the FIA system, and an alignment sensor, which
irradiates a coherent detection light to a subject mark and detects
a scattered light or a diffracted light generated from the subject
mark or makes two diffracted lights (e.g. diffracted lights of the
same order or diffracted lights being diffracted in the same
direction) generated from the subject mark interfere and detects an
interference light, can naturally be used alone or in combination
as needed. Further, in the embodiment, five alignment systems AL1
and AL2.sub.1 to AL2.sub.4 are to be fixed to the lower surface of
the main frame that holds projection unit PU, via support member 54
or arm 56.sub.n. However, the present invention is not limited to
this, and for example, the five alignment systems may also be
arranged on the measurement frame described earlier.
[0110] Next, a configuration and the like of interferometer system
118 (refer to FIG. 6), which measures the positional information of
wafer stage WST and measurement stage MST, will be described.
[0111] The measurement principle of the interferometer will now be
briefly described, prior to describing a concrete configuration of
the interferometer system. The interferometer irradiates a
measurement beam (measurement light) on a reflection surface set at
a measurement object. The interferometer receives a synthesized
light of the reflected light and a reference beam, and measures the
intensity of interference light, which is the reflected light
(measurement light) and the reference beam made to interfere with
each other, with their polarized directions arranged. In this case,
due to optical path difference .DELTA.L of the reflected light and
the reference beam, the relative phase (phase difference) between
the reflected light and the reference beam changes by K.DELTA.L.
Accordingly, the intensity of the interference light changes in
proportion to 1+acos(K.DELTA.L). In this case, homodyne detection
is to be employed, and the wave number of the measurement light and
the reference beam is the same, expressed as K. Constant a is
decided by the intensity ratio of the measurement light and the
reference beam. In this case, the reflection surface to the
reference beam is arranged generally on the projection unit PU side
surface (in some cases, inside the interferometer unit). The
reflection surface of this reference beam becomes the reference
position of the measurement. Accordingly, in optical path
difference .DELTA.L, the distance from the reference position to
the reflection surface is reflected. Therefore, if the number of
times (the number of fringes) of intensity change of the
interference light with respect to the change of distance to the
reflection surface is measured, displacement of the reflection
surface provided in the measurement object can be computed by the
product of a counter value and a measurement unit. The measurement
unit, in the case of an interferometer of a single-pass method is
half the wavelength of the measurement light, and in the case of an
interferometer of the double-pass method, one-fourth of the
wavelength.
[0112] Now, in the case an interferometer of the heterodyne
detection method is employed, wave number K.sub.1 of the
measurement light and wave number K.sub.2 of the reference beam are
slightly different. In this case, when the optical path length of
the measurement light and the reference beam are L.sub.1 and
L.sub.2, respectively, the phase difference between the measurement
beam and the reference beam is given K.DELTA.L+.DELTA.KL.sub.1, and
the intensity of the interference light changes in proportion to
1+acos(K.DELTA.L+.DELTA.KL.sub.1). However, optical path difference
.DELTA.L=L.sub.1-L.sub.2, .DELTA.K=K.sub.1-K.sub.2, and K=K.sub.2.
When optical path L.sub.2 of the reference beam is sufficiently
short, and approximate .DELTA.L.apprxeq.L.sub.1 stands, the
intensity of the interference light changes in proportion to 1+acos
[(K+.DELTA.K).DELTA.L]. As it can be seen from above, the intensity
of the interference light periodically vibrates at a wavelength
2.pi./K of the reference beam along with the change of optical path
difference .DELTA.L, and the envelope curve of the periodic
vibration vibrates (beats) at a long cycle 2.pi./.DELTA.K.
Accordingly, in the heterodyne detection method, the changing
direction of optical path difference .DELTA.L, or more
specifically, the displacement direction of the measurement object
can be learned from the long-period beat.
[0113] Incidentally, as a major cause of error of the
interferometer, the effect of temperature fluctuation (air
fluctuation) of the atmosphere on the beam optical path can be
considered. Assume that wavelength .lamda. of the light changes to
.lamda.+.DELTA..lamda. by air fluctuation. Because the change of
phase difference KAI, by minimal change .DELTA..lamda. of the
wavelength is wave number K=2.pi./.lamda.,
2.pi..DELTA.L.DELTA..lamda./.lamda..sup.2 can be obtained. In this
case, when wavelength of light .lamda.=1 .mu.m and minute change
.DELTA..lamda.=1 nm, the phase change becomes 2.pi.100 with respect
to an optical path difference .DELTA.L=100 mm. This phase change
corresponds to displacement which is 100 times the measurement
unit. In the case the optical path length which is set is long as
is described, the interferometer is greatly affected by the air
fluctuation which occurs in a short time, and is inferior in
short-term stability. In such a case, it is desirable to use a
surface position measurement system which will be described later
that has an encoder or a Z head.
[0114] Interferometer system 118 includes a Y interferometer 16, X
interferometers 126, 127, and 128, and Z interferometers 43A and
43B for position measurement of wafer stage WST, and a Y
interferometer 18 and an X interferometer 130 for position
measurement of measurement stage MST, as shown in FIG. 2. By
severally irradiating a measurement beam on reflection surface 17a
and reflection surface 17b of wafer table WTB and receiving a
reflected light of each beam, Y interferometer 16 and X
interferometers 126, 127, and 128 (X interferometers 126 to 128 are
not shown in FIG. 1, refer to FIG. 2) measure a displacement of
each reflection surface from a reference position (for example, a
fixed mirror is placed on the side surface of projection unit PU,
and the surface is used as a reference surface), or more
specifically, measure the positional information of wafer stage WST
within the XY plane, and the positional information that has been
measured is supplied to main controller 20. In the embodiment, as
it will be described later on, as each interferometer a multiaxial
interferometer that has a plurality of measurement axes is used
with an exception for a part of the interferometers.
[0115] Meanwhile, to the side surface on the -Y side of stage main
section 91, a movable mirror 41 having the longitudinal direction
in the X-axis direction is attached via a kinematic support
mechanism (not shown), as shown in FIGS. 4A and 4B. Movable mirror
41 is made of a member which is like a rectangular solid member
integrated with a pair of triangular prisms adhered to a surface
(the surface on the -Y side) of the rectangular solid member. As it
can be seen from FIG. 2, movable mirror 41 is designed so that the
length in the X-axis direction is longer than reflection surface
17a of wafer table WTB by at least the spacing between the two Z
interferometers which will be described later.
[0116] To the surface on the -Y side of movable mirror 41,
mirror-polishing is applied, and three reflection surfaces 41b,
41a, and 41c are formed, as shown in FIG. 4B. Reflection surface
41a configures a part of the edge surface on the -Y side of movable
mirror 41, and reflection surface 41a is parallel with the XZ plane
and also extends in the X-axis direction. Reflection surface 41b
configures a surface adjacent to reflection surface 41a on the +Z
side, forming an obtuse angle to reflection surface 41a, and
spreading in the X-axis direction. Reflection surface 41c
configures a surface adjacent to the -Z side of reflection surface
41a, and is arranged symmetrically with reflection surface 41b,
with reflection surface 41b in between.
[0117] A pair of Z interferometers 43A and 43B (refer to FIGS. 1
and 2) that configures a part of interferometer system 118 (refer
to FIG. 6) and irradiates measurement beams on movable mirror 41 is
arranged facing movable mirror 41.
[0118] As it can be seen when viewing FIGS. 1 and 2 together, Z
interferometers 43A and 43B are placed apart on one side and the
other side of Y interferometer 16 in the X-axis direction at a
substantially equal distance and at positions slightly lower than Y
interferometer 16, respectively.
[0119] From each of the Z interferometers 43A and 43B, as shown in
FIG. 1, measurement beam B1 along the Y-axis direction is
irradiated toward reflection surface 41b, and measurement beam B2
along the Y-axis direction is irradiated toward reflection surface
41c (refer to FIG. 4B). In the embodiment, fixed mirror 478 having
a reflection surface orthogonal to measurement beam B1 reflected
off reflection surface 41b and a fixed mirror 47A having a
reflection surface orthogonal to measurement beam B2 reflected off
reflection surface 41c are arranged, each extending in the X-axis
direction at a position distanced apart from movable mirror 41 in
the -Y-direction by a predetermined distance in a state where the
fixed mirrors do not interfere with measurement beams 31 and
B2.
[0120] Fixed mirrors 47A and 473 are supported, for example, by the
same support body (not shown) arranged in the frame (not shown)
which supports projection unit PU.
[0121] Y interferometer 16, as shown in FIG. 2 (and FIG. 13),
irradiates measurement beams B4.sub.1 and B4.sub.2 on reflection
surface 17a of wafer table WTB along a measurement axis in the
Y-axis direction spaced apart by an equal distance to the -X side
and the +X side from reference axis LV previously described, and by
receiving each reflected light, detects the position of wafer table
WTB in the Y-axis direction (a Y position) at the irradiation point
of measurement beams B4.sub.1 and B4.sub.2. Incidentally, in FIG.
1, measurement beams B4.sub.1 and B4.sub.2 are representatively
shown as measurement beam 34.
[0122] Further, Y interferometer 16 irradiates a measurement beam
B3 toward reflection surface 41a along a measurement axis in the
Y-axis direction with a predetermined distance in the Z-axis
direction spaced between measurement beams B4.sub.1 and B4.sub.2,
and by receiving measurement beam B3 reflected off reflection
surface 41a, detects the Y position of reflection surface 41a (more
specifically wafer stage WST) of movable mirror 41.
[0123] Main controller 20 computes the Y position (or to be more
precise, displacement .DELTA.Y in the Y-axis direction) of
reflection surface 17a, or more specifically, wafer table WTB
(wafer stage WST), based on an average value of the measurement
values of the measurement axes corresponding to measurement beams
B4.sub.1 and B4.sub.2 of Y interferometer 16. Further, main
controller 20 computes displacement (yawing amount)
.DELTA..theta.z.sup.(Y) of wafer stage WST in the rotational
direction around the Z-axis (the .theta.z direction), based on a
difference of the measurement values of the measurement axes
corresponding to measurement beams B4.sub.1 and B4.sub.2. Further,
main controller 20 computes displacement (pitching amount)
.DELTA..theta.x in the .theta.x direction of wafer stage WST, based
on the Y position (displacement .DELTA.Y in the Y-axis direction)
of reflection surface 17a and reflection surface 41a.
[0124] Further, as shown in FIGS. 2 and 13, X interferometer 126
irradiates measurement beams B5.sub.1 and B5.sub.2 on wafer table
WTB along the dual measurement axes spaced apart from a straight
line (a reference axis) LH in the X-axis direction that passes the
optical axis of projection optical system PL by the same distance.
And, based on the measurement values of the measurement axes
corresponding to measurement beams B5.sub.1 and B5.sub.2, main
controller 20 computes a position (an X position, or to be more
precise, displacement .DELTA.X in the X-axis direction) of wafer
stage WST in the X-axis direction. Further, main controller 20
computes displacement (yawing amount) .DELTA..theta.z.sup.(X) of
wafer stage WST in the .theta.z direction from a difference of the
measurement values of the measurement axes corresponding to
measurement beams B5.sub.1 and B5.sub.2. Incidentally,
.DELTA..theta.z.sup.(X) obtained from X interferometer 126 and
.DELTA..theta.z.sup.(Y) obtained from Y interferometer 16 are equal
to each other, and represents displacement (yawing amount)
.DELTA..theta.z of wafer stage WST in the .theta.z direction.
[0125] Further, as shown in FIGS. 14 and 15, a measurement beam B7
from X interferometer 128 is irradiated on reflection surface 17b
of wafer table WTB along a straight line LUL, which is a line
connecting an unloading position UP where unloading of the wafer on
wafer table WTB is performed and a loading position LP where
loading of the wafer onto wafer table WTB is performed and is
parallel to the X-axis. Further, as shown in FIGS. 16 and 17, a
measurement beam B6 from X interferometer 127 is irradiated on
reflection surface 17b of wafer table WTB along a straight line LA,
which passes through the detection center of primary alignment
system AL1 and is parallel to the X-axis.
[0126] Main controller 20 can obtain displacement .DELTA.X of wafer
stage WST in the X-axis direction from the measurement values of
measurement beam 36 of X interferometer 127 and the measurement
values of measurement beam 37 of X interferometer 128. However, the
placement of the three X interferometers 126, 127, and 128 is
different in the Y-axis direction. Therefore, X interferometer 126
is used at the time of exposure as shown in FIG. 13, X
interferometer 127 is used at the time of wafer alignment as shown
in FIG. 19, and X interferometer 128 is used at the time of wafer
loading shown in FIG. 15 and wafer unloading shown in FIG. 14.
[0127] From Z interferometers 43A and 433 previously described,
measurement beams B1 and B2 that proceed along the Y-axis are
irradiated toward movable mirror 41, respectively, as shown in FIG.
1. These measurement beams B1 and 32 are incident on reflection
surfaces 41b and 41c of movable mirror 41, respectively, at a
predetermined angle of incidence (the angle is to be .theta./2).
Then, measurement beam B1 is sequentially reflected by reflection
surfaces 41b and 41c, and then is incident perpendicularly on the
reflection surface of fixed mirror 47B, whereas measurement beam B2
is sequentially reflected by reflection surfaces 41c and 41b and is
incident perpendicularly on the reflection surface of fixed mirror
47A. Then, measurement beams B2 and B1 reflected off the reflection
surface of fixed mirrors 47A and 47B are sequentially reflected by
reflection surfaces 41b and 41c again, or are sequentially
reflected by reflection surfaces 41c and 41b again (returning the
optical path at the time of incidence oppositely), and then are
received by Z interferometers 43A and 433.
[0128] In this case, when displacement of movable mirror 41 (more
specifically, wafer stage WST) in the Z-axis direction is .DELTA.Zo
and displacement in the Y-axis direction is .DELTA.Yo, an optical
path length change .DELTA.L1 of measurement beam B1 and an optical
path length change .DELTA.L2 of measurement beam B2 can
respectively be expressed as in formulas (1) and (2) below.
.DELTA.L1=.DELTA.Yo.times.(1+cos .theta.)+.DELTA.Zo.times.sin
.theta. (1)
.DELTA.L2=.DELTA.Yo.times.(1+cos .theta.)-.DELTA.Zo.times.sin
.theta. (2)
[0129] Accordingly, from formulas (1) and (2), .DELTA.Zo and
.DELTA.Yo can be obtained using the following formulas (3) and
(4).
.DELTA.Zo=(.DELTA.L1-.DELTA.L2)/2 sin .theta. (3)
.DELTA.Yo=(.DELTA.L1+.DELTA.L2)/{2(1+cos .theta.)} (4)
[0130] Displacements .DELTA.Zo and .DELTA.Yo above can be obtained
with Z interferometers 43A and 43B. Therefore, displacement which
is obtained using Z interferometer 43A is to be .DELTA.ZoR and
.DELTA.YoR, and displacement which is obtained using Z
interferometer 43B is to be .DELTA.ZoL and .DELTA.YoL. And the
distance between measurement beams B1 and B2 irradiated by Z
interferometers 43A and 43B, respectively, in the X-axis direction
is to be a distance D (refer to FIG. 2). Under such premises,
displacement (yawing amount) .DELTA..theta.z of movable mirror 41
(more specifically, wafer stage WST) in the .theta.z direction and
displacement (rolling amount) .DELTA..theta.y in the .theta.y
direction can be obtained by the following formulas (5) and
(6).
.DELTA..theta.z=tan.sup.-1{(.DELTA.YoR-.DELTA.YoL)/D} (5)
.DELTA..theta.y=tan.sup.-1{(.DELTA.ZoL-.DELTA.ZoR)/D} (6)
[0131] Accordingly, by using the formulas (3) to (6) above, main
controller 20 can compute displacement of wafer stage WST in four
degrees of freedom, .DELTA.Zo, .DELTA.Yo, .DELTA..theta.z, and
.DELTA..theta.y, based on the measurement results of Z
interferometers 43A and 43B.
[0132] In the manner described above, from the measurement results
of interferometer system 118, main controller 20 can obtain
displacement of wafer stage WST in directions of six degrees of
freedom (Z, X, Y, .theta.z, .theta.x, and .theta.y directions).
[0133] Incidentally, in the embodiment, a single stage which can be
driven in six degrees of freedom was employed as wafer stage WST,
however, instead of this, wafer stage WST can be configured
including a stage main section 91, which is freely movable within
the XY plane, and a wafer table WTB, which is mounted on stage main
section 91 and is finely drivable relatively with respect to stage
main section 91 in at least the Z-axis direction, the .theta.x
direction, and the .theta.y direction, or a wafer stage WST can be
employed that has a so-called coarse and fine movement structure
where wafer table WTB can be configured finely movable in the
X-axis direction, the Y-axis direction, and the .theta.z direction
with respect to stage main section 91. However, in this case, a
configuration in which positional information of wafer table WTB in
directions of six degree of can be measured by interferometer
system 118 will have to be employed. Also for measurement stage
MST, the stage can be configured similarly, by a stage main section
92, and a measurement table MTB, which is mounted on stage main
section 91 and has three degrees of freedom or six degrees of
freedom. Further, instead of reflection surface 17a and reflection
surface 17b, a movable mirror consisting of a plane mirror can be
arranged in wafer table WTB.
[0134] In the embodiment, however, position information within the
XY plane (including the rotation information in the .theta.z
direction) of wafer stage WST (wafer table WTB) is mainly measured
by an encoder system (to be described later), and the measurement
values of interferometers 16, 126, and 127 are secondarily used in
cases such as when long-term fluctuation (for example, by temporal
deformation or the like of the scales) of the measurement values of
the encoder system is corrected (calibrated).
[0135] Incidentally, at least part of interferometer system 118
(such as an optical system) may be arranged at the main frame that
holds projection unit PU, or may also be arranged integrally with
projection unit PU that is supported in a suspended state as is
described above, however, in the embodiment, interferometer system
118 is to be arranged at the measurement frame described above.
[0136] Incidentally, in the embodiment, positional information of
wafer stage WST was to be measured with a reflection surface of a
fixed mirror arranged in projection unit PU serving as a reference
surface, however, the position to place the reference surface at is
not limited to projection unit PU, and the fixed mirror does not
always have to be used to measure the positional information of
wafer stage WST.
[0137] Further, in the embodiment, positional information of wafer
stage WST measured by interferometer system 118 is not used in the
exposure operation and the alignment operation which will be
described later on, and was mainly to be used in calibration
operations (more specifically, calibration of measurement values)
of the encoder system, however, the measurement information (more
specifically, at least one of the positional information in
directions of five degrees of freedom) of interferometer system 118
can be used in the exposure operation and/or the alignment
operation. Further, using interferometer system 118 as a backup of
an encoder system can also be considered, which will be explained
in detail later on. In the embodiment, the encoder system measures
positional information of wafer stage WST in directions of three
degrees of freedom, or more specifically, the X-axis, the Y-axis,
and the .theta.z directions. Therefore, in the exposure operation
and the like, of the measurement information of interferometer
system 118, positional information related to a direction that is
different from the measurement direction (the X-axis, the Y-axis,
and the .theta.z direction) of wafer stage WST by the encoder
system, such as, for example, positional information related only
to the ex direction and/or the .theta.y direction can be used, or
in addition to the positional information in the different
direction, positional information related to the same direction
(more specifically, at least one of the X-axis, the Y-axis, and the
.theta.z directions) as the measurement direction of the encoder
system can also be used. Further, in the exposure operation and the
like, the positional information of wafer stage WST in the Z-axis
direction measured using interferometer system 118 can be used.
[0138] In addition, interferometer system 118 (refer to FIG. 6)
includes a Y interferometer 18 and an X interferometer 130 for
measuring the two-dimensional position coordinates of measurement
table MTB. Y interferometer 18 and X interferometer 130 (X
interferometer 130 is not shown in FIG. 1, refer to FIG. 2)
irradiate measurement beams on reflection surfaces 19a and 19b of
measurement table MTB as shown in FIG. 2, and measure the
displacement from a reference position of each reflection surface
by receiving the respective reflected lights. Main controller 20
receives the measurement values of Y interferometer 18 and X
interferometer 130, and computes the positional information (for
example, including at least the positional information in the
X-axis and the Y-axis directions and rotation information in the
.theta.z direction) of measurement stage MST.
[0139] Incidentally, as the Y interferometer used for measuring
measurement table MTB, a multiaxial interferometer which is similar
to Y interferometer 16 used for measuring wafer stage WST can be
used. Further, as the X interferometer used for measuring
measurement table MTB, a two-axis interferometer which is similar
to X interferometer 126 used for measuring wafer stage WST can be
used. Further, in order to measure Z displacement, Y displacement,
yawing amount, and rolling amount of measurement stage MST,
interferometers similar to Z interferometers 43A and 43B used for
measuring wafer stage WST can be introduced.
[0140] Next, the structure and the like of encoder system 150
(refer to FIG. 6) which measures positional information (including
rotation information in the .theta.z direction) of wafer stage WST
in the XY plane will be described.
[0141] In exposure apparatus 100 of the embodiment, as shown in
FIG. 3, four head units 62A to 62D of encoder system 150 are placed
in a state of surrounding nozzle unit 32 on all four sides. In
actual, head units 62A to 62D are fixed to the foregoing main frame
that holds projection unit PU in a suspended state via a support
member, although omitted in the drawings such as FIG. 3 from the
viewpoint of avoiding intricacy of the drawings.
[0142] As shown in FIG. 3, head units 62A and 62C are placed on the
+X side and the -X side of projection unit PU, with the X-axis
direction serving as a longitudinal direction. Head units 62A and
62C are each equipped with a plurality of (five, in this case) Y
heads 65.sub.i and 64.sub.j (i, j=1-5) that are placed at a
distance WD in the X-axis direction. More particularly, head units
62A and 62C are each equipped with a plurality of (four, in this
case) Y heads (64.sub.1 to 64.sub.4 or 65.sub.2 to 65.sub.5) that
are placed on straight line (reference axis) LH which passes
through optical axis AX of projection optical system PL and is also
parallel to the X-axis at distance WD except for the periphery of
projection unit PU, and a Y head (64.sub.5 or 65.sub.1) which is
placed at a position a predetermined distance away in the
-Y-direction from reference axis LH in the periphery of projection
unit PU, or more specifically, on the -Y side of nozzle unit 32.
Head units 62A and 62C are each also equipped with five Z heads
which will be described later on. Hereinafter, Y heads 65.sub.j and
64.sub.i will also be described as Y heads 65 and 64, respectively,
as necessary.
[0143] Head unit 62A constitutes a multiple-lens (five-lens, in
this case) Y linear encoder (hereinafter appropriately shortened to
"Y encoder" or "encoder") 70A (refer to FIG. 6) that measures the
position of wafer stage WST (wafer table WTB) in the Y-axis
direction (the Y-position) using Y scale 39Y.sub.1 previously
described. Similarly, head unit 62C constitutes a multiple-lens
(five-lens, in this case) Y linear encoder 70C (refer to FIG. 6)
that measures the Y-position of wafer stage WST (wafer table WTB)
using Y scale 39Y.sub.2 described above. In this case, distance WD
in the X-axis direction of the five Y heads (64.sub.i or 65.sub.j)
(more specifically, measurement beams) that head units 62A and 62C
are each equipped with, is set slightly narrower than the width (to
be more precise, the length of grid line 38) of Y scales 39Y.sub.1
and 39Y.sub.2 in the X-axis direction.
[0144] As shown in FIG. 3, head unit 62B is placed on the +Y side
of nozzle unit 32 (projection unit PU), and is equipped with a
plurality of, in this case, four X heads 66.sub.5 to 66.sub.8 that
are placed on reference axis LV previously described along Y-axis
direction at distance WD. Further, head unit 62D is placed on the
-Y side of primary alignment system AL1, on the opposite side of
head unit 62B via nozzle unit 32 (projection unit PU), and is
equipped with a plurality of, in this case, four X heads 66.sub.2
to 66.sub.4 that are placed on reference axis LV at distance WD.
Hereinafter, X heads 66.sub.1 to 66.sub.8 will also be described as
X head 66, as necessary.
[0145] Head unit 62B constitutes a multiple-lens (four-lens, in
this case) X linear encoder (hereinafter, shortly referred to as an
"X encoder" or an "encoder" as needed) 70B (refer to FIG. 6) that
measures the position in the X-axis direction (the X-position) of
wafer stage WST using X scale 39X.sub.1 described above. Further,
head unit 62D constitutes a multiple-lens (four-lens, in this case)
X encoder 70D (refer to FIG. 6) that measures the X-position of
wafer stage WST using X scale 39X.sub.2 described above.
[0146] Here, the distance between adjacent X heads 66 (measurement
beams) that are equipped in each of head units 62B and 62D is set
shorter than a width in the Y-axis direction of X scales 39X.sub.1
and 39X.sub.2 (to be more accurate, the length of grid line 37).
Further, the distance between X head 66 of head unit 62B farthest
to the -Y side and X head 66 of head unit 62D farthest to the +Y
side is set slightly narrower than the width of wafer stage WST in
the Y-axis direction so that switching (linkage described below)
becomes possible between the two X heads by the movement of wafer
stage WST in the Y-axis direction.
[0147] In the embodiment, furthermore, head units 62F and 62E are
respectively arranged a predetermined distance away on the -Y side
of head units 62A and 62C. Although illustration of head units 62E
and 62F is omitted in FIG. 3 and the like from the viewpoint of
avoiding intricacy of the drawings, in actual practice, head units
62E and 62F are fixed to the foregoing main frame that holds
projection unit PU in a suspended state via a support member.
Incidentally, for example, in the case projection unit PU is
supported in a suspended state, head units 62E and 62F, and head
units 62A to 62D which are previously described can be supported in
a suspended state integrally with projection unit PU, or can be
arranged at the measurement frame described above.
[0148] Head unit 62E is equipped with four Y heads 67.sub.1 to
67.sub.4 whose positions in the X-axis direction are different.
More particularly, head unit 62E is equipped with three Y heads
67.sub.1 to 67.sub.3 placed on the -X side of the secondary
alignment system AL2.sub.1 on reference axis LA previously
described at substantially the same distance as distance WD
previously described, and one Y head 67.sub.4 which is placed at a
position a predetermined distance (a distance slightly shorter than
WD) away on the +X side from the innermost (the +X side) Y head
67.sub.3 and is also on the +Y side of the secondary alignment
system AL2.sub.1 a predetermined distance away to the +Y side of
reference axis LA.
[0149] Head unit 62F is symmetrical to head unit 62E with respect
to reference axis LV, and is equipped with four Y heads 68.sub.1 to
68.sub.4 which are placed in symmetry to four Y heads 67.sub.1 to
67.sub.4 with respect to reference axis LV. Hereinafter, Y heads
67.sub.1 to 67.sub.4 and 68.sub.1 to 68.sub.4 will also be
described as Y heads 67 and 68, respectively, as necessary. In the
case of an alignment operation and the like which will be described
later on, at least one each of Y heads 67 and 68 faces Y scale
39Y.sub.2 and 39Y.sub.1, respectively, and by such Y heads 67 and
68 (more specifically, Y encoders 70C and 70A which are configured
by these Y heads 67 and 68), the Y position (and the .theta.z
rotation) of wafer stage WST is measured.
[0150] Further, in the embodiment, at the time of baseline
measurement (Sec-BCHK (interval)) and the like of the secondary
alignment system AL2.sub.1 which will be described later on, Y head
67.sub.3 and 68.sub.2 which are adjacent to the secondary alignment
systems AL2.sub.1 and AL2.sub.4 in the X-axis direction face the
pair of reference gratings 52 of FD bar 46, respectively, and by Y
heads 67.sub.3 and 68.sub.2 that face the pair of reference
gratings 52, the Y position of FD bar 46 is measured at the
position of each reference grating 52. In the description below,
the encoders configured by Y heads 67.sub.3 and 68.sub.2 which face
the pair of reference gratings 52, respectively, are referred to as
Y linear encoders (also shortly referred to as a "Y encoder" or an
"encoder" as needed) 70E.sub.2 and 70F.sub.2. Further, for
identification, Y encoders 70E and 70F configured by Y heads 67 and
68 that face Y scales 39Y.sub.2 and 39Y.sub.1 described above,
respectively, will be referred to as Y encoders 70E.sub.1 and
70F.sub.1.
[0151] The linear encoders 70A to 70F described above measure the
position coordinates of wafer stage WST at a resolution of, for
example, around 0.1 nm, and the measurement values are supplied to
main controller 20. Main controller 20 controls the position within
the XY plane of wafer stage WST based on three measurement values
of linear encoders 70A to 70D or on three measurement values of
encoders 70B, 70D, 70E.sub.1, and 70F.sub.1, and also controls the
rotation in the .theta.z direction of FD bar 46 based on the
measurement values of linear encoders 70E.sub.2 and 70F.sub.2.
[0152] In exposure apparatus 100 of the embodiment, as shown in
FIG. 3, a multipoint focal position detecting system (hereinafter,
shortly referred to as a "multipoint AF system") by an oblique
incident method is arranged, which is composed of an irradiation
system 90a and a photodetection system 90b, having a configuration
similar to the one disclosed in, for example, Kokai (Japanese
Unexamined Patent Application Publication) No. 06-283403 (the
corresponding U.S. Pat. No. 5,448,332) and the like. In the
embodiment, as an example, irradiation system 90a is placed on the
+Y side of the -X end portion of head unit 62E previously
described, and photodetection system 90b is placed on the +Y side
of the +X end portion of head unit 62F previously described in a
state opposing irradiation system 90a.
[0153] A plurality of detection points of the multipoint AF system
(90a, 90b) are placed at a predetermined distance along the X-axis
direction on the surface to be detected. In the embodiment, the
plurality of detection points are placed, for example, in the
arrangement of a matrix having one row and M columns (M is a total
number of detection points) or having two rows and N columns (N is
a half of a total number of detection points). In FIG. 3, the
plurality of detection points to which a detection beam is
severally irradiated are not individually shown, but are shown as
an elongate detection area (beam area) AF that extends in the
X-axis direction between irradiation system 90a and photodetection
system 90b. Because the length of detection area AF in the X-axis
direction is set to around the same as the diameter of wafer W, by
only scanning wafer W in the Y-axis direction once, position
information (surface position information) in the Z-axis direction
across the entire surface of wafer W can be measured. Further,
since detection area AF is placed between liquid immersion area 14
(exposure area IA) and the detection areas of the alignment systems
(AL1, AL2.sub.1 to AL2.sub.4) in the Y-axis direction, the
detection operations of the multipoint AF system and the alignment
systems can be performed in parallel. The multipoint AF system may
also be arranged on the main frame that holds projection unit PU or
the like, however, in the embodiment, the system will be arranged
on the measurement frame previously described.
[0154] Incidentally, the plurality of detection points are to be
placed in one row and M columns, or two rows and N columns, but the
numbers) of rows and/or columns is/are not limited to these
numbers. However, in the case the number of rows is two or more,
the positions in the X-axis direction of detection points are
preferably made to be different even between the different rows.
Moreover, the plurality of detection points is to be placed along
the X-axis direction. However, the present invention is not limited
to this, and all of or some of the plurality of detection points
may also be placed at different positions in the Y-axis direction.
For example, the plurality of detection points may also be placed
along a direction that intersects both of the X-axis and the
Y-axis. That is, the positions of the plurality of detection points
only have to be different at least in the X-axis direction.
Further, a detection beam is to be irradiated to the plurality of
detection points in the embodiment, but a detection beam may also
be irradiated to, for example, the entire area of detection area
AF. Furthermore, the length of detection area AF in the X-axis
direction does not have to be nearly the same as the diameter of
wafer W.
[0155] In the vicinity of detection points located at both ends out
of a plurality of detection points of the multipoint AF system
(90a, 90b), that is, in the vicinity of both end portions of beam
area AF, heads 72a and 72b, and 72c and 72d of surface position
sensors for Z position measurement (hereinafter, shortly referred
to as "Z heads") are arranged each in a pair, in symmetrical
placement with respect to reference axis LV. Z heads 72a to 72d are
fixed to the lower surface of a main frame (not shown).
Incidentally, Z heads 72a to 72d may also be arranged on the
measurement frame described above or the like.
[0156] As Z heads 72a to 72d, a sensor head that irradiates a light
to wafer table WTB from above, receives the reflected light and
measures position information of the wafer table WTB surface in the
Z-axis direction orthogonal to the XY plane at the irradiation
point of the light, as an example, a head of an optical
displacement sensor (a sensor head by an optical pickup method),
which has a configuration like an optical pickup used in a CD drive
device, is used.
[0157] Furthermore, head units 62A and 62C previously described are
respectively equipped with Z heads 76.sub.j and 74.sub.i (i,
j=1-5), which are five heads each, at the same X position as Y
heads 65.sub.j and 64.sub.i (i, j=1-5) that head units 62A and 62C
are respectively equipped with, with the Y position shifted. In
this case, Z heads 76.sub.3 to 76.sub.5 and 74.sub.1 to 74.sub.3,
which are three heads each on the outer side belonging to head
units 62A and 62C, respectively, are placed parallel to reference
axis LH a predetermined distance away in the +Y direction from
reference axis LH. Further, Z heads 76.sub.1 and 74.sub.5, which
are heads on the innermost side belonging to head units 62A and
62C, respectively, are placed on the +Y side of projection unit PU,
and Z heads 76.sub.2 and 74.sub.4, which are the second innermost
heads are placed on the -Y side of Y heads 65.sub.2 and 64.sub.4,
respectively. And Z heads 76.sub.j, 74.sub.i (i, j=1-5), which are
five heads each belonging to head unit 62A and 62C, respectively,
are placed symmetric to each other with respect to reference axis
LV. Incidentally, as each of the Z heads 76 and 74, an optical
displacement sensor head similar to Z heads 72a to 72d described
above is employed. Incidentally, the configuration and the like of
the Z heads will be described later on.
[0158] In this case, Z head 74.sub.3 is on a straight line parallel
to the Y-axis, the same as is with Z heads 72a and 72b previously
described. Similarly, Z head 76.sub.3 is on a straight line
parallel to the Y-axis, the same as is with Z heads 72c and 72d
previously described.
[0159] Z heads 72a to 72d, Z heads 74.sub.1 to 74.sub.5, and Z
heads 76.sub.1 to 76.sub.5 connect to main controller 20 via a
signal processing/selection device 170 as shown in FIG. 6, and main
controller 20 selects an arbitrary Z head from Z heads 72a to 72d,
Z heads 74.sub.1 to 74.sub.5, and Z heads 76.sub.1 to 76.sub.5 via
signal processing/selection device 170 and makes the head move into
an operating state, and then receives the surface position
information detected by the Z head which is in an operating state
via signal processing/selection device 170. In the embodiment, a
surface position measurement system 180 (a part of measurement
system 200) that measures positional information of wafer stage WST
in the Z-axis direction and the direction of inclination with
respect to the XY plane is configured, including Z heads 72a to
72d, Z heads 74.sub.1 to 74.sub.5, and Z heads 76.sub.1 to
76.sub.5, and signal processing/selection device 170.
[0160] Incidentally, in FIG. 3, measurement stage MST is omitted
and a liquid immersion area that is formed by water Lq held in the
space between measurement stage MST and tip lens 191 is shown by a
reference code 14. Further, in FIG. 3, a reference code UP
indicates an unloading position where a wafer on wafer table WTB is
unloaded, and a reference code LP indicates a loading position
where a wafer is loaded on wafer table WTB. In the embodiment,
unloading position UP and loading position LP are set symmetrically
with respect to reference axis LV. Incidentally, unloading position
UP and loading position LP may be the same position.
[0161] FIG. 6 shows the main configuration of the control system of
exposure apparatus 100. The control system is mainly configured of
main controller 20 composed of a microcomputer (or workstation)
that performs overall control of the entire apparatus. In memory 34
which is an external memory connected to main controller 20,
correction information is stored of measurement instrument systems
such as interferometer system 118, encoder system 150 (encoders 70A
to 70F), Z heads 72a to 72d, 74.sub.1 to 74.sub.5, 76.sub.1 to
76.sub.5 and the like. Incidentally, in FIG. 6, various sensors
such as irregular illuminance sensor 94, aerial image measuring
instrument 96 and wavefront aberration measuring instrument 98 that
are arranged at measurement stage MST are collectively shown as a
sensor group 99.
[0162] Next, the configuration and the like of Z heads 72a to 72d,
74.sub.1 to 74.sub.5, and 76.sub.1 to 76.sub.5 will be described,
focusing on Z head 72a shown in FIG. 7 as a representative.
[0163] As shown in FIG. 7, Z head 72a is equipped with a focus
sensor FS, a sensor main section ZH which houses focus sensor FS, a
drive section (not shown) which drives sensor main section ZH in
the Z-axis direction, a measurement section ZE which measures
displacement of sensor main section ZH in the Z-axis direction and
the like.
[0164] As focus sensor FS, an optical displacement sensor similar
to an optical pickup used in a CD drive unit that irradiates a
probe beam LB on a measurement target surface S and optically reads
the displacement of measurement surface S by receiving the
reflected light is used. The configuration and the like of the
focus sensor will be described later in the description. The output
signal of focus sensor FS is sent to the drive section (not
shown).
[0165] The drive section (not shown) includes an actuator such as,
for example, a voice coil motor, and one of a mover and a stator of
the voice coil motor is fixed to sensor main section ZH, and the
other is fixed to a part of a housing (not shown) which houses the
sensor main section ZH, measurement section ZE and the like,
respectively. The drive section drives sensor main section ZH in
the Z-axis direction according to the output signals from focus
sensor FS so that the distance between sensor main section ZH and
measurement target surface S is constantly maintained (or to be
more precise, so that measurement target surface S is maintained at
the best focus position of the optical system of focus sensor FS).
By this drive, sensor main section ZH follows the displacement of
measurement target surface S in the Z-axis direction, and a focus
lock state is maintained.
[0166] As measurement section ZE, in the embodiment, an encoder by
the diffraction interference method is used as an example.
Measurement section ZE includes a reflective diffraction grating EG
whose periodic direction is the Z-axis direction arranged on a side
surface of a support member SM fixed on the upper surface of sensor
main section ZH extending in the Z-axis direction, and an encoder
head EH which is attached to the housing (not shown) facing
diffraction grating EG. Encoder head EH reads the displacement of
sensor main section ZH in the Z-axis direction by irradiating probe
beam EL on diffraction grating EG, receiving the
reflection/diffraction light from diffraction grating EG with a
light-receiving element, and reading the deviation of an
irradiation point of probe beam EL from a reference point (for
example, the origin).
[0167] In the embodiment, in the focus lock state, sensor main
section ZH is displaced in the Z-axis direction so as to constantly
maintain the distance with measurement target surface S as
described above. Accordingly, by encoder head EH of measurement
section ZE measuring the displacement of sensor main section ZH in
the Z-axis direction, surface position (Z position) of measurement
target surface S is measured. Measurement values of encoder head EH
is supplied to main controller 20 via signal processing/selection
device 170 previously described as measurement values of Z head
72a.
[0168] As shown in FIG. 8A, as an example, focus sensor FS includes
three sections, an irradiation system FS.sub.1, an optical system
FS.sub.2, and a photodetection system FS.sub.3.
[0169] Irradiation system FS.sub.1 includes, for example, a light
source LD made up of laser diodes, and a diffraction grating plate
(a diffractive optical element) ZG placed on the optical path of a
laser beam outgoing from light source LD.
[0170] Optical system FS.sub.2 includes, for instance, a
diffraction light of the laser beam generated in diffraction
grating plate ZG, or more specifically, a polarization beam
splitter PBS, a collimator lens CL, a quarter-wave plate (a
.lamda./4 plate) WP, and object lens OL and the like placed
sequentially on the optical path of probe beam LB.sub.1.
[0171] Photodetection system FS.sub.3, for instance, includes a
cylindrical lens CYL and a tetrameric light receiving element ZD
placed sequentially on a return optical path of reflected beam
LB.sub.2 of probe beam LB.sub.1 on measurement target surface
S.
[0172] According to focus sensor FS, the linearly polarized laser
beam generated in light source LD of irradiation system FS.sub.1 is
irradiated on diffraction grating plate ZG, and diffraction light
(probe beam) LB.sub.1 is generated in diffraction grating plate ZG.
The central axis (principal ray) of probe beam LB.sub.1 is parallel
to the Z-axis and is also orthogonal to measurement target surface
S.
[0173] Then, probe beam LB.sub.1, or more specifically, light
having a polarization component that is a P-polarized light with
respect to a separation plane of polarization beam splitter PBS, is
incident on optical system FS.sub.2. In optical system FS.sub.2,
probe beam LB.sub.1 passes through polarization beam splitter PBS
and is converted into a parallel beam at collimator lens CL, and
then passes through .lamda./4 plate WP and becomes a circular
polarized light, which is condensed at object lens OL and is
irradiated on measurement target surface S. Accordingly, at
measurement target surface S, reflected light (reflected beam)
LB.sub.2 occurs, which is a circular polarized light that proceeds
inversely to the incoming light of probe beam LB.sub.1. Then,
reflected beam LB.sub.2 traces the optical path of the incoming
light (probe beam LB.sub.1) the other way around, and passes
through object lens OL, .lamda./4 plate WP, collimator lens CL, and
then proceeds toward polarization beam splitter PBS. In this case,
because the beam passes through .lamda./4 plate WP twice, reflected
beam LB.sub.2 is converted into an S-polarized light. Therefore,
the proceeding direction of reflected beam LB.sub.2 is bent at the
separation plane of polarization beam splitter PBS, so that it
moves toward photodetection system FS.sub.3.
[0174] In photodetection system FS.sub.3, reflected beam LB.sub.2
passes through cylindrical lenses CYL and is irradiated on a
detection surface of tetrameric light receiving element ZD. In this
case, cylindrical lenses CYL is a "cambered type" lens, and as
shown in FIG. 8B, the YZ section has a convexed shape with the
convexed section pointing the Y-axis direction, and as shown also
in FIG. 8C, the XY section has a rectangular shape. Therefore, the
sectional shape of reflected beam LB.sub.2 which passes through
cylindrical lenses CYL is narrowed asymmetrically in the Z-axis
direction and the X-axis direction, which causes astigmatism.
[0175] Tetrameric light receiving element ZD receives reflected
beam LB.sub.2 on its detection surface. The detection surface of
tetrameric light receiving element ZD has a square shape as a
whole, as shown in FIG. 9A, and it is divided equally into four
detection areas a, b, c, and d with the two diagonal lines serving
as a separation line. The center of the detection surface will be
referred to as O.sub.ZD.
[0176] In this case, in an ideal focus state (a state in focus)
shown in FIG. 8A, or more specifically, in a state where probe beam
LB.sub.1 is focused on measurement target surface S.sub.0, the
cross-sectional shape of reflected beam LB.sub.2 on the detection
surface becomes a circle with center O.sub.ZD serving as a center,
as shown in FIG. 9C.
[0177] Further, in the so-called front-focused state (more
specifically, a state equivalent to a state where measurement
target surface S is at ideal position S.sub.0 and tetrameric light
receiving element ZD is at a position shown by reference code 1 in
FIGS. 88 and 8C) where probe beam LB.sub.1 focuses on measurement
target surface S.sub.1 in FIG. 8A, the cross-sectional shape of
reflected beam LB.sub.2 on the detection surface becomes a
horizontally elongated circle with center O.sub.ZD serving as a
center as shown in FIG. 98.
[0178] Further, in the so-called back-focused state (more
specifically, a state equivalent to a state where measurement
target surface S is at ideal position S.sub.0 and tetrameric light
receiving element ZD is at a position shown by reference code-1 in
FIGS. 8B and 8C) where probe beam LB.sub.1 focuses on measurement
target surface S.sub.-1 in FIG. 8A, the cross-sectional shape of
reflected beam LB.sub.2 on the detection surface becomes a
longitudinally elongated circle with center O.sub.ZD serving as a
center as shown in FIG. 9D.
[0179] In an operational circuit (not shown) connected to
tetrameric light receiving element ZD, a focus error I expressed as
in the following formula (7) is computed and output to the drive
section (not shown), with the intensity of light received in the
four detection areas a, b, c, and d expressed as Ia, Ib, Ic, and
Id, respectively.
I=(Ia+Ic)-(Ib+Id) (7)
[0180] Incidentally, in the ideal focus state described above,
because the area of the beam cross-section in each of the four
detection areas is equal to each other, focus error I=0 can be
obtained. Further, in the front focused state described above,
according to formula (7), focus error becomes I<0, and in the
back focused state, according to formula (7), focus error becomes
I>0.
[0181] The drive section (not shown) receives focus error I from a
detection section FS.sub.3 within focus sensor FS, and drives
sensor main section ZH which stored focus sensor FS in the Z-axis
direction so as to reproduce I=0. By this operation of the drive
section, because sensor main section ZH is also displaced following
measurement target surface S, the probe beam focuses on measurement
target surface S without fail, or more specifically, the distance
between sensor main section ZH and measurement target surface S is
always constantly maintained (focus lock state is maintained).
[0182] Meanwhile, the drive section (not shown) can also drive and
position sensor main section ZH in the Z-axis direction so that a
measurement result of measurement section ZE coincides with an
input signal from the outside of Z head 72a. Accordingly, the focus
of probe beam LB can also be positioned at a position different
from the actual surface position of measurement target surface S.
By this operation (scale servo control) of the drive section,
processes such as return processing in the switching of the Z
heads, avoidance process at the time of abnormality generation in
the output signals and the like can be performed.
[0183] In the embodiment, as is previously described, an encoder is
adopted as measurement section ZE, and encoder head EH is used to
read the Z displacement of diffraction grating EG set in sensor
main section ZH. Because encoder head EH is a relative position
sensor which measures the displacement of the measurement object
(diffraction grating EG) from a reference point, it is necessary to
determine the reference point. In the embodiment, the reference
position (for example, the origin) of the Z displacement can be
determined by detecting an edge section of diffraction grating EG,
or in the case a lay out pattern is arranged in diffraction grating
EG, by detecting the pattern for positioning. In any case,
reference surface position of measurement target surface S can be
determined in correspondence with the reference position of
diffraction grating EG, and the Z displacement of measurement
target surface S from the reference surface position, or more
specifically, the position in the Z-axis direction can be measured.
Incidentally, at the start up and the like of the Z head, such as
the start up and the like of exposure apparatus 100, setting of the
reference position (for example, the origin, or more specifically,
the reference surface position of measurement target surface S) of
diffraction grating EG is executed without fail. In this case,
because it is desirable for the reference position to be set close
to the center of the movement range of sensor main section ZH, a
drive coil for adjusting the focal position of the optical system
can be arranged to adjust the Z position of object lens OL so that
the reference surface position corresponding to the reference
position around the center coincides with the focal position of the
optical system in the focus sensor FS.
[0184] In Z head 72a, because sensor main section ZH and
measurement section ZE are housed together inside the housing (not
shown) and the part of the optical path length of probe beam
LB.sub.1 which is exposed outside the housing is extremely short,
the influence of air fluctuation is extremely small. Accordingly,
even when compared, for example, with a laser interferometer, the
sensor including the Z head is much more superior in measurement
stability (short-term stability) during a period as short as while
the air fluctuates.
[0185] The other Z heads are also configured and function in a
similar manner as Z head 72a described above. As is described, in
the embodiment, as each z head, a configuration is employed where
the diffraction grating surfaces of Y scales 39Y.sub.1, 39Y.sub.2
and the like are observed from above (the +Z direction) as in the
encoder. Accordingly, by measuring the surface position information
of the upper surface of wafer table WTB at different positions with
the plurality of Z heads, the position of wafer stage WST in the
Z-axis direction, the .theta.y rotation (rolling), and the .theta.x
rotation (pitching) can be measured. However, in the embodiment,
because the accuracy of pitching control of wafer stage WST is not
especially important on exposure, the surface position measurement
system including the Z head does not measure pitching, and a
configuration was employed where one Z head each faces Y scales
39Y.sub.1 and 39Y.sub.2.
[0186] Next, detection of position information (surface position
information) of the wafer W surface in the Z-axis direction
(hereinafter, referred to as focus mapping) that is performed in
exposure apparatus 100 of the embodiment will be described.
[0187] On this focus mapping, as is shown in FIG. 10A, main
controller 20 controls the position within the XY plane of wafer
stage WST based on X head 66.sub.3 facing X scale 39X.sub.2 (X
linear encoder 70D) and two Y heads 68.sub.2 and 67.sub.3 facing Y
scales 39Y.sub.1 and 39Y.sub.2 respectively (Y linear encoders 70A
and 70C). In the state of FIG. 10A, a straight line (centerline)
parallel to the Y-axis that passes through the center of wafer
table WTB (which substantially coincides with the center of wafer
W) coincides with reference line LV previously described. Further,
although it is omitted in the drawing here, measurement stage MST
is located on the +Y side of wafer stage WST, and water is retained
in the space between FD bar 46, wafer table WTB and tip lens 191 of
projection optical system PL previously described (refer to FIG.
18).
[0188] Then, in this state, main controller 20 starts scanning of
wafer stage WST in the +Y direction, and after having started the
scanning, activates (turns ON) both Z heads 72a to 72d and the
multipoint AF system (90a, 90b) by the time when wafer stage WST
moves in the +Y direction and detection beams (detection area AF)
of the multipoint AF system (90a, 90b) begin to be irradiated on
wafer W.
[0189] Then, in a state where Z heads 72a to 72d and the multipoint
AF system (90a, 90b) simultaneously operate, as is shown in FIG.
10B, position information (surface position information) of the
wafer table WTB surface (surface of plate 28) in the Z-axis
direction that is measured by Z heads 72a to 72d and position
information (surface position information) of the wafer W surface
in the Z-axis direction at a plurality of detection points that is
detected by the multipoint AF system (90a, 90b) are loaded at a
predetermined sampling interval while wafer stage WST is proceeding
in the +Y direction, and three kinds of information, which are each
surface position information that has been loaded and the
measurement values of Y linear encoders 70F.sub.1 and 70E.sub.1 at
the time of each sampling, are made to correspond to one another
and are sequentially stored in a memory (not shown).
[0190] Then, when the detection beams of the multipoint AF system
(90a, 90b) begin to miss wafer W, main controller 20 ends the
sampling described above and converts the surface position
information at each detection point of the multipoint AF system
(90a, 90b) into data which uses the surface position information by
Z heads 72a to 72d that has been loaded simultaneously as a
reference.
[0191] More specifically, based on an average value of the
measurement values of Z heads 72a and 72b, surface position
information at a predetermined point (for example, corresponding to
a midpoint of the respective measurement points of Z heads 72a and
72b, that is, a point on substantially the same X-axis as the array
of a plurality of detection points of the multipoint AF system
(90a, 90b): hereinafter, this point is referred to as a left
measurement point P1) on an area (an area where Y scale 39Y.sub.2
is formed) near the edge section on the -X side of plate 28 is
obtained. Further, based on an average value of the measurement
values of Z heads 72c and 72d, surface position information at a
predetermined point (for example, corresponding to a midpoint of
the respective measurement points of Z heads 72c and 72d, that is,
a point on substantially the same X-axis as the array of a
plurality of detection points of the multipoint AF system (90a,
90b): hereinafter, this point is referred to as a right measurement
point P2) on an area (an area where Y scale 39Y.sub.1 is formed)
near the edge section on the +X side of plate 28 is obtained. Then,
as shown in FIG. 10C, main controller 20 converts the surface
position information at each detection point of the multipoint AF
system (90a, 90b) into surface position data z1-zk, which uses a
straight line that connects the surface position of left
measurement point P1 and the surface position of right measurement
point P2 as a reference. Main controller 20 performs such a
conversion on all information taken in during the sampling.
[0192] By obtaining such converted data in advance in the manner
described above, for example, in the case of exposure, main
controller 20 measures the wafer table WTB surface (a point on the
area where Y scale 39Y.sub.2 is formed (a point near left
measurement point P1 described above) and a point on the area where
Y scale 39Y.sub.1 is formed (a point near right measurement point
P1 described above)) with Z heads 74.sub.i and 76.sub.j previously
described, and computes the Z position and .theta.y rotation
(rolling) amount .theta.y of wafer stage WST. Then, by performing a
predetermined operation using the Z position, the rolling amount
.theta.y, and the .theta.x rotation (pitching) amount .theta.x of
wafer stage WST measured with Y interferometer 16, and computing
the Z position (Z0), rolling amount .theta.y, and pitching amount
.theta.x of the wafer table WTB surface in the center (the exposure
center) of exposure area IA previously described, and then
obtaining the straight line passing through the exposure center
that connects the surface position of left measurement point P1 and
the surface position of right measurement point P2 described above
based on the computation results, it becomes possible to perform
the surface position control (focus leveling control) of the upper
surface of wafer W without actually acquiring the surface position
information of the wafer W surface by using such straight line and
surface position data z1-zk. Accordingly, because there is no
problem even if the multipoint AF system is placed at a position
away from projection optical system PL, the focus mapping of the
embodiment can suitably be applied also to an exposure apparatus
and the like that has a short working distance.
[0193] Incidentally, in the description above, while the surface
position of left measurement point P1 and the surface position of
right measurement point P2 were computed based on the average value
of the measurement values of Z heads 72a and 72b, and the average
value of Z heads 72c and 72d, respectively, the surface position
information at each detection point of the multipoint AF system
(90a, 90b) can also be converted, for example, into surface
position data which uses the straight line connecting the surface
positions measured by Z heads 72a and 72c as a reference. In this
case, the difference between the measurement value of Z head 72a
and the measurement value of Z head 72b should be obtained at each
sampling timing, and the difference between the measurement value
of Z head 72c and the measurement value of Z head 72d obtained at
each sampling timing are to be obtained severally in advance. Then,
when performing surface position control at the time of exposure or
the like, by measuring the wafer table WTB surface with Z heads
74.sub.i and 76.sub.j and computing the Z-position and the .theta.y
rotation of wafer stage WST, and performing a predetermined
operation using these computed values, pitching amount .theta.x of
wafer stage WST measured by Y interferometer 16, surface position
data z1 to zk previously described, and the differences described
above, it becomes possible to perform surface position control of
wafer W, without actually obtaining the surface position
information of the wafer surface.
[0194] However, the description so far is made assuming that
unevenness does not exist on the wafer table WTB surface in the
X-axis direction. Accordingly, hereinafter, to simplify the
description, unevenness is not to exist on the wafer table WTB
surface in the X-axis direction and the Y-axis direction.
[0195] Next, focus calibration will be described. Focus calibration
refers to a process where a processing of obtaining a relation
between surface position information of wafer table WTB at end
portions on one side and the other side in the X-axis direction in
a reference state and detection results (surface position
information) at representative detection points on the measurement
plate 30 surface of multipoint AF system (90a, 90b) (former
processing of focus calibration), and a processing of obtaining
surface position information of wafer table WTB at end portions on
one side and the other side in the X-axis direction that correspond
to the best focus position of projection optical system PL detected
using aerial image measurement device 45 in a state similar to the
reference state above (latter processing of focus calibration) are
performed, and based on these processing results, an offset of
multipoint AF system (90a, 90b) at representative detection points,
or in other words, a deviation between the best focus position of
projection optical system PL and the detection origin of the
multipoint AF system, is obtained.
[0196] On the focus calibration, as is shown in FIG. 11A, main
controller 20 controls the position within the XY plane of wafer
stage WST based on X head 66.sub.2 facing X scale 39X.sub.2 (X
linear encoder 70D) and two Y heads 68.sub.2 and 67.sub.3 facing Y
scales 39Y.sub.1 and 39Y.sub.2 respectively (Y linear encoders 70A
and 70C). The state of FIG. 11A is substantially the same as the
state in 10A previously described. However, in the state of FIG.
11A, wafer table WTB is at a position where a detection beam from
multipoint AF system (90a, 90b) is irradiated on measurement plate
30 previously described in the Y-axis direction.
(a) In this state, main controller 20 performs the former
processing of focus calibration as in the following description.
More specifically, while detecting surface position information of
the end portions on one side and the other side of wafer table WTB
in the X-axis direction that is detected by Z heads 72a, 72b, 72c
and 72d previously described which are in the vicinity of the
respective detection points located at both end sections of the
detection area of the multipoint AF system (90a, 90b), main
controller 20 uses the surface position information as a reference,
and detects surface position information of the measurement plate
30 (refer to FIG. 3) surface previously described using the
multipoint AF system (90a, 90b). Thus, a relation between the
measurement values of Z heads 72a, 72b, 72c and 72d (surface
position information at end portions on one side and the other side
of wafer table WTB in the X-axis direction) and the detection
results (surface position information) at a detection point (the
detection point located in the center or the vicinity thereof out
of a plurality of detection points) on the measurement plate 30
surface of the multipoint AF system (90a, 90b), in a state where
the centerline of wafer table WTB coincides with reference line LV,
is obtained. (b) Next, main controller 20 moves wafer stage WST in
the +Y direction by a predetermined distance, and stops wafer stage
WST at a position where measurement plate 30 is located directly
below projection optical system PL. Then, main controller 20
performs the latter processing of focus calibration as follows.
More specifically, as is shown in FIG. 11B, while controlling the
position of measurement plate 30 (wafer stage WST) in the optical
axis direction of projection optical system PL (the Z position),
using surface position information measured by Z heads 72a to 72d
as a reference as in the former processing of focus calibration,
main controller 20 measures an aerial image of a measurement mark
formed on reticle R or on a mark plate (not shown) on reticle stage
RST by a Z direction scanning measurement whose details are
disclosed in, for example, the pamphlet of International
Publication No. 2005/124834 and the like, using aerial image
measurement device 45, and based on the measurement results,
measures the best focus position of projection optical system PL.
During the Z direction scanning measurement described above, main
controller 20 takes in measurement values of a pair of Z heads 743
and 763 which measure the surface position information at end
portions on one side and the other side of wafer table WTB in the
X-axis direction, in synchronization with taking in output signals
from aerial image measurement device 45. Then, main controller 20
stores the values of Z heads 74.sub.3 and 76.sub.3 corresponding to
the best focus position of projection optical system PL in memory
(not shown). Incidentally, the reason why the position (Z position)
related to the optical axis direction of projection optical system
PL of measurement plate 30 (wafer stage WST) is controlled using
the surface position information measured in the latter processing
of the focus calibration by Z heads 72a to 72d is because the
latter processing of the focus calibration is performed during the
focus mapping previously described.
[0197] In this case, because liquid immersion area 14 is formed
between projection optical system PL and measurement plate 30
(wafer table WTB) as shown in FIG. 11B, the measurement of the
aerial image is performed via projection optical system PL and the
water. Further, although it is omitted in FIG. 11B, because
measurement plate 30 and the like of aerial image measurement
device 45 are installed in wafer stage WST (wafer table WTB), and
the light receiving elements are installed in measurement stage
MST, the measurement of the aerial image described above is
performed while wafer stage WST and measurement stage MST maintain
a contact state (or a proximity state) (refer to FIG. 20).
(c) Accordingly, main controller 20 can obtain the offset at the
representative detection point of the multipoint AF system (90a,
90b), or more specifically, the deviation between the best focus
position of projection optical system PL and the detection origin
of the multipoint AF system, based on the relation between the
measurement values of Z heads 72a to 72d (surface position
information at the end portions on one side and the other side in
the X-axis direction of wafer table WTB) and the detection results
(surface position information) of the measurement plate 30 surface
by the multipoint AF system (90a, 90b) obtained in (a) described
above, in the former processing of focus calibration, and also on
the measurement values of Z heads 74.sub.3 and 76.sub.3 (that is,
surface position information at the end portions on one side and
the other side in the X-axis direction of wafer table WTB)
corresponding to the best focus position of projection optical
system PL obtained in (b) described above, in the latter processing
of focus calibration. In the embodiment, the representative
detection point is, for example, the detection point in the center
of the plurality of detection points or in the vicinity thereof,
but the number and/or the position may be arbitrary. In this case,
main controller 20 adjusts the detection origin of the multipoint
AF system so that the offset at the representative detection point
becomes zero. The adjustment may be performed, for example,
optically, by performing angle adjustment of a plane parallel plate
(not shown) inside photodetection system 90b, or the detection
offset may be electrically adjusted. Alternatively, the offset may
be stored, without performing adjustment of the detection origin.
In this case, adjustment of the detection origin is to be performed
by the optical method referred to above. This completes the focus
calibration of the multipoint AF system (90a, 90b). Incidentally,
because it is difficult to make the offset become zero at all the
remaining detection points other than the representative detection
point by adjusting the detection origin optically, it is desirable
to store the offset after the optical adjustment at the remaining
detection points.
[0198] Next, offset correction of detection values among a
plurality of light-receiving elements (sensors) that individually
correspond to a plurality of detection points of the multiple AF
system (90a, 90b) (hereinafter, referred to as offset correction
among AF sensors) will be described.
[0199] On the offset correction among AF sensors, as is shown in
FIG. 12A, main controller 20 makes irradiation system 90a of the
multipoint AF system (90a, 90b) irradiate detection beams to FD bar
46 equipped with a predetermined reference plane, and takes in
output signals from photodetection system 90b of the multipoint AF
system (90a, 90b) that receives the reflected lights from the FD
bar 46 surface (reference plane).
[0200] In this case, if the FD bar 46 surface is set parallel to
the XY plane, main controller 20 can perform the offset correction
among AF sensors by obtaining a relation among the detection values
(measurement values) of a plurality of sensors that individually
correspond to a plurality of detection points based on the output
signals loaded in the manner described above and storing the
relation in a memory, or by electrically adjusting the detection
offset of each sensor so that the detection values of all the
sensors become, for example, the same value as the detection value
of a sensor that corresponds to the representative detection point
on the focus calibration described above.
[0201] In the embodiment, however, as is shown in FIG. 12A, because
main controller 20 detects the inclination of the surface of
measurement stage MST (integral with FD bar 46) using Z heads
74.sub.4, 74.sub.5, 76.sub.1 and 76.sub.2 when taking in the output
signals from photodetection system 90b of the multipoint AF system
(90a, 90b), the FD bar 46 surface does not necessarily have to be
set parallel to the XY plane. In other words, as is modeled in FIG.
12B, when it is assumed that the detection value at each detection
point is the value as severally indicated by arrows in the drawing,
and the line that connects the upper end of the detection values
has an unevenness as shown in the dotted line in the drawing, each
detection value only has to be adjusted so that the line that
connects the upper end of the detection values becomes the solid
line shown in the drawing.
[0202] Next, a parallel processing operation that uses wafer stage
WST and measurement stage MST in exposure apparatus 100 of the
embodiment will be described based on FIGS. 13 to 23. Incidentally,
during the operation below, main controller 20 performs the
open/close control of each valve of liquid supply unit 5 of local
liquid immersion unit 8 and liquid recovery unit 6 in the manner
previously described, and water is constantly filled on the
outgoing surface side of tip lens 191 of projection optical system
PL. However, in the description below, for the sake of simplicity,
the explanation related to the control of liquid supply unit 5 and
liquid recovery unit 6 will be omitted. Further, many drawings are
used in the operation description hereinafter, however, reference
codes may or may not be given to the same member for each drawing.
More specifically, the reference codes written are different for
each drawing, however, such members have the same configuration,
regardless of the indication of the reference codes. The same can
be said for each drawing used in the description so far.
[0203] FIG. 13 shows a state in which an exposure by the
step-and-scan method of wafer W mounted on wafer stage WST is
performed. This exposure is performed by repeating a movement
between shots in which wafer stage WST is moved to a scanning
starting position (acceleration staring position) to expose each
shot area on wafer W and scanning exposure in which the pattern
formed on reticle R is transferred onto each shot area by the
scanning exposure method, based on results of wafer alignment (e.g.
Enhanced Global Alignment (EGA)) and the like which has been
performed prior to the beginning of exposure. Further, exposure is
performed in the following order, from the shot area located on the
-Y side on wafer W to the shot area located on the +Y side.
Incidentally, exposure is performed in a state where liquid
immersion area 14 is formed in between projection unit PU and wafer
W.
[0204] During the exposure described above, the position (including
rotation in the .theta.z direction) of wafer stage WST (wafer table
WTB) in the XY plane is controlled by main controller 20, based on
measurement results of a total of three encoders which are the two
Y encoders 70A and 70C, and one of the two X encoders 70B and 70D.
In this case, the two X encoders 70B and 70D are made up of two X
heads 66 that face X scale 39X.sub.1 and 39X.sub.2, respectively,
and the two Y encoders 70A and 70C are made up of Y heads 65 and 64
that face Y scales 39Y.sub.1 and 39Y.sub.2, respectively. Further,
the Z position and rotation (rolling) in the .theta.y direction of
wafer stage WST are controlled, based on measurement results of Z
heads 74.sub.i and 76.sub.j, which respectively belong to head
units 62C and 62A facing the end section on one side and the other
side of the surface of wafer table WTB in the X-axis direction,
respectively. The .theta.x rotation (pitching) of wafer stage WST
is controlled based on measurement values of Y interferometer 16.
Incidentally, in the case three or more Z heads including Z head
74.sub.i and 76.sub.i face the surface of the second water
repellent plate 28b of wafer table WTB, it is also possible to
control the position of wafer stage WST in the Z-axis direction,
the .theta.y rotation (rolling), and the .theta.x rotation
(pitching), based on the measurement values of Z heads 74.sub.i,
76.sub.i and the other one head. In any case, the control (more
specifically, the focus leveling control of wafer W) of the
position of wafer stage WST in the Z-axis direction, the rotation
in the .theta.y direction, and the rotation in the .theta.x
direction is performed; based on results of a focus mapping
performed beforehand.
[0205] At the position of wafer stage WST shown in FIG. 13, while X
head 66.sub.5 (shown circled in FIG. 13) faces X scale 39X.sub.1,
there are no X heads 66 that face X scale 39X.sub.2. Therefore,
main controller 20 uses one X encoder 70B and two Y encoders 70A
and 70C so as to perform position (X, Y, .theta.z) control of wafer
stage WST. In this case, when wafer stage WST moves from the
position shown in FIG. 13 to the -Y direction, X head 66.sub.5
moves off of (no longer faces) X scale 39X.sub.1, and X head
66.sub.4 (shown circled in a broken line in FIG. 13) faces X scale
39X.sub.2 instead. Therefore, main controller 20 switches the
control to a position (X, Y, .theta.z) control of wafer stage WST
that uses one X encoder 70D and two Y encoders 70A and 70C.
[0206] Further, when wafer stage WST is located at the position
shown in FIG. 13, Z heads 74.sub.3 and 76.sub.3 (shown circled in
FIG. 13) face Y scales 39Y.sub.2 and 39Y.sub.1, respectively.
Therefore, main controller 20 performs position (Z, .theta.y)
control of wafer stage WST using Z heads 74.sub.3 and 76.sub.3. In
this case, when wafer stage WST moves from the position shown in
FIG. 13 to the +X direction, Z heads 74.sub.3 and 76.sub.3 move off
of (no longer faces) the corresponding Y scales, and Z heads
74.sub.4 and 76.sub.4 (shown circled in a broken line in FIG. 13)
respectively face Y scales 39Y.sub.2 and 39Y.sub.1 instead.
Therefore, main controller 20 switches to position (Z, .theta.y)
control of wafer stage WST using Z heads 74.sub.4 and 76.sub.4.
[0207] In this manner, main controller 20 performs position control
of wafer stage WST by consistently switching the encoder to use
depending on the position coordinate of wafer stage WST.
[0208] Incidentally, independent from the position measurement of
wafer stage WST described above using the measuring instrument
system described above, position (X, Y, Z, .theta.x, .theta.y,
.theta.z) measurement of wafer stage WST using interferometer
system 118 is constantly performed.
[0209] In this case, the X position and .theta.z rotation (yawing)
of wafer stage WST or the X position are measured using X
interferometers 126, 127, or 128, the Y position, the .theta.x
rotation, and the .theta.z rotation are measured using Y
interferometer 16, and the Y position, the Z position, the .theta.y
rotation, and the .theta.z rotation are measured using Z
interferometers 43A and 43B (not shown in FIG. 13, refer to FIG. 1
or 2) that constitute interferometer system 118. Of X
interferometers 126, 127, and 128, one interferometer is used
according to the Y position of wafer stage WST. As indicated in
FIG. 13, X interferometer 126 is used during exposure. The
measurement results of interferometer system 118 except for
pitching (.theta.x rotation) are used for position control of wafer
stage WST secondarily, or in the case of backup which will be
described later on, or when measurement using encoder system 150
cannot be performed.
[0210] When exposure of wafer W has been completed, main controller
20 drives wafer stage WST toward unloading position UP. On this
drive, wafer stage WST and measurement stage MST which were apart
during exposure come into contact or move close to each other with
a clearance of around 300 .mu.m in between, and shift to a scrum
state. In this case, the -Y side surface of FD bar 46 on
measurement table MTB and the +Y side surface of wafer table WTB
come into contact or move close together. And by moving both stages
WST and MST in the -Y direction while maintaining the scrum
condition, liquid immersion area 14 formed under projection unit PU
moves to an area above measurement stage MST. For example, FIGS. 14
and 15 show the state after the movement.
[0211] When wafer stage WST moves further to the -Y direction and
moves off from the effective stroke area (the area in which wafer
stage WST moves at the time of exposure and wafer alignment) after
the drive of wafer stage WST toward unloading position UP has been
started, all the X heads and Y heads, and all the Z heads that
constitute encoder 70A to 70D move off from the corresponding scale
on wafer table WTB. Therefore, position control of wafer stage WST
based on the measurement results of encoders 70A to 70D and the Z
heads is no longer possible. Just before this, main controller 20
switches the control to a position control of wafer stage WST based
on the measurement results of interferometer system 118. In this
case, of the three X interferometers 126, 127, and 128, X
interferometer 128 is used.
[0212] Then, wafer stage WST releases the scrum state with
measurement stage MST, and then moves to unloading position UP as
shown in FIG. 14. After the movement, main controller 20 unloads
wafer W on wafer table WTB. And then, main controller 20 drives
wafer stage WST in the +X direction to loading position LP, and the
next wafer W is loaded on wafer table WTB as shown in FIG. 15.
[0213] In parallel with these operations, main controller 20
performs Sec-BCHK (a secondary base line check) in which position
adjustment of FD bar 46 supported by measurement stage MST in the
XY plane and baseline measurement of the four secondary alignment
system AL2.sub.1 to AL2.sub.4 are performed. Sec-BCHK is performed
on an interval basis for every wafer exchange. In this case, in
order to measure the position (the .theta.z rotation) in the XY
plane, Y encoders 70E.sub.2 and 70F.sub.2 previously described are
used.
[0214] Next, as shown in FIG. 16, main controller 20 drives wafer
stage WST and positions reference mark FM on measurement plate 30
within a detection field of primary alignment system AL1, and
performs the former process of Pri-BCHK (a primary baseline cheek)
in which the reference position is decided for baseline measurement
of alignment system AL1, and AL2.sub.1 to AL2.sub.4.
[0215] On this process, as shown in FIG. 16, two Y heads 68.sub.2
and 67.sub.3 and one X head 66.sub.1 (shown circled in the drawing)
come to face Y scales 39Y.sub.1 and 39Y.sub.2, and X scale
39X.sub.2, respectively. Then, main controller 20 switches the
stage control from a control using interferometer system 118, to a
control using encoder system 150 (encoders 70F.sub.1, 70E.sub.1,
and 70D). Interferometer system 118 is used secondarily again,
except in measurement of the .theta.x rotation. Incidentally, of
the three X interferometers 126, 127, and 128, X interferometer 127
is used.
[0216] Next, while controlling the position of wafer stage WST
based on the measurement values of the three encoders described
above, main controller 20 begins the movement of wafer stage WST in
the +Y direction toward a position where an alignment mark arranged
in three first alignment shot areas is detected.
[0217] Then, when wafer stage WST reaches the position shown in
FIG. 17, main controller 20 stops wafer stage WST. Prior to this
operation, main controller 20 activates (turns ON) Z heads 72a to
72d and starts measurement of the Z-position and the tilt (the
.theta.y rotation and the .theta.x rotation) of wafer table WTB at
the point in time when all of or part of Z heads 72a to 72d face(s)
wafer table WTB, or before that point in time.
[0218] After wafer stage WST is stopped, main controller 20 detects
the three alignment marks arranged in the first alignment shot area
substantially at the same time and also individually (refer to the
star-shaped marks in FIG. 17), using primary alignment system AL1,
and secondary alignment systems AL2.sub.2 and AL2.sub.3, and makes
a link between the detection results of the three alignment systems
AL1, AL2.sub.2, and AL2.sub.3 and the measurement values of the
three encoders above at the time of the detection, and stores them
in memory (not shown).
[0219] As in the description above, in the embodiment, the shift to
the contact state (or proximity state) between measurement stage
MST and wafer stage WST is completed at the position where
detection of the alignment marks of the first alignment shot area
is performed. And from this position, main controller 20 begins to
move both stages WST and MST in the +Y direction (step movement
toward the position for detecting the five alignment marks arranged
in the second alignment shot area) in the contact state (or
proximity state). Prior to starting the movement of both stages WST
and MST in the +Y direction, as shown in FIG. 17, main controller
20 begins irradiation of a detection beam from irradiation system
90 of the multipoint AF system (90a, 90b) to wafer table WTB.
Accordingly, a detection area of the multipoint AF system is formed
on wafer table WTB.
[0220] Then, when both stages WST and MST reach the position shown
in FIG. 18 during the movement of both stages WST and MST in the +Y
direction, main controller 20 performs the former process of the
focus calibration, and obtains the relation between the measurement
values (surface position information on one side and the other side
of wafer table WTB in the X-axis direction) of Z heads 72a, 72b,
72c, and 72d, in a state where the center line of wafer table WTB
coincides with reference axis LV, and the detection results
(surface position information) of the surface of measurement plate
30 by the multipoint AF system (90a, 90b). At this point, liquid
immersion area 14 is formed on the upper surface of FD bar 46.
[0221] Then, both stages WST and MST move further in the +Y
direction while maintaining the contact state (or proximity state),
and reach the position shown in FIG. 19.
[0222] Then, main controller 20 detects the alignment mark arranged
in the five second alignment shot areas substantially at the same
time as well as individually (refer to the star-shaped marks in
FIG. 19), using the five alignment systems AL1, and AL2.sub.1 to
AL2.sub.4, and makes a link between the detection results of the
five alignment systems AL1, and AL2.sub.1 to AL2.sub.4 and the
measurement values of the three encoders measuring the position of
wafer stage WST in the XY plane at the time of the detection, and
then stores them in memory (not shown) (or in memory 34). At this
point, main controller 20 controls the position within the XY plane
of wafer stage WST based on the measurement values of X head
66.sub.2 (X linear encoder 70D) that faces X scale 39X.sub.2 and Y
linear encoders 70A and 70C.
[0223] Further, after the simultaneous detection of the alignment
marks arranged in the five second alignment shot areas ends, main
controller 20 starts again movement in the +Y direction of both
stages WST and MST in the contact state (or proximity state), and
at the same time, starts the focus mapping previously described
using Z heads 72a to 72d and the multipoint AF system (90a, 90b),
as is shown in FIG. 19.
[0224] Then, when both stages WST and MST reach the position shown
in FIG. 20 where measurement plate 30 is located directly below
projection optical system PL, main controller 20 performs the
latter processing of focus calibration in a state continuing the
control of Z position of wafer stage WST (measurement plate 30)
that uses the surface position information measured by Z heads 72a
to 72d as a reference, without switching the Z head used for
position (Z position) control of wafer stage WST in the optical
axis direction of projection optical system PL to Z heads 74.sub.i
and 76.sub.j.
[0225] Then, main controller 20 obtains the offset at the
representative detection point of the multipoint AF system (90a,
90b) based on the results of the former processing and latter
processing of focus calibration described above, and stores the
offset in the internal memory. And, on reading mapping information
obtained from the results of focus mapping at the time of exposure,
main controller 20 is to add the offset to the mapping
information.
[0226] Incidentally, in the state of FIG. 20, the focus mapping is
being continued.
[0227] When wafer stage WST reaches the position shown in FIG. 21
by both stages WST in the contact state (or, proximity state), the
movement of the +Y direction of MST, main controller 20 stops wafer
stage WST at the position, and it makes just continue the movement
to the +Y direction about measurement stage MST. Then, main
controller 20 detects the alignment mark arranged in the five
second alignment shot areas substantially at the same time as well
as individually (refer to the star-shaped marks in FIG. 21), using
the five alignment systems AL1, and AL2.sub.1 to AL2.sub.4, and
makes a link between the detection results of the five alignment
systems AL1, and AL2.sub.1 to AL2.sub.4 and the measurement values
of the three encoders at the time of the detection, and then stores
them in the memory (not shown). Also at this point in time, the
focus mapping is being continued.
[0228] Meanwhile, after a predetermined period of time from the
suspension of wafer stage WST described above, measurement stage
MST and wafer stage WST move from the contact state (or proximity
state) into a separation state. After moving into the separation
state, main controller 20 stops the movement of measurement stage
MST when measurement stage MST reaches an exposure start waiting
position where measurement stage MST waits until exposure is
started.
[0229] Next, main controller 20 starts the movement of wafer stage
WST in the +Y direction toward a position where the alignment mark
arranged in the three fourth alignment shots are detected. At this
point in time, the focus mapping is being continued. Meanwhile,
measurement stage MST is waiting at the exposure start waiting
position described above.
[0230] Then, when wafer stage WST reaches the position shown in
FIG. 22, main controller 20 immediately stops wafer stage WST, and
almost simultaneously and individually detects the alignment marks
arranged in the three fourth alignment shot areas on wafer W (refer
to star-shaped marks in FIG. 22) using primary alignment system AL1
and secondary alignment systems AL2.sub.2 and AL2.sub.3, links the
detection results of three alignment systems AL1, AL2.sub.2 and
AL2.sub.3 and the measurement values of the three encoders out of
the four encoders above at the time of the detection, and stores
them in memory (not shown). Also at this point in time, the focus
mapping is being continued, and measurement stage MST is still
waiting at the exposure start waiting position. Then, using the
detection results of a total of 16 alignment marks and the
measurement values of the corresponding encoders obtained in the
manner described above, main controller 20 computes array
information (coordinate values) of all the shot areas on wafer W on
an alignment coordinate system (an XY coordinate system whose
origin is placed at the detection center of primary alignment
system AL1) that is set by the measurement axes of encoders 70B,
70D, 70E.sub.1, and 70F.sub.1 of encoder system 150, by performing
a statistical computation disclosed in, for example, Kokai
(Japanese Patent Unexamined Application Publication) No. 61-44429
(and the corresponding U.S. Pat. No. 4,780,617) and the like.
[0231] Next, main controller 20 continues the focus mapping while
moving wafer stage WST in the +Y direction again. Then, when the
detection beam from the multipoint AF system (90a, 90b) begins to
miss the wafer W surface, as is shown in FIG. 23, main controller
20 ends the focus mapping.
[0232] After the focus mapping has been completed, main controller
20 moves wafer table WTB (wafer stage WST) to a scanning starting
position (exposure starting position) for exposure of the first
shot on wafer W, and during the movement, main controller 20
switches the Z heads used for control of the Z position and the
.theta.y rotation of wafer stage WST from Z heads 72a to 72d to Z
heads 74.sub.i and 74.sub.j while maintaining the Z position, the
.theta.y rotation, and the .theta.x rotation of wafer stage WST.
After this switching, based on the results of the wafer alignment
(EGA) previously described and the latest baselines and the like of
the five alignment systems AL1 and AL2.sub.1 to AL2.sub.4, main
controller 20 performs exposure by a step-and-scan method in a
liquid immersion exposure, and sequentially transfers a reticle
pattern to a plurality of shot areas on wafer W. Hereinafter, a
similar operation is executed repeatedly.
[0233] Next, a computation method of the Z position and the amount
of tilt of wafer stage WST using the measurement results of the Z
heads will be described. Main controller 20 uses the four Z heads
70a to 70d that constitute surface position measurement system 180
(refer to FIG. 6) at the time of focus calibration and focus
mapping, and measures height Z and tilt (rolling) .theta.y of wafer
table WTB. Further, main controller 20 uses two Z heads 74.sub.i
and 76.sub.j (i and j are one of 1 to 5) at the time of exposure,
and measures height Z and tilt (rolling) .theta.y of wafer table
WTB. Incidentally, each Z head irradiates a probe beam on the upper
surface (a surface of a reflection grating formed on the upper
surface) of the corresponding Y scales 39Y.sub.1 or 39Y.sub.2, and
measures the surface position of each scale (reflection grating) by
receiving the reflected light.
[0234] FIG. 24A shows a two-dimensional plane having height ZO,
rotation angle (an angle of inclination) around the X-axis
.theta.x, and rotation angle (an angle of inclination) around the
Y-axis .theta.y at a reference point O. Height Z at position (X, Y)
of this plane is given by a function according to the next formula
(8).
f(X,Y)=-tan .theta.yX+tan .theta.xY+Z.sub.0 (8)
[0235] As shown in FIG. 24B, at the time of the exposure, height Z
from a movement reference surface (a surface that is substantially
parallel to the XY plane) of wafer table WTB and rolling .theta.y
are measured at an intersection point (reference point) O of a
movement reference surface of wafer table WTB and optical axis AX
of projection optical system PL, using two Z heads 74.sub.i and
76.sub.i (i and j are one of 1 to 5). In this case, Z heads
74.sub.3 and 76.sub.3 are used as an example. Similar to the
example shown in FIG. 24A, the height of wafer table WTB at
reference point O will be expressed as Z.sub.0, the tilt (pitching)
around the X-axis will be expressed as .theta.x, and the tilt
(rolling) around the Y-axis will be expressed as .theta.y. In this
case, measurement values Z.sub.L and Z.sub.R of the surface
position of (reflection gratings formed on) Y scales 39Y.sub.1 and
39Y.sub.2 indicated by Z head 74.sub.3, which is located at
coordinate (p.sub.L, q.sub.L), and Z head 76.sub.3, which is
located at coordinate (p.sub.R, q.sub.R), in the XY plane,
respectively, follow theoretical formulas (9) and (10), similar to
formula (8).
Z.sub.L=-tan .theta.yp.sub.L+tan .theta.xq.sub.L+Z.sub.0 (9)
Z.sub.R=-tan .theta.yp.sub.R+tan .theta.xq.sub.R+Z.sub.0 (10)
[0236] Accordingly, from theoretical formulas (9) and (10), height
Z.sub.0 and rolling .theta.y of wafer table WTB at reference point
O can be expressed as in the following formulas (11) and (12),
using measurement values Z.sub.L and Z.sub.R of Z heads 74.sub.3
and 76.sub.3.
Z.sub.0={Z.sub.L+Z.sub.R-tan .theta.x(q.sub.L+q.sub.R)}/2 (11)
tan .theta.y={Z.sub.L-Z.sub.R-tan
.theta.x(q.sub.L-q.sub.R)}/(p.sub.R-p.sub.L) (12)
[0237] Incidentally, in the case of using other combinations of Z
heads as well, by using theoretical formulas (11) and (12), height
Z.sub.0 and rolling .theta.y of wafer table WTB at reference point
O can be computed. However, pitching .theta.x uses the measurement
results of another sensor system (in the embodiment, interferometer
system 118).
[0238] As shown in FIG. 24B, at the time of focus calibration and
focus mapping, height Z of wafer table WTB and rolling .theta.y at
a center point O' of a plurality of detection points of the
multipoint AF system (90a, 90b) are measured, using four Z heads
72a to 72d. Z heads 72a to 72d, in this case, are respectively
placed at position (X, Y)=(p.sub.a, q.sub.a), (p.sub.b, q.sub.b),
(p.sub.c, q.sub.c), (p.sub.a, q.sub.d). As shown in FIG. 24B, these
positions are set symmetric to center point O'=(Ox', Oy'), or more
specifically, p.sub.a=p.sub.b, p.sub.c=p.sub.d, q.sub.a=q.sub.c,
q.sub.b=q.sup.d, and also
(p.sub.a+p.sub.c)/2=(p.sub.b+p.sub.a)/2=Ox',
(q.sub.a+q.sub.b)/2=(q.sub.c+q.sub.a)/2=Oy'.
[0239] From average (Za+Zb)/2 of measurement values Za and Zb of Z
head 72a and 72b, height Ze of wafer table WTB at a point e of
position (p.sub.a=p.sub.b, Oy') can be obtained, and from average
(Zc+Zd)/2 of the measurement values Zc and Zd of Z heads 70c and
70d, height Zf of wafer table WTB at a point f of position
(p.sub.c=p.sub.d, Oy') can be obtained. In this case, when the
height of wafer table WTB at center point O' is expressed as
Z.sub.0, and the tilt (rolling) around the Y-axis is expressed as
.theta.y, then, Ze and Zf follow theoretical formulas (13) and
(14), respectively.
Ze{=(Za+Zb)/2}=-tan .theta.y(p.sub.a+p.sub.b-2Ox')/2+Z.sub.0
(13)
Zf{=(Zc+Zd)/2}=-tan .theta.y(p.sub.c+p.sub.d-2Ox')/2+Z.sub.0
(14)
[0240] Accordingly, from theoretical formulas (13) and (14), height
Z.sub.0 of wafer table WTB and rolling .theta.y at center point O'
can be expressed as in the following formulas (15) and (16), using
measurement values Za to Zd of Z heads 70a to 70d.
Z.sub.0=(Ze+Zf)/2=(Za+Zb+Zc+Zd)/4 (15)
tan .theta. y = - 2 ( Ze - Zf ) / ( p a + p b - p c - p d ) = - (
Za + Zb - Zc - Zd ) / ( p a + p b - p c - p d ) ( 16 )
##EQU00001##
[0241] However, pitching .theta.x uses the measurement results of
another sensor system (in the embodiment, interferometer system
118).
[0242] As shown in FIG. 16, immediately after switching from servo
control of wafer stage WST by interferometer system 118 to servo
control by encoder system 150 (encoders 70A to 70F) and surface
position measurement system 180 (Z head systems 72a to 72d,
74.sub.1 to 74.sub.5, and 76.sub.1 to 76.sub.5), because only two
heads, Z heads 72b and 72d, face the corresponding Y scales
39Y.sub.1 and 39Y.sub.2, the Z and .theta.y positions of wafer
table WTB at center point O' cannot be computed using formulas (15)
and (16). In such a case, the following formulas (17) and (18) are
applied.
Z.sub.0={Zb+Zd-tan .theta.x(q.sub.b+q.sub.d-2.theta.y)}/2 (17)
tan .theta.y={Zb-Zd-tan
.theta.x(q.sub.b-q.sub.d)}/(p.sub.a-p.sub.b) (18)
[0243] Then, when wafer stage WST has moved in the +Z direction,
and accompanying this move, after Z heads 72a and 72c have faced
the corresponding Y scales 39Y.sub.1 and 39Y.sub.2, formulas (15)
and (16) above are applied.
[0244] As previously described, scanning exposure to wafer W is
performed, after finely driving wafer stage WST in the Z-axis
direction and tilt direction according to the unevenness of the
surface of wafer W, and having adjusted the surface position of
wafer W and the tilt (focus leveling) so that the exposure area IA
portion on the surface of wafer W matches within the range of the
depth of focus of the image plane of projection optical system PL.
Therefore, prior to the scanning exposure, focus mapping to measure
the unevenness (a focus map) of the surface of wafer W is
performed. In this case, as shown in FIG. 10B, the unevenness of
the surface of wafer W is measured at a predetermined sampling
interval (in other words, a Y interval) while moving wafer stage
WST in the +Y direction, using the multipoint AF system (90a, 90b)
with the surface position of wafer table WTB (or to be more
precise, the corresponding Y scales 39Y.sub.1 and 39Y.sub.2)
measured using Z heads 72a to 72d serving as a reference.
[0245] To be specific, as shown in FIG. 248, surface position Ze of
wafer table WTB at point e can be obtained from the average of
surface positions Za and Zb of Y scale 39Y.sub.2, which is measured
using Z heads 72a and 72b, and surface position Zf of wafer table
WTB at point if can be obtained from the average of surface
positions Zc and Zd of Y scale 39Y.sub.1, which is measured using Z
heads 72c and 72d. In this case, the plurality of detection points
of the multipoint AF system and center O' of these points are
located on a straight line of parallel to the X-axis and connecting
point e and point f. Therefore, as shown in FIG. 10C, by using a
straight line expressed in the following formula (19) connecting
surface position Ze at point e (P1 in FIG. 10C) of wafer table WTB
and surface position Zf at point f (P2 in FIG. 10C) as a reference,
surface position Z.sub.Ok of the surface of wafer W at detection
point X.sub.k is measured, using the multipoint AF system (90a,
90b).
Z(X)=-tan .theta.yX+Z.sub.0 (19)
[0246] However, Z.sub.0 and tan .theta.y can be obtained from
formulas (17) and (18) above, using measurement results Za to Zd of
Z heads 72a to 72d. From the results of surface position Z.sub.Ok
that has been obtained, unevenness data (focus map) Z.sub.k of the
surface of wafer W can be obtained as in the following formula
(20).
Z.sub.k=Z.sub.0k-Z(X.sub.k) (20)
[0247] At the time of exposure, by finely driving wafer stage WST
in the Z-axis direction and the tilt direction according to focus
map Z.sub.k obtained in the manner described above, focus is
adjusted, as is previously described. At the time of the exposure
here, the surface position of wafer table WTB (or to be more
precise, the corresponding Y scales 39Y.sub.2 and 39Y.sub.1) is
measured, using Z heads 74.sub.i and 76.sub.j (i, j=1-5).
Therefore, reference line Z(X) of focus map Z.sub.k is set again.
However, Z.sub.0 and tan .theta.y can be obtained from formulas
(11) and (12) above, using the measurement results Z.sub.L and
Z.sub.R of Z heads 74.sub.i and 76.sub.j (i, j=1-5). From the
procedure described so far, the surface position of the surface of
wafer W is converted to Z.sub.k+Z(X.sub.k).
[0248] In exposure apparatus 100 of the embodiment, as shown in
FIGS. 25A and 25B, in the effective stroke range (a range where the
stage moves for alignment, exposure operation, and focus mapping)
of wafer stage WST, the Z heads are placed so that at least one of
Z heads 76.sub.j and 74.sub.i (j and i are one of 1 to 5) or one of
72a to 72d faces each of the Y scales 39Y.sub.1 and 39Y.sub.2,
without fail. In FIGS. 25A and 25B, the Z head which faces the
corresponding Y scale is shown surrounded in a circle.
[0249] In this case, when wafer stage WST is to be driven in a
direction indicated by an outlined arrow (the +X direction) as
shown in FIG. 25A, as indicated by arrow f.sub.1, the Z head which
faces Y scale 39Y.sub.2 is switched from Z head 74.sub.3 shown
circled by a solid line to a Z head 74.sub.4 which is shown circled
by a dotted line. Further, when wafer stage WST is to be driven
furthermore in a direction indicated by an outlined arrow (the +X
direction) as shown in FIG. 25B, as indicated by arrow f.sub.2, the
Z head which faces Y scale 39Y.sub.1 is switched from Z head
76.sub.3 shown circled by a solid line to a Z head 76.sub.4 which
is shown circled by a dotted line. In this manner, Z heads 74.sub.i
and 76.sub.j (i, j=1-5) are sequentially changed to the next head,
with the movement of wafer stage WST in the X-axis direction.
Incidentally, at the time of switching of the Z head, a return
processing in which setting of the reference surface position (the
origin) and measurement preparation are performed, or furthermore,
a linkage process to keep the continuity of the measurement
results, is performed. Details on these processes will be described
later in the description.
[0250] Next, a switching procedure of the Z head will be described,
based on FIGS. 26A to 26E and also appropriately using other
drawings as a reference, taking the switching from Z head 76.sub.3
to 76.sub.4 shown in arrow f.sub.2 in FIG. 25B as an example. In
FIG. 26A, a state before the switching is shown. In this state, Z
head 76.sub.3 facing the scanning area (the area where the
diffraction grating is arranged) on Y scale 39Y.sub.1 is operating,
and Z head 76.sub.4 which has moved away from the scanning area is
suspended. Here, the operating (focus servo) Z heads are shown in a
black circle, and the suspended or waiting (scale servo) Z heads
are shown in an outlined circle, respectively. Based on measurement
values of the operating Z head 76.sub.3, main controller 20
computes the position of wafer stage WST. In this case, the Z head
used for computing the position of wafer stage WST is shown
surrounded by a double circle.
[0251] When wafer stage WST moves in the +X direction from the
state shown in FIG. 26A, Y scale 39Y.sub.1 is displaced in the +X
direction, and Z head 76.sub.4 which is suspended approaches the
scanning area on Y scale 39Y.sub.1. Then, main controller 20
confirms that Z head 76.sub.4 has come within a predetermined
distance from the scanning area, and performs the return processing
of Z head 76.sub.4.
[0252] Now, the return processing of Z head 76.sub.4 will be
described, referring to FIGS. 27A to 27C. As shown in FIG. 27A,
reference surface position (origin) S.sub.0 of Z head 76.sub.4 is
to be set at the time of initial operation of the Z head, such as
during the start up of exposure apparatus 100 as is previously
described.
[0253] Main controller 20 estimates a predicted value (more
specifically, a predicted surface position S of Y scale 39Y.sub.1)
of the measurement value of Z head 76.sub.4, which is to be
restored from function f(X, Y) of the formula (8) previously
described, using the position of wafer stage WST in directions of
three degree of freedom (Z, .theta.y, .theta.x) obtained from the
measurement results of the operating Z head and interferometer
system 118. Now, into X and Y, the X and Y positions of Z head 764
are substituted. And, as shown in FIG. 27B, main controller 20
displaces Z sensor main section ZH via the drive section (not
shown) in Z head 76.sub.4 so that the measurement value of Z head
76.sub.4 matches the predicted value (Z head 76.sub.4 outputs the
predicted value as a measurement value), and makes the measurement
value coincide with predicted surface position S of probe beam
LB.
[0254] In the state where the returning process described above has
been completed, the focal position of probe beam LB coincides with
predicted surface position S of Y scale 39Y.sub.1. Incidentally,
with the movement of wafer stage WST in directions of three degree
of freedom (Z, .theta.y, .theta.x), predicted surface position S of
Y scale 39Y.sub.1 is also displaced. And, following the
displacement, sensor main section ZH of Z head 76.sub.4 also
performs Z displacement. More specifically, Z head 76.sub.4
performs a follow-up servo (scale servo) with respect to predicted
surface position S of Y scale 39Y.sub.2. Z head 76.sub.4 is waiting
in such a state.
[0255] In this case, in the embodiment, as is previously described,
the distance in the X-axis direction between the two adjacent Z
heads 74.sub.3 and 76.sub.i is set smaller than the effective width
(width of the scanning area) of Y scales 39Y.sub.2 and 39Y.sub.1 in
the X-axis direction. Therefore, a state occurs when Z heads
76.sub.3 and 76.sub.4 simultaneously face the scanning area of Y
scale 39Y.sub.1 as shown in FIG. 26B. Therefore, after main
controller 20 confirms that Z head 76.sub.4 in a waiting (a scale
servo) state has faced the scanning area along with the operating Z
head 76.sub.3 as shown in FIG. 26B, main controller 20 begins focus
servo with respect to the actual surface position of Y scale
39Y.sub.1 of Z head 76.sub.4, as shown in FIG. 27C.
[0256] However, in the waiting (during scale servo to the predicted
surface position) state, focus error (hereinafter simply referred
to as an output, as appropriate) I which is the output of focus
sensor FS is monitored. If output I becomes zero, it can be judged
that the predicted surface position (more specifically, the Z
position of the focus of the probe beam of the Z head) of Y scale
39Y.sub.1 matches the actual surface position. Therefore, main
controller 20 begins the focus servo, after confirming that Z heads
76.sub.3 and 76.sub.4 have faced the scanning area of Y scale
39Y.sub.1, and at the same time, that output I of focus sensor FS
has become zero or approximately 0 (a value which is equal to or
less than a predetermined value, and can be substantially regarded
as zero) as described above. By performing the processing of such a
procedure, the Z head can be shifted smoothly from scale servo to
focus servo. However, at this point in time, while the measurement
value of Z head 76.sub.4 is monitored, it is not used in position
computation (position control) of wafer table WTB (wafer stage
WST).
[0257] Next, as shown in FIG. 26C, while Z head 76.sub.3 which is
to be suspended later faces the scanning area, main controller 20
switches the Z head used to compute the position of wafer stage WST
in directions of two degrees of freedom (Z, .theta.y) from Z head
76.sub.3 to 76.sub.4. However, in this processing, the position of
wafer stage WST in directions of two degrees of freedom (Z,
.theta.y) computed before and after the switching generally becomes
discontinuous. Therefore, a linkage process of the measurement
values which will be described later is performed, as necessary.
After the linkage process has been completed, the Z head to be used
is switched from Z head 76.sub.3 to 76.sub.4. After the switching
has been completed, as shown in FIG. 26D, main controller 20 makes
Z head 76.sub.3 move into a waiting (scale servo) state before
moving off of the scanning area, and then, suspends the operation
when Z head 76.sub.3 is sufficiently distanced from the scanning
area. With the operation described above, the switching of the Z
head is completed, and hereinafter, as shown in FIG. 26E, Z head
76.sub.4 is used.
[0258] In the embodiment, the spacing between adjacent Z heads
74.sub.i (i=1-5), for example, is 70 mm (with some exceptions), and
is set smaller than the effective width of the scanning area of Y
scale 39Y.sub.2 in the X-axis direction, which is, for example, 76
mm. Further, similarly, the spacing between adjacent Z heads
76.sub.j (j=1-5), is 70 mm (with some exceptions), and is set
smaller than the effective width of the scanning area of Y scale
39Y.sub.1 in the X-axis direction, which is, 76 mm. Because of
this, the switching of Z heads 74.sub.i and 76.sub.j (i, j=1-5) can
be carried out smoothly as described above.
[0259] Incidentally, the range in which the two adjacent Z heads
face the scale, or more specifically, the moving distance of wafer
stage WST (wafer table WTB) from a state shown in FIG. 268 to a
state shown in FIG. 26D, for example, is 6 mm. And at the center,
or more specifically, when wafer stage WST is located at the
position shown in FIG. 26C, the Z head that monitors the
measurement values is switched. This switching operation is
completed by the time the Z head which is to be suspended moves off
the scanning area, or more specifically, while wafer stage WST
moves in an area by a distance of 3 mm during the state shown in
FIG. 26C until the state shown in FIG. 26D. Incidentally, in the
case the movement speed of the stage is 1 m/sec, then the switching
operation of the Z head is to be completed within 3 msec.
[0260] Next, the linkage process at the time of switching of the Z
heads 72a to 72d, 74.sub.1 to 74.sub.5, and 76.sub.1 to 76.sub.5,
or more specifically, the reset of the measurement values to
maintain the continuity of the position of wafer stage WST in
directions of two degrees of freedom (Z, .theta.y) computed by the
measurement results of the Z heads will be described, focusing
mainly on the operation of main controller 20.
[0261] In the embodiment, as is previously described, in the
movement stroke range of wafer stage WST at the time of exposure,
at least two Z heads ZsL (one of 74.sub.3, to 74.sub.5) and ZsR
(one of 76.sub.1 to 76.sub.5) constantly observe the movement of
wafer stage WST. Accordingly, when the switching process of the Z
head is performed, three Z heads, to which a third Z head ZsR' is
added to the two Z heads ZsL and ZsR, will be made to observe wafer
stage WST as shown in FIG. 28A. In this case, Z heads ZsL, ZsR, and
ZsR' are located above Y scales 39Y.sub.2, 39Y.sub.1, and
39Y.sub.1, respectively, and are performing the follow-up servo
(focus servo) of the surface position.
[0262] In the embodiment, as shown in FIG. 28A, main controller 20
switches from position (Z, .theta.y) measurement of wafer stage WST
by the two Z heads ZsL and ZsR to position (Z, .theta.y)
measurement of wafer stage WST by the two Z heads ZsL and ZsR'. On
this switching, first of all, main controller 20 substitutes
measurement values Z.sub.L and Z.sub.R of Z heads ZsL and ZsR, to
which offset cancellation (to be described later) have been
performed, into formulas (11) and (12), and computes Z.sub.0 and
.theta.y positions of wafer stage WST at reference point O (an
intersecting point of the movement reference surface of wafer stage
WST and optical axis AX of projection optical system PL) Next,
using the Z.sub.0 and .theta.y positions computed here, and the
.theta.x position measured by interferometer system 118, a
predicted value Z.sub.R' of the third Z head ZsR' is obtained
according to theoretical formula (10). Now, the X position
(p.sub.R') and Y position (q.sub.R') of Z head ZsR' are substituted
into p.sub.R and q.sub.R. And offset O.sub.R'=Z.sub.R'-Z.sub.R0' is
set. In this case, Z.sub.RO' is the actual measurement value of Z
head ZsR', that is, the actual measurement result of the surface
position of the opposing Y scale 39Y.sub.1. Measurement value
Z.sub.R' of Z head ZsR' is given by performing offset correction
using offset O.sub.R' on the actual measurement value Z.sub.R0',
namely by the following formula (21).
Z.sub.R'=Z.sub.R0'+O.sub.R' (21)
[0263] By the treatment using offset O.sub.R', predicted value
Z.sub.R' is set as measurement value Z.sub.R' of Z head ZsR'.
[0264] By the linkage process described above, the switching
operation of the Z head is completed while having maintained the
position (Z.sub.0, .theta.y) of wafer stage WST. From then onward,
from formulas (11) and (12), position coordinate (Z.sub.0,
.theta.y) of wafer stage WST is computed, using measurement values
Z.sub.L and Z.sub.R' of Z heads ZsL and ZsR' which are used after
the switching. However, in formula (11) and formula (12), Z.sub.R',
p.sub.R', q.sub.R' are substituted into Z.sub.R, p.sub.R,
q.sub.R.
[0265] Further, as shown in FIG. 28B, even when main controller 20
switches from position (Z, .theta.y) measurement of wafer stage WST
by the two Z heads ZsL and ZsR to position (Z, .theta.y)
measurement by the two Z heads ZsL' and ZsR, by a procedure similar
to the one previously described, measurement values Z.sub.L and
Z.sub.R of Z heads ZsL and ZsR are substituted into formulas (11)
and (12), and the Z.sub.0 and .theta.y positions of wafer stage WST
at reference point O (the intersecting point of the movement
reference surface of wafer stage WST and optical axis AX of
projection optical system PL) are computed. Next, using Z.sub.0 and
.theta.y computed here, and .theta.x computed by the measurement
results of interferometer system 118, a predicted value Z.sub.L' of
the third Z head ZsL' is obtained according to theoretical formula
(9). Now, the X position (p.sub.L') and Y position (q.sub.L') of Z
head ZsL' are substituted into p.sub.L and q.sub.L. And offset
O.sub.L'=Z.sub.L'-Z.sub.L0' is set. In this case, Z.sub.L0' is the
actual measurement value of Z head ZsL', that is, the actual
measurement result of the surface position of the opposing Y scale
39Y.sub.2. Measurement value Z.sub.L' of Z head ZsL' is given by
performing offset correction using offset O.sub.L' on the actual
measurement value Z.sub.L0', namely by the following formula
(22).
Z.sub.L'=Z.sub.L0'+O.sub.L' (22)
[0266] By the treatment using offset O.sub.L', predicted value
Z.sub.L' is set as measurement value Z.sub.L' of Z head ZsL'.
[0267] By the linkage process described above, the switching
operation of the Z head is completed while having maintained the
position (Z.sub.0, .theta.y) of wafer stage WST. From then onward,
from formulas (11) and (12), position coordinate (Z.sub.0,
.theta.y) of wafer stage WST is computed, using measurement values
Z.sub.L' and Z.sub.R of Z heads ZsL' and ZsR which are used after
the switching. However, in formula (11) and formula (12), Z.sub.L',
p.sub.L', q.sub.L' are substituted into Z.sub.L, p.sub.L,
q.sub.L.
[0268] However, in the actual measurement values (raw measurement
values) of Z head ZsR' or ZsL', various measurement errors are
included. Therefore, main controller 20 shows the value whose error
has been corrected as a measurement value. Accordingly, in the
linkage process described above, main controller 20 uses scale
unevenness error correction information, correction information on
the Z head installation error and the like, and performs an inverse
correction of the theoretical value obtained from formulas (9) and
(10) and computes the raw value before correction, and then sets
the raw value as the measurement value of Z head ZsR' or ZsL'.
Incidentally, it is convenient to include such error correction
information in offset O.sub.R' and O.sub.L' described above, and to
perform error correction simultaneously with the offset correction
(formulas (21) and (22)).
[0269] Incidentally, by applying the coordinate linkage method, the
position (Z, .theta.y) of wafer stage WST which is computed before
and after the switching of the Z heads becomes continuous without
fail. However, an error (a linkage error) may occur, due to the
prediction calculation of the measurement value of the Z head to be
newly used, the offset computation and the like. When exposure of
all the shot areas on the wafer is actually performed, the
switching of the encoder will be performed approximately 100 times.
Accordingly, even if the error which occurs in one linkage process
is small enough to ignore, the errors may be accumulated by
repeating the switching many times, and may come to exceed a
permissible level. Incidentally, assuming that the errors occur at
random, the cumulative error which occurs by performing the
switching 100 times is about 10 times the error which occurs when
the switching is performed once. Accordingly, the precision of the
linkage process must be improved as much as possible, and a stage
control method which is not affected by the linkage accuracy will
have to be employed.
[0270] Therefore, for example, position control of wafer stage WST
is preferably performed using the position coordinate (Z, .theta.y)
of wafer stage WST which has been obtained by applying the
coordinate linkage method, and focus calibration and a focus should
be performed using the position coordinate (Z, .theta.y) of wafer
stage WST which has been obtained from the actual output of the Z
head, without applying the coordinate linkage method. Further, when
the wafer stage WST stops, the offset should be cleared to cancel
out the accumulated linkage error.
[0271] The position coordinate of wafer stage WST is controlled,
for example, at a time interval of 96 .mu.sec. At each control
sampling interval, main controller 20 updates the current position
of wafer stage WST, computes thrust command values and the like to
position the stage to a target position, and outputs the values. As
previously described, the current position of wafer stage WST is
computed from the measurement results of interferometer system 118,
encoder system 150 (encoders 70A to 70F), and surface position
measurement system 180 (Z heads 72a to 72d, 74.sub.1 to 74.sub.5,
and 76.sub.1 to 76.sub.5). Accordingly, main controller 20 monitors
the measurement results of the interferometer, the encoder, and the
Z heads at a time interval (measurement sampling interval) much
shorter than the control sampling interval.
[0272] Therefore, in the embodiment, main controller 20 constantly
continues to receive the measurement values from all the Z heads
(not always two) that face the scanning area (the area where the
probe beams from the Z heads are scanned) of the scales, while
wafer stage WST is within the effective stroke range. And, main
controller 20 performs the switching operation (a linkage operation
between a plurality of Z heads) of the Z heads described above in
synchronization with position control of wafer stage WST which is
performed at each control sampling interval. In such an
arrangement, an electrically high-speed switching operation of the
Z heads will not be required, which also means that costly hardware
to realize such a high-speed switching operation does not
necessarily have to be arranged.
[0273] FIG. 29 conceptually shows the timing of position control of
wafer stage WST, the uptake of the measurement values of the Z
head, and the switching of the Z head in the embodiment. Reference
code CSCK in FIG. 29 indicates the generation timing of a sampling
clock (a control clock) of the position control of wafer stage WST,
and reference code MSCK indicates a generation timing of a sampling
clock (a measurement clock) of the measurement of the Z head (and
interferometer and encoder). Further, reference code CH typically
shows the switching (linkage) of the Z head described in detail in
FIG. 26.
[0274] Main controller 20 executes the switching procedure of the Z
heads by dividing the operation into two stages; the restoration
and the switching process (and the linkage process) of the Z heads.
When describing the switching according to an example shown in FIG.
29, first of all, the Z heads which are operating at the time of
the first control clock are to be of a first combination, ZsL and
ZsR. Main controller 20 monitors the measurement value of these Z
heads, and computes the position coordinate (Z, .theta.y) of wafer
stage WST. Next, according to the position coordinate of wafer
stage WST, main controller 20 obtains all the Z heads which are
above and in the vicinity of the scanning area of the Y scale. And,
from these heads, main controller 20 specifies Z head ZsR' which
needs restoration, and restores the encoder at the time of the
second control clock. In this case, Z head ZsR' which has been
restored is in the waiting state (scale servo state) previously
described, and is switched to the operating state (focus servo
state) after main controller 20 confirms that Z head ZsR' has faced
the scanning area of the Y scale. At this point of time, the
operating Z heads become three, which are, ZsL, ZsR and ZsR'. And
then, main controller 20 specifies the Z head whose measurement
values are to be monitored to compute the position coordinate of
wafer stage WST at the time of the next control clock from the
operating Z heads, according to the position coordinate of wafer
stage WST. Assume that a second combination ZsL and ZsR' are
specified here. Main controller 20 confirms whether this specified
combination matches the combination that was used to compute the
position coordinate of wafer stage WST at the time of the previous
control clock. In this example, Z head ZsR in the first combination
and Z head ZsR' in the second combination are different. Therefore,
main controller 20 performs a linkage process CH to the second
combination at the time of the third control clock. Hereinafter,
main controller 20 monitors the measurement values of the second
combination ZsL and ZsR', and computes the position coordinate (Z,
.theta.y) of wafer stage WST. As a matter of course, linkage
process CH is not performed if there is no change in the
combination. Z head ZsR which is removed from the monitoring
subject, is switched to a waiting state at the time of the fourth
control clock when Z head ZsR moves off from the scanning area on
the Y scale.
[0275] Incidentally, so far, in order to describe the principle of
the switching method of the encoder to be used in position control
of wafer stage WST in the embodiment, four Z heads ZsL, ZsL', ZsR,
and ZsR' were taken up, however, ZsL and ZsL' representatively show
any of Z heads 74.sub.i (i=1 to 5), 72a, and 72b, and ZsR and ZsR'
representatively show any of Z heads 76.sub.j (j=1 to 5), 72c, and
72d. Accordingly, similar to the switching between Z heads 74.sub.i
(i=1 to 5) and 76.sub.j (j=1 to 5), the switching and linkage
process described above can be applied to the switching between Z
heads 72a to 72d, and the switching between Z heads 72a to 72d and
Z heads 74.sub.i (i=1 to 5) and 76.sub.j (j=1 to 5).
[0276] Incidentally, so far, in order to simplify the description,
while main controller 20 performed the control of each part of the
exposure apparatus including the control of the stage system (such
as reticle stage RST and wafer stage WST), interferometer system
118, encoder system 150, surface position measurement system 180
and the like, as a matter of course, at least a part of the control
of main controller 20 described above can be performed shared by a
plurality of controllers. For example, a stage controller which
performs operations such as the control of the stage, switching of
the heads of encoder system 150 and surface position measurement
system 180 can be arranged to operate under main controller 20.
Further, the control that main controller 20 performs does not
necessarily have to be realized by hardware, and main controller 20
can realize the control by software according to a computer program
that sets each operation of some controllers that perform the
control sharing as previously described.
[0277] As discussed in detail above, according to the exposure
apparatus of the embodiment, main controller 20 measures the
direction (the position in the Z-axis direction) perpendicular to
the XY plane of wafer stage WST and the tilt (.theta.y rotation)
with respect to the XY plane using surface position measurement
system 180, and with this measurement, the .theta.x rotation of
wafer stage WST is measured using Y interferometer 16. Then, main
controller 20 switches the set of Z heads used to control the
position of wafer stage WST in the Z-axis direction and the tilt
(.theta.y rotation) with respect to the XY plane to another set of
Z heads that includes at least one Z head different from the set of
Z heads above, so that the position of wafer stage WST in the
Z-axis direction and the tilt with respect to the XY plane
(.theta.y rotation and .theta.x rotation) becomes successive before
and after the switching. By this switching, although the Z head
used is sequentially changed according to the position of the wafer
table in the XY plane, the position of the wafer table in the
Z-axis direction and the tilt with respect to the XY plane
(.theta.y rotation and .theta.x rotation) is stored before and
after the switching, which makes it possible to drive wafer stage
WST with high precision.
[0278] Further, according to exposure apparatus 100 related to the
embodiment, by transferring and forming the pattern of reticle R in
each shot area on wafer W mounted on wafer stage WST which is
driven with good precision as described above, it becomes possible
to form a pattern with good precision in each shot area on wafer W.
Further, according to exposure apparatus 100 related to the
embodiment, by performing the focus leveling control of the wafer
with high accuracy during scanning exposure using the Z heads
without measuring the surface position information of the wafer
surface during exposure, based on the results of focus mapping
performed beforehand, it becomes possible to form a pattern on
wafer W with good precision. Furthermore, in the embodiment,
because a high-resolution exposure can be realized by liquid
immersion exposure, a fine pattern can be transferred with good
precision on wafer W also from this viewpoint.
[0279] Incidentally, in the embodiment above, when focus sensor FS
of each Z head performs the focus-servo previously described, the
focal point may be on the cover glass surface protecting the
diffraction grating surface formed on scales Y.sub.1 and Y.sub.2,
however, it is desirable for the focal point to be on a surface
further away than the cover glass surface, such as, on the
diffraction grating surface. With this arrangement, in the case
foreign material (dust) such as particles is on the cover glass
surface and the cover glass surface becomes a surface which is
defocused by the thickness of the cover glass, the influence of the
foreign material is less likely to affect the Z heads.
[0280] In the embodiment above, the surface position measurement
system which is configured having a plurality of Z heads arranged
exterior to wafer stage WST (the upper part) in the operating range
(a range where the device moves in the actual sequence in the
movement range) of wafer stage WST and detects the Z position of
the wafer stage WST (Y scales 39Y.sub.1 and 39Y.sub.2) surface with
each Z head was employed, however, the present invention is not
limited to this. For example, a plurality of Z heads can be placed
on an upper surface of a movable body, and a detection device,
which faces the heads and has a reflection surface arranged outside
the movable body that reflects the probe beam from the Z heads, can
be employed, instead of surface position detection system 180.
Further, in the embodiment above, an example has been described
where the encoder system is employed that has a configuration where
a grid section (a Y scale and an X scale) is arranged on a wafer
table (a wafer stage), and X heads and Y heads facing the grid
section are placed external to the wafer stage, however, the
present invention is not limited to this, and an encoder system
which is configured having an encoder head arranged on the movable
body and has a two-dimensional grid (or a linear grid section
having a two-dimensional placement) facing the encoder heads placed
external to the wafer stage can also be adopted. In this case, when
Z heads are also to be placed on the movable body upper surface,
the two-dimensional grid (or the linear grid section having a
two-dimensional placement) can also be used as a reflection surface
that reflects the probe beam from the Z heads.
[0281] Further, in the embodiment above, the case has been
described where each Z head is equipped with sensor main section ZH
(the first sensor) which houses focus sensor FS and is driven in
the Z-axis direction by the drive section (not shown), measurement
section ZE (the second sensor) which measures the displacement of
the first sensor (sensor main section ZH) in the Z-axis direction,
and the like as shown in FIG. 7, however, the present invention is
not limited to this. More specifically, with the Z head (the sensor
head), the first sensor itself does not necessarily have to be
movable in the Z-axis direction, as long as a part of the member
configuring the first sensor (for example, the focus sensor
previously described) is movable, and the part of the member moves
according to the movement of the movable body in the Z-axis
direction so that the optical positional relation (for example, a
conjugate relation with the photodetection surface (detection
surface) of the light receiving elements within the first sensor)
of the first sensor with the measurement object surface is
maintained. In such a case, the second sensor measures the
displacement in the movement direction from a reference position of
the movable member. As a matter of course, in the case a sensor
head is arranged on the movable body, the movable member should be
moved so that the optical positional relation of the measurement
object of the first sensor, such as, for example, the
two-dimensional grid described above (or the linear grid section
having a two-dimensional placement) and the like with the first
sensor is maintained, according to the position change of the
movable body in a direction perpendicular to the two-dimensional
plane.
[0282] Further, in the embodiment above, while the case has been
described where the encoder head and the Z head are separately
arranged, besides such a case, for example, a head that has both
functions of the encoder head and the Z head can be employed, or an
encoder head and a Z head that have a part of the optical system in
common can be employed, or a combined head which is integrated by
arranging the encoder head and the Z head within the same housing
can also be employed.
[0283] Incidentally, in the embodiment above, while the lower
surface of nozzle unit 32 and the lower end surface of the tip
optical element of projection optical system PL were on a
substantially flush surface, as well as this, for example, the
lower surface of nozzle unit 32 can be placed nearer to the image
plane (more specifically, to the wafer) of projection optical
system PL than the outgoing surface of the tip optical element.
That is, the configuration of local liquid immersion unit 8 is not
limited to the configuration described above, and the
configurations can be used, which are described in, for example, EP
Patent Application Publication No. 1 420 298 description, the
pamphlet of International Publication No. 2004/055803, the pamphlet
of International Publication No. 2004/057590, the pamphlet of
International. Publication No. 2005/029559 (the corresponding U.S.
Patent Application Publication No. 2006/0231206), the pamphlet of
International Publication No. 2004/086468 (the corresponding U.S.
Patent Application Publication No. 2005/0280791), the U.S. Pat. No.
6,952,253, and the like. Further, as disclosed in the pamphlet of
International Publication No. 2004/019128 (the corresponding U.S.
Patent Application Publication No. 2005/0248856), the optical path
on the object plane side of the tip optical element may also be
filled with liquid, in addition to the optical path on the image
plane side of the tip optical element. Furthermore, a thin film
that is lyophilic and/or has dissolution preventing function may
also be formed on the partial surface (including at least a contact
surface with liquid) or the entire surface of the tip optical
element. Incidentally, quartz has a high affinity for liquid, and
also needs no dissolution preventing film, while in the case of
fluorite, at least a dissolution preventing film is preferably
formed.
[0284] Incidentally, in the embodiment above, pure water (water)
was used as the liquid, however, it is a matter of course that the
present invention is not limited to this. As the liquid, liquid
that is chemically stable, having high transmittance to
illumination light IL and safe to use, such as a
fluorine-containing inert liquid may be used. As the
fluorine-containing inert liquid, for example, Fluorinert (the
brand name of 3M United States) can be used. The
fluorine-containing inert liquid is also excellent from the point
of cooling effect. Further, as the liquid, liquid which has a
refractive index higher than pure water (a refractive index is
around 1.44), for example, liquid having a refractive index equal
to or higher than 1.5 can be used. As this type of liquid, for
example, a predetermined liquid having C--H binding or O--H binding
such as isopropanol having a refractive index of about 1.50,
glycerol (glycerin) having a refractive index of about 1.61, a
predetermined liquid (organic solvent) such as hexane, heptane or
decane, or decalin (decahydronaphthalene) having a refractive index
of about 1.60, or the like can be cited. Alternatively, a liquid
obtained by mixing arbitrary two or more of these liquids may be
used, or a liquid obtained by adding (mixing) at least one of these
liquids to (with) pure water may be used. Alternatively, as the
liquid, a liquid obtained by adding (mixing) base or acid such as
H.sup.+, Cs.sup.+, K.sup.+, Cl.sup.-, SO.sub.4.sup.2-, or
PO.sub.4.sup.2- to (with) pure water can be used. Moreover, a
liquid obtained by adding (mixing) particles of Al oxide or the
like to (with) pure water can be used. These liquids can transmit
ArF excimer laser light. Further, as the liquid, liquid, which has
a small absorption coefficient of light, is less
temperature-dependent, and is stable to a projection optical system
(tip optical member) and/or a photosensitive agent (or a protection
film (top coat film), an antireflection film, or the like) coated
on the surface of a wafer, is preferable. Further, in the case an
F.sub.2 laser is used as the light source, fomblin oil can be
selected. Further, as the liquid, a liquid having a higher
refractive index to illumination light IL than that of pure water,
for example, a refractive index of around 1.6 to 1.8 may be used.
As the liquid, supercritical fluid can also be used. Further, the
tip optical element of projection optical system PL may be formed
by quartz (silica), or single-crystal materials of fluoride
compound such as calcium fluoride (fluorite), barium fluoride,
strontium fluoride, lithium fluoride, and sodium fluoride, or may
be formed by materials having a higher refractive index than that
of quartz or fluorite (e.g. equal to or higher than 1.6). As the
materials having a refractive index equal to or higher than 1.6,
for example, sapphire, germanium dioxide, or the like disclosed in
the pamphlet of International Publication No. 2005/059617, or
kalium chloride (having a refractive index of about 1.75) or the
like disclosed in the pamphlet of International Publication No.
2005/059618 can be used.
[0285] Further, in the embodiment above, the recovered liquid may
be reused, and in this case, a filter that removes impurities from
the recovered liquid is preferably arranged in a liquid recovery
unit, a recovery pipe or the like.
[0286] Incidentally, in the embodiment above, the case has been
described where the exposure apparatus is a liquid immersion type
exposure apparatus. However, the present invention is not limited
to this, but can also be employed in a dry type exposure apparatus
that performs exposure of wafer W without liquid (water).
[0287] Further, in the embodiment above, the case has been
described where the present invention is applied to a scanning
exposure apparatus by a step-and-scan method or the like. However,
the present invention is not limited to this, but may also be
applied to a static exposure apparatus such as a stepper. Further,
the present invention can also be applied to a reduction projection
exposure apparatus by a step-and-stitch method that synthesizes a
shot area and a shot area, an exposure apparatus by a proximity
method, a mirror projection aligner, or the like. Moreover, the
present invention can also be applied to a multi-stage type
exposure apparatus equipped with a plurality of wafer stage WSTs,
as is disclosed in, for example, the U.S. Pat. No. 6,590,634, the
U.S. Pat. No. 5,969,441, the U.S. Pat. No. 6,208,407 and the
like.
[0288] Further, the magnification of the projection optical system
in the exposure apparatus of the embodiment above is not only a
reduction system, but also may be either an equal magnifying system
or a magnifying system, and projection optical system PL is not
only a dioptric system, but also may be either a catoptric system
or a catadioptric system, and in addition, the projected image may
be either an inverted image or an upright image. Moreover, exposure
area IA to which illumination light IL is irradiated via projection
optical system PL is an on-axis area that includes optical axis AX
within the field of projection optical system PL. However, for
example, as is disclosed in the pamphlet of International
Publication No. 2004/107011, exposure area IA may also be an
off-axis area that does not include optical axis AX, similar to a
so-called inline type catadioptric system, in part of which an
optical system (catoptric system or catadioptric system) that has
plural reflection surfaces and forms an intermediate image at least
once is arranged, and which has a single optical axis. Further, the
illumination area and exposure area described above are to have a
rectangular shape. However, the shape is not limited to
rectangular, and can also be circular arc, trapezoidal,
parallelogram or the like.
[0289] Incidentally, a light source of the exposure apparatus in
the embodiment above is not limited to the ArF excimer laser, but a
pulse laser light source such as a KrF excimer laser (output
wavelength: 248 nm), an F.sub.2 laser (output wavelength: 157 nm),
an Ar.sub.2 laser (output wavelength: 126 nm) or a Kr.sub.2 laser
(output wavelength: 146 nm), or an extra-high pressure mercury lamp
that generates an emission line such as a g-line (wavelength: 436
nm) or an i-line (wavelength: 365 nm) can also be used. Further, a
harmonic wave generating unit of a YAG laser or the like can also
be used. Besides the sources above, as is disclosed in, for
example, the pamphlet of International Publication No. 99/46835
(the corresponding U.S. Pat. No. 7,023,610), a harmonic wave, which
is obtained by amplifying a single-wavelength laser beam in the
infrared or visible range emitted by a DFB semiconductor laser or
fiber laser as vacuum ultraviolet light, with a fiber amplifier
doped with, for example, erbium (or both erbium and ytterbium), and
by converting the wavelength into ultraviolet light using a
nonlinear optical crystal, can also be used.
[0290] Further, in the embodiment above, illumination light IL of
the exposure apparatus is not limited to the light having a
wavelength equal to or more than 100 nm, and it is needless to say
that the light having a wavelength less than 100 nm can be used.
For example, in recent years, in order to expose a pattern equal to
or less than 70 nm, an EUV exposure apparatus that makes an SOR or
a plasma laser as a light source generate an EUV (Extreme
Ultraviolet) light in a soft X-ray range (e.g. a wavelength range
from 5 to 15 nm), and uses a total reflection reduction optical
system designed under the exposure wavelength (e.g. 13.5 nm) and
the reflective mask has been developed. In the EUV exposure
apparatus, the arrangement in which scanning exposure is performed
by synchronously scanning a mask and a wafer using a circular arc
illumination can be considered, and therefore, the present
invention can also be suitably applied to such an exposure
apparatus. Besides such an apparatus, the present invention can
also be applied to an exposure apparatus that uses charged particle
beams such as an electron beam or an ion beam.
[0291] Further, in the embodiment above, a transmissive type mask
(reticle) is used, which is a transmissive substrate on which a
predetermined light shielding pattern (or a phase pattern or a
light attenuation pattern) is formed. Instead of this reticle,
however, as is disclosed in, for example, U.S. Pat. No. 6,778,257,
an electron mask (which is also called a variable shaped mask, an
active mask or an image generator, and includes, for example, a DMD
(Digital Micromirror Device) that is a type of a non-emission type
image display device (spatial light modulator) or the like) on
which a light-transmitting pattern, a reflection pattern, or an
emission pattern is formed according to electronic data of the
pattern that is to be exposed may also be used.
[0292] Further, as is disclosed in, for example, the pamphlet of
International Publication No. 2001/035168, the present invention
can also be applied to an exposure apparatus (lithography system)
that forms line-and-space patterns on a wafer by forming
interference fringes on the wafer.
[0293] Moreover, the present invention can also be applied to an
exposure apparatus that synthesizes two reticle patterns via a
projection optical system and almost simultaneously performs double
exposure of one shot area by one scanning exposure, as is disclosed
in, for example, Kohyo (published Japanese translation of
International Publication for Patent Application) No. 2004-519850
(the corresponding U.S. Pat. No. 6,611,316).
[0294] Further, an apparatus that forms a pattern on an object is
not limited to the exposure apparatus (lithography system)
described above, and for example, the present invention can also be
applied to an apparatus that forms a pattern on an object by an
ink-jet method.
[0295] Incidentally, an object on which a pattern is to be formed
(an object subject to exposure to which an energy beam is
irradiated) in the embodiment above is not limited to a wafer, but
may be other objects such as a glass plate, a ceramic substrate, a
film member, or a mask blank.
[0296] The use of the exposure apparatus is not limited only to the
exposure apparatus for manufacturing semiconductor devices, but the
present invention can also be widely applied, for example, to an
exposure apparatus for transferring a liquid crystal display device
pattern onto a rectangular glass plate, and an exposure apparatus
for producing organic ELs, thin-film magnetic heads, imaging
devices (such as CCDs), micromachines, DNA chips, and the like.
Further, the present invention can be applied not only to an
exposure apparatus for producing microdevices such as semiconductor
devices, but can also be applied to an exposure apparatus that
transfers a circuit pattern onto a glass plate or silicon wafer to
produce a mask or reticle used in a light exposure apparatus, an
EUV exposure apparatus, an X-ray exposure apparatus, an
electron-beam exposure apparatus, and the like.
[0297] Incidentally, the movable body drive system and the movable
body drive method of the present invention can be applied not only
to the exposure apparatus, but can also be applied widely to other
substrate processing apparatuses (such as a laser repair apparatus,
a substrate inspection apparatus and the like), or to apparatuses
equipped with a movable body such as a stage that moves within a
two-dimensional plane such as a position setting apparatus for
specimen or a wire bonding apparatus in other precision
machines.
[0298] Incidentally, the disclosures of the various publications
(descriptions), the pamphlets of the International Publications,
and the U.S. patent application Publication descriptions and the
U.S. patent descriptions that are cited in the embodiment above and
related to exposure apparatuses and the like are each incorporated
herein by reference.
[0299] Semiconductor devices are manufactured through the following
steps: a step where the function/performance design of the device
is performed, a step where a wafer is made using silicon materials,
a lithography step where the pattern formed on a reticle (mask) by
the exposure apparatus (pattern formation apparatus) in the
embodiment previously described is transferred onto a wafer, a
development step where the wafer that has been exposed is
developed, an etching step where an exposed member of an area other
than the area where the resist remains is removed by etching, a
resist removing step where the resist that is no longer necessary
when etching has been completed is removed, a device assembly step
(including processes such as a dicing process, a bonding process,
and a packaging process), inspection steps and the like.
[0300] By using the device manufacturing method of the embodiment
described above, because the exposure apparatus (pattern formation
apparatus) in the embodiment above and the exposure method (pattern
formation method) thereof are used in the exposure step, exposure
with high throughput can be performed while maintaining the high
overlay accuracy. Accordingly, the productivity of highly
integrated microdevices on which fine patterns are formed can be
improved.
[0301] While the above-described embodiment of the present
invention is the presently preferred embodiment thereof, those
skilled in the art of lithography systems will readily recognize
that numerous additions, modifications, and substitutions may be
made to the above-described embodiment without departing from the
spirit and scope thereof. It is intended that all such
modifications, additions, and substitutions fall within the scope
of the present invention, which is best defined by the claims
appended below.
* * * * *