U.S. patent application number 11/025603 was filed with the patent office on 2006-07-06 for lithographic apparatus and device manufacturing method.
This patent application is currently assigned to ASML NETHERLANDS B.V.. Invention is credited to Johannes Jacobus Matheus Baselmans, Sjoerd Nicolaas Lambertus Donders, Christiaan Alexander Hoogendam, Jeroen Johannes Sophia Maria Mertens, Johannes Catharinus Hubertus Mulkens, Bob Streefkerk.
Application Number | 20060147821 11/025603 |
Document ID | / |
Family ID | 35790378 |
Filed Date | 2006-07-06 |
United States Patent
Application |
20060147821 |
Kind Code |
A1 |
Streefkerk; Bob ; et
al. |
July 6, 2006 |
Lithographic apparatus and device manufacturing method
Abstract
A method for correcting an exposure parameter of an immersion
lithographic apparatus is provided. In the method, an exposure
parameter is measured using a measuring beam projected through a
liquid between the projection system and a substrate table of the
immersion lithographic apparatus and offset is determined based on
a change of a physical property impacting a measurement made using
the measuring beam to at least partly correct the measured exposure
parameter.
Inventors: |
Streefkerk; Bob; (Tilburg,
NL) ; Baselmans; Johannes Jacobus Matheus; (Oirschot,
NL) ; Donders; Sjoerd Nicolaas Lambertus;
('s-Hertogenbosch, NL) ; Mertens; Jeroen Johannes Sophia
Maria; (Duizel, NL) ; Mulkens; Johannes Catharinus
Hubertus; (Waalre, NL) ; Hoogendam; Christiaan
Alexander; (Veldhoven, NL) |
Correspondence
Address: |
PILLSBURY WINTHROP SHAW PITTMAN, LLP
P.O. BOX 10500
MCLEAN
VA
22102
US
|
Assignee: |
ASML NETHERLANDS B.V.
Veldhoven
NL
|
Family ID: |
35790378 |
Appl. No.: |
11/025603 |
Filed: |
December 30, 2004 |
Current U.S.
Class: |
430/30 ; 355/18;
430/22 |
Current CPC
Class: |
G03F 7/70883 20130101;
G03F 9/7023 20130101; G03F 7/70341 20130101 |
Class at
Publication: |
430/030 ;
355/018; 430/022 |
International
Class: |
G03B 27/00 20060101
G03B027/00; G03F 9/00 20060101 G03F009/00; G03C 5/00 20060101
G03C005/00 |
Claims
1. A method for correcting an exposure parameter of an immersion
lithographic apparatus, the method comprising: measuring an
exposure parameter using a measuring beam projected through a
liquid between the projection system and a substrate table of the
immersion lithographic apparatus; and determining an offset based
on a change of a physical property impacting a measurement made
using the measuring beam to at least partly correct the measured
exposure parameter.
2. The method according to claim 1, wherein the physical property
comprises (a) a temperature, or (b) a pressure, or (c) a
composition, or (d) any combination of (a)-(c), of the liquid.
3. The method according to claim 1, wherein the physical property
comprises (a) a temperature, or (b) a pressure, or (c) a
composition, or (d) any combination of (a)-(c), of a flushing gas,
on an optical element of the projection system, or both.
4. The method according to claim 1, wherein the exposure parameter
comprises a focus of a patterned beam to be projected using the
projection system, a height of the substrate held on the substrate
table, or both.
5. The method according to claim 1, wherein the exposure parameter
comprises a lateral placement of a patterned beam to be projected
using the projection system, an X-Y position of the substrate held
on the substrate table, or both.
6. The method according to claim 1, wherein the physical property
comprises a wavelength of the measuring beam, a wavelength of a
patterned beam to be projected using the projection system, or
both.
7. The method according to claim 1, wherein the offset comprises a
multiplication of the change of the physical property and a rate of
change of the exposure parameter with respect to the physical
property.
8. The method according to claim 1, comprising projecting the
measuring beam and a patterned beam for the exposure of the
substrate through an optical element of the projection system.
9. The method according to claim 1, wherein determining the offset
based on the change of the physical property comprises determining
the offset based on the difference between the change of the
physical property for a wavelength of the measuring beam and a
change of the physical property for a wavelength of a patterned
beam to be projected using the projection system.
10. A lithographic apparatus, comprising: a support structure
configured to hold a patterning device, the patterning device
configured to impart a beam of radiation with a pattern in its
cross-section; a substrate table configured to hold a substrate; a
projection system configured to project the patterned beam onto a
target portion of the substrate; a liquid supply system configured
to provide liquid to a space between the projection system and the
substrate table; a sensor configured to measure an exposure
parameter using a measuring beam projected through the liquid; and
a correction system configured to determine an offset based on a
change of a physical property impacting a measurement made using
the measuring beam to at least partly correct the measured exposure
parameter.
11. The apparatus according to claim 10, wherein the physical
property comprises (a) a temperature, or (b) a pressure, or (c) a
composition, or (d) any combination of (a)-(c), of the liquid.
12. The apparatus according to claim 10, wherein the physical
property comprises (a) a temperature, or (b) a pressure, or (c) a
composition, or (d) any combination of (a)-(c), of a flushing gas,
on an optical element of the projection system, or both.
13. The apparatus according to claim 11, further comprising a
temperature sensor configured to measure the temperature of the
liquid, a pressure sensor configured to measure the pressure of the
liquid, or both.
14. The apparatus according to claim 10, wherein the exposure
parameter comprises a focus of the patterned beam, a height of the
substrate, or both.
15. The apparatus according to claim 10, wherein the exposure
parameter comprises a lateral placement of the patterned beam, an
X-Y position of the substrate, or both.
16. The apparatus according to claim 10, wherein the physical
property comprises a wavelength of the measuring beam, the
patterned beam, or both.
17. The apparatus according to claim 10, wherein the offset
comprises a multiplication of the change of the physical property
and a rate of change of the exposure parameter with respect to the
physical property.
18. The apparatus according to claim 10, wherein sensor is
configured to project the measuring beam through an optical of the
projection system through the patterned beam is to be
projected.
19. The apparatus according to claim 10, wherein the correction
system is configured to determine the offset based on the
difference between the change of the physical property for a
wavelength of the measuring beam and a change of the physical
property for a wavelength of the patterned beam.
20. A computer program product for correcting an exposure parameter
of an immersion lithographic apparatus, comprising: software code
configured to measure an exposure parameter using a measuring beam
projected through a liquid between the projection system and a
substrate table of the immersion lithographic apparatus; and
software code configured to determine an offset based on a change
of a physical property impacting a measurement made using the
measuring beam to at least partly correct the measured exposure
parameter.
21. The computer program product according to claim 20, wherein the
physical property comprises (a) a temperature, or (b) a pressure,
or (c) a composition, or (d) any combination of (a)-(c), of the
liquid.
22. The computer program product according to claim 20, wherein the
physical property comprises (a) a temperature, or (b) a pressure,
or (c) a composition, or (d) any combination of (a)-(c), of a
flushing gas, on an optical element of the projection system, or
both.
23. The computer program product according to claim 20, wherein the
exposure parameter comprises a focus of a patterned beam to be
projected using the projection system, a height of a substrate held
on the substrate table, or both.
24. The computer program product according to claim 20, wherein the
exposure parameter comprises a lateral placement of a patterned
beam to be projected using the projection system, an X-Y position
of a substrate held on the substrate table, or both.
25. The computer program product according to claim 20, wherein the
physical property comprises a wavelength of the measuring beam, a
wavelength of a patterned beam to be projected using the projection
system, or both.
26. The computer program product according to claim 20, comprising
software code configured to determine the offset by multiplication
of the change of the physical property and a rate of change of the
exposure parameter with respect to the physical property.
27. The computer program product according to claim 20, comprising
software code configured to determine the offset based on the
difference between the change of the physical property for a
wavelength of the measuring beam and a change of the physical
property for a wavelength of a patterned beam to be projected using
the projection system.
Description
FIELD
[0001] The invention relates to a lithographic apparatus and a
method for manufacturing a device.
BACKGROUND
[0002] A lithographic apparatus is a machine that applies a desired
pattern onto a substrate, usually onto a target portion of the
substrate. A lithographic apparatus can be used, for example, in
the manufacture of integrated circuits (ICs). In that instance, a
patterning device, which is alternatively referred to as a mask or
a reticle, may be used to generate a circuit pattern to be formed
on an individual layer of the IC. This pattern can be transferred
onto a target portion (e.g. comprising part of, one, or several
dies) on a substrate (e.g. a silicon wafer). Transfer of the
pattern is typically via imaging onto a layer of
radiation-sensitive material (resist) provided on the substrate. In
general, a single substrate will contain a network of adjacent
target portions that are successively patterned. Known lithographic
apparatus include so-called steppers, in which each target portion
is irradiated by exposing an entire pattern onto the target portion
at one time, and so-called scanners, in which each target portion
is irradiated by scanning the pattern through a radiation beam in a
given direction (the "scanning"-direction) while synchronously
scanning the substrate parallel or anti-parallel to this direction.
It is also possible to transfer the pattern from the patterning
device to the substrate by imprinting the pattern onto the
substrate.
[0003] It has been proposed to immerse the substrate in the
lithographic projection apparatus in a liquid having a relatively
high refractive index, e.g. water, so as to fill a space between
the final element of the projection system and the substrate. The
point of this is to enable imaging of smaller features since the
exposure radiation will have a shorter wavelength in the liquid.
(The effect of the liquid may also be regarded as increasing the
effective numerical aperature (NA) of the system and also
increasing the depth of focus.) Other immersion liquids have been
proposed, including water with solid particles (e.g. quartz)
suspended therein.
[0004] However, submersing the substrate or substrate and substrate
table in a bath of liquid (see, for example, U.S. Pat. No.
4,509,852, hereby incorporated in its entirety by reference) means
that there is a large body of liquid that must be accelerated
during a scanning exposure. This requires additional or more
powerful motors and turbulence in the liquid may lead to
undesirable and unpredictable effects.
[0005] One of the solutions proposed is for a liquid supply system
to provide liquid on only a localized area of the substrate and in
between the final element of the projection system and the
substrate (the substrate generally has a larger surface area than
the final element of the projection system). One way which has been
proposed to arrange for this is disclosed in PCT patent application
no. WO 99/49504, hereby incorporated in its entirety by reference.
As illustrated in FIGS. 2 and 3, liquid is supplied by at least one
inlet IN onto the substrate, preferably along the direction of
movement of the substrate relative to the final element, and is
removed by at least one outlet OUT after having passed under the
projection system. That is, as the substrate is scanned beneath the
element in a -X direction, liquid is supplied at the +X side of the
element and taken up at the -X side. FIG. 2 shows the arrangement
schematically in which liquid is supplied via inlet IN and is taken
up on the other side of the element by outlet OUT which is
connected to a low pressure source. In the illustration of FIG. 2
the liquid is supplied along the direction of movement of the
substrate relative to the final element, though this does not need
to be the case. Various orientations and numbers of in- and
out-lets positioned around the final element are possible, one
example is illustrated in FIG. 3 in which four sets of an inlet
with an outlet on either side are provided in a regular pattern
around the final element.
SUMMARY
[0006] It would be advantageous, for example, to provide a method,
apparatus and/or computer program product for correcting an
exposure parameter of an immersion lithographic apparatus.
[0007] According to an aspect of the invention, there is provided a
method for correcting an exposure parameter of an immersion
lithographic apparatus, the method comprising:
[0008] measuring an exposure parameter using a measuring beam
projected through a liquid between the projection system and a
substrate table of the immersion lithographic apparatus; and
[0009] determining an offset based on a change of a physical
property impacting a measurement made using the measuring beam to
at least partly correct the measured exposure parameter.
[0010] According to an aspect of the invention, there is provided a
lithographic apparatus, comprising:
[0011] a support structure configured to hold a patterning device,
the patterning device configured to impart a beam of radiation with
a pattern in its cross-section;
[0012] a substrate table configured to hold a substrate;
[0013] a projection system configured to project the patterned beam
onto a target portion of the substrate;
[0014] a liquid supply system configured to provide liquid to a
space between the projection system and the substrate table;
[0015] a sensor configured to measure an exposure parameter using a
measuring beam projected through the liquid; and
[0016] a correction system configured to determine an offset based
on a change of a physical property impacting a measurement made
using the measuring beam to at least partly correct the measured
exposure parameter.
[0017] According to an aspect of the invention, there is provided a
computer program product for correcting an exposure parameter of an
immersion lithographic apparatus, comprising:
[0018] software code configured to measure an exposure parameter
using a measuring beam projected through a liquid between the
projection system and a substrate table of the immersion
lithographic apparatus; and
[0019] software code configured to determine an offset based on a
change of a physical property impacting a measurement made using
the measuring beam to at least partly correct the measured exposure
parameter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Embodiments of the invention will now be described, by way
of example only, with reference to the accompanying schematic
drawings in which corresponding reference symbols indicate
corresponding parts, and in which:
[0021] FIG. 1 depicts a lithographic apparatus according to an
embodiment of the invention;
[0022] FIGS. 2 and 3 depict a liquid supply system for use in a
lithographic projection apparatus;
[0023] FIG. 4 depicts another liquid supply system for use in a
lithographic projection apparatus;
[0024] FIG. 5 depicts another liquid supply system for use in a
lithographic projection apparatus;
[0025] FIG. 6 schematically depicts passage of a radiation beam
through an optical element of the projection system of a
lithographic apparatus according to an embodiment of the invention;
and
[0026] FIG. 7 depicts a flow chart of a method according to an
embodiment of the invention.
DETAILED DESCRIPTION
[0027] FIG. 1 schematically depicts a lithographic apparatus
according to one embodiment of the invention. The apparatus
comprises:
[0028] an illumination system (illuminator) IL configured to
condition a radiation beam PB (e.g. UV radiation or DUV
radiation);
[0029] a support structure (e.g. a mask table) MT constructed to
support a patterning device (e.g. a mask) MA and connected to a
first positioner PM configured to accurately position the
patterning device in accordance with certain parameters;
[0030] a substrate table (e.g. a wafer table) WT constructed to
hold a substrate (e.g. a resist-coated wafer) W and connected to a
second positioner PW configured to accurately position the
substrate in accordance with certain parameters; and
[0031] a projection system (e.g. a refractive projection lens
system) PL configured to project a pattern imparted to the
radiation beam PB by patterning device MA onto a target portion C
(e.g. comprising one or more dies) of the substrate W.
[0032] The illumination system may include various types of optical
components, such as refractive, reflective, magnetic,
electromagnetic, electrostatic or other types of optical
components, or any combination thereof, for directing, shaping, or
controlling radiation.
[0033] The support structure supports, i.e. bears the weight of,
the patterning device. It holds the patterning device in a manner
that depends on the orientation of the patterning device, the
design of the lithographic apparatus, and other conditions, such as
for example whether or not the patterning device is held in a
vacuum environment. The support structure can use mechanical,
vacuum, electrostatic or other clamping techniques to hold the
patterning device. The support structure may be a frame or a table,
for example, which may be fixed or movable as required. The support
structure may ensure that the patterning device is at a desired
position, for example with respect to the projection system. Any
use of the terms "reticle" or "mask" herein may be considered
synonymous with the more general term "patterning device."
[0034] The term "patterning device" used herein should be broadly
interpreted as referring to any device that can be used to impart a
radiation beam with a pattern in its cross-section such as to
create a pattern in a target portion of the substrate. It should be
noted that the pattern imparted to the radiation beam may not
exactly correspond to the desired pattern in the target portion of
the substrate, for example if the pattern includes phase-shifting
features or so called assist features. Generally, the pattern
imparted to the radiation beam will correspond to a particular
functional layer in a device being created in the target portion,
such as an integrated circuit.
[0035] The patterning device may be transmissive or reflective.
Examples of patterning devices include masks, programmable mirror
arrays, and programmable LCD panels. Masks are well known in
lithography, and include mask types such as binary, alternating
phase-shift, and attenuated phase-shift, as well as various hybrid
mask types. An example of a programmable mirror array employs a
matrix arrangement of small mirrors, each of which can be
individually tilted so as to reflect an incoming radiation beam in
different directions. The tilted mirrors impart a pattern in a
radiation beam which is reflected by the mirror matrix.
[0036] The term "projection system" used herein should be broadly
interpreted as encompassing any type of projection system,
including refractive, reflective, catadioptric, magnetic,
electromagnetic and electrostatic optical systems, or any
combination thereof, as appropriate for the exposure radiation
being used, or for other factors such as the use of an immersion
liquid or the use of a vacuum. Any use of the term "projection
lens" herein may be considered as synonymous with the more general
term "projection system".
[0037] As here depicted, the apparatus is of a transmissive type
(e.g. employing a transmissive mask). Alternatively, the apparatus
may be of a reflective type (e.g. employing a programmable mirror
array of a type as referred to above, or employing a reflective
mask).
[0038] The lithographic apparatus may be of a type having two (dual
stage) or more substrate tables (and/or two or more mask tables).
In such "multiple stage" machines, the additional tables may be
used in parallel, or preparatory steps may be carried out on one or
more tables while one or more other tables are being used for
exposure.
[0039] Referring to FIG. 1, the illuminator IL receives a radiation
beam from a radiation source SO. The source and the lithographic
apparatus may be separate entities, for example when the source is
an excimer laser. In such cases, the source is not considered to
form part of the lithographic apparatus and the radiation beam is
passed from the source SO to the illuminator IL with the aid of a
beam delivery system BD comprising, for example, suitable directing
mirrors and/or a beam expander. In other cases the source may be an
integral part of the lithographic apparatus, for example when the
source is a mercury lamp. The source SO and the illuminator IL,
together with the beam delivery system BD if required, may be
referred to as a radiation system.
[0040] The illuminator IL may comprise an adjuster AD for adjusting
the angular intensity distribution of the radiation beam.
Generally, at least the outer and/or inner radial extent (commonly
referred to as .sigma.-outer and .sigma.-inner, respectively) of
the intensity distribution in a pupil plane of the illuminator can
be adjusted. In addition, the illuminator IL may comprise various
other components, such as an integrator IN and a condenser CO. The
illuminator may be used to condition the radiation beam, to have a
desired uniformity and intensity distribution in its
cross-section.
[0041] The radiation beam PB is incident on the patterning device
(e.g., mask MA), which is held on the support structure (e.g., mask
table MT), and is patterned by the patterning device. Having
traversed the mask MA, the radiation beam PB passes through the
projection system PL, which focuses the beam onto a target portion
C of the substrate W. An immersion hood IH, which is described
further below, supplies immersion liquid to a space between the
final element of the projection system PL and the substrate W.
[0042] With the aid of the second positioner PW and position sensor
IF (e.g. an interferometric device, linear encoder or capacitive
sensor), the substrate table WT can be moved accurately, e.g. so as
to position different target portions C in the path of the
radiation beam PB. Similarly, the first positioner PM and another
position sensor (which is not explicitly depicted in FIG. 1) can be
used to accurately position the mask MA with respect to the path of
the radiation beam PB, e.g. after mechanical retrieval from a mask
library, or during a scan. In general, movement of the mask table
MT may be realized with the aid of a long-stroke module (coarse
positioning) and a short-stroke module (fine positioning), which
form part of the first positioner PM. Similarly, movement of the
substrate table WT may be realized using a long-stroke module and a
short-stroke module, which form part of the second positioner PW.
In the case of a stepper (as opposed to a scanner) the mask table
MT may be connected to a short-stroke actuator only, or may be
fixed. Mask MA and substrate W may be aligned using mask alignment
marks M1, M2 and substrate alignment marks P1, P2. Although the
substrate alignment marks as illustrated occupy dedicated target
portions, they may be located in spaces between target portions
(these are known as scribe-lane alignment marks). Similarly, in
situations in which more than one die is provided on the mask MA,
the mask alignment marks may be located between the dies.
[0043] The depicted apparatus could be used in at least one of the
following modes:
[0044] 1. In step mode, the mask table MT and the substrate table
WT are kept essentially stationary, while an entire pattern
imparted to the radiation beam is projected onto a target portion C
at one time (i.e. a single static exposure). The substrate table WT
is then shifted in the X and/or Y direction so that a different
target portion C can be exposed. In step mode, the maximum size of
the exposure field limits the size of the target portion C imaged
in a single static exposure.
[0045] 2. In scan mode, the mask table MT and the substrate table
WT are scanned synchronously while a pattern imparted to the
radiation beam is projected onto a target portion C (i.e. a single
dynamic exposure). The velocity and direction of the substrate
table WT relative to the mask table MT may be determined by the
(de-)magnification and image reversal characteristics of the
projection system PL. In scan mode, the maximum size of the
exposure field limits the width (in the non-scanning direction) of
the target portion in a single dynamic exposure, whereas the length
of the scanning motion determines the height (in the scanning
direction) of the target portion.
[0046] 3. In another mode, the mask table MT is kept essentially
stationary holding a programmable patterning device, and the
substrate table WT is moved or scanned while a pattern imparted to
the radiation beam is projected onto a target portion C. In this
mode, generally a pulsed radiation source is employed and the
programmable patterning device is updated as required after each
movement of the substrate table WT or in between successive
radiation pulses during a scan. This mode of operation can be
readily applied to maskless lithography that utilizes programmable
patterning device, such as a programmable mirror array of a type as
referred to above.
[0047] Combinations and/or variations on the above described modes
of use or entirely different modes of use may also be employed.
[0048] A further immersion lithography solution with a localized
liquid supply system is shown in FIG. 4. Liquid is supplied by two
groove inlets IN on either side of the projection system PL and is
removed by a plurality of discrete outlets OUT arranged radially
outwardly of the inlets IN. The inlets IN and OUT can be arranged
in a plate with a hole in its center and through which the
projection beam is projected. Liquid is supplied by one groove
inlet IN on one side of the projection system PL and removed by a
plurality of discrete outlets OUT on the other side of the
projection system PL, causing a flow of a thin film of liquid
between the projection system PL and the substrate W. The choice of
which combination of inlet IN and outlets OUT to use can depend on
the direction of movement of the substrate W (the other combination
of inlet IN and outlets OUT being inactive).
[0049] Another immersion lithography solution with a localized
liquid supply system solution which has been proposed is to provide
the liquid supply system with a liquid confinement structure which
extends along at least a part of a boundary of the space between
the final element of the projection system and the substrate table.
Such a solution is illustrated in FIG. 5. The liquid confinement
structure is substantially stationary relative to the projection
system in the XY plane though there may be some relative movement
in the Z direction (in the direction of the optical axis). See, for
example U.S. patent application No. 10/844,575, hereby incorporated
in its entirety by reference. A seal is formed between the liquid
confinement structure and the surface of the substrate.
[0050] Referring to FIG. 5, reservoir 10 forms a contactless seal
to the substrate around the image field of the projection system so
that liquid is confined to fill a space between the substrate
surface and the final element of the projection system. The
reservoir is formed by a liquid confinement structure 12 positioned
below and surrounding the final element of the projection system
PL. Liquid is brought into the space below the projection system
and within the liquid confinement structure 12. The liquid
confinement structure 12 extends a little above the final element
of the projection system and the liquid level rises above the final
element so that a buffer of liquid is provided. The liquid
confinement structure 12 has an inner periphery that at the upper
end, in an embodiment, closely conforms to the shape of the
projection system or the final element thereof and may, e.g., be
round. At the bottom, the inner periphery closely conforms to the
shape of the image field, e.g., rectangular though this need not be
the case.
[0051] The liquid is confined in the reservoir by a gas seal 16
between the bottom of the liquid confinement structure 12 and the
surface of the substrate W. The gas seal is formed by gas, e.g. air
or synthetic air but, in an embodiment, N.sub.2 or another inert
gas, provided under pressure via inlet 15 to the gap between liquid
confinement structure 12 and substrate and extracted via first
outlet 14. The overpressure on the gas inlet 15, vacuum level on
the first outlet 14 and geometry of the gap are arranged so that
there is a high-velocity gas flow inwards that confines the liquid.
Such a system is disclosed in U.S. patent application Ser. No.
10/705,783, hereby incorporated in its entirety by reference.
[0052] In an embodiment, to facilitate imaging of the substrate,
the leveling and alignment of the substrate may be performed at an
exposure position of the substrate. In other words, a substrate
level sensor (used to facilitate focus of a patterned projection
beam on the substrate) and a substrate alignment sensor (used to
facilitate proper lateral positioning of the substrate relative to
the patterned projection beam) are provided around the projection
system and/or the substrate positioned adjacent the projection
system, so that the substrate can be measured when the substrate
moves relative to and near the projection system during exposure.
In an immersion lithography apparatus, with the structure used to
provide or maintain liquid between the projection system and the
substrate, the amount of physical space remaining to permit the
provision or operation of one or both of those sensors is very
limited. Such space may be even more at a premium with larger
projection systems such as those having high numerical apertures
(NA), such as about 1.3. Therefore, according to an embodiment,
where the level sensor and/or the alignment sensor use a measuring
radiation beam, the measuring radiation beam may wholly or partly
pass through the projection system.
[0053] FIG. 6 schematically depicts passage of a patterned
projection beam and a measuring beam through an optical element of
the projection system of an immersion lithographic apparatus
according to an embodiment of the invention. A portion of an
example projection system PL is shown. Liquid 11 is disposed
between the projection system PL and the substrate W. A patterned
projection beam 20 is shown as entering the portion of the
projection system PL at two points (although as will be apparent,
these are just 2 rays representative of a wave). The patterned
projection beam 20 passes through the portion of the projection
system PL, then through the liquid 11, and is focused onto the
substrate W.
[0054] In this example, an incoming level sensor measuring beam 22
(e.g., provided by one or more laser sources, light emitting
diodes, (halogen) lamps, etc.) is shown entering the portion of the
projection system PL. The measuring beam passes through the portion
of the projection system PL and then through the liquid 11 onto the
substrate. The measuring beam reflects off the substrate W and then
passes, as an outgoing level sensor measuring beam 24, through the
liquid 11 and the portion of the projection system PL out to a
level sensor detector (not shown). While a level sensor measuring
beam is shown and described in FIG. 6, the measuring beam may
instead or additionally be an alignment sensor measuring beam or
any other measuring beam.
[0055] While the patterned projection beam 20 and the level sensor
measuring beam 22,24 are shown as focused at substantially the same
point on the substrate to facilitate accurate leveling/focus
measurements, the beams need not be focused at the substantially
same point. For example, the level sensor measuring beam 22,24 may
be focused at a position in advance of where the patterned
projection beam 20 will be focused so that leveling/focusing
calculations and adjustments can be made in advance of the
patterned beam projection beam 20 impinging the substrate W. Where
the measuring beam 22, 24 is, for example, an alignment beam, the
measuring beam 22, 24 may be focused at a different position, for
example, at an alignment mark, than the patterned projection beam
20.
[0056] Since a measuring beam should not expose the radiation
sensitive material of the substrate W, the wavelength of the
radiation used for the measuring beam is selected not to expose the
radiation sensitive material and thus is typically different than
the wavelength of the radiation of the patterned projection beam.
For example, in the case of a level sensor measuring beam, for
rough capturing, HeNe laser radiation may be used for the measuring
beam, but to reduce thin film effects, broad band radiation should
be used instead or in addition.
[0057] However, in the case of level sensor, for example, using a
different wavelength for the measuring beam than for the patterned
projection beam, there will likely be a difference in the focus
detected by the level sensor passing its measuring beam through the
projection system from an actual focus associated with the
patterned projection beam passing through the same projection
system. This is because one or more projection system
characteristics (such as refractive index) vary with wavelength.
Thus, a change of refractive index somewhere in the optical path of
the measuring beam (having a certain wavelength) may cause a
detected focus to differ from an actual focus associated with the
patterned projection beam (having a different wavelength). In
addition or alternatively, other measurement results using a
measuring beam, such as alignment, could similarly be affected. For
example, in the case of an alignment beam, the actual lateral
position of the patterned projection beam on the substrate maybe
different from the expected lateral position of the patterned beam
as determined by an alignment measurement using an alignment
measuring beam projected on an alignment mark on the substrate.
[0058] A change of the refractive index in the optical path of the
measuring beam may occur in any number of ways. Examples
include:
[0059] temperature change of the liquid and/or the optical element
through which the measuring beam passes;
[0060] pressure change of the liquid and/or the optical element
through which the measuring beam passes;
[0061] composition change of the liquid (e.g., contamination);
and
[0062] pressure and/or temperature change in a flushing gas used to
condition the measuring beam path into and/or out of the projection
system.
[0063] Furthermore, a difference between a value measured using a
measuring beam and an actual value associated with a patterned
projection beam may also result from one or more other changes. For
example, a change in the wavelength of the patterned projection
beam may cause a measurement made using a measuring beam to be
inaccurate. Similarly, a change in the wavelength of the measuring
beam may cause a measurement made using that measuring beam to be
inaccurate. Furthermore, movement (manipulation) of one or more
optical elements in the projection system or substrate height
movement may cause a difference between a value measured using a
measuring beam and an actual value associated with a patterned
projection beam.
[0064] Accordingly, in an embodiment, a metrology model/method is
implemented to correct for the difference between an exposure
parameter value measured using a measuring beam and an applied
exposure parameter value associated with a patterned projection
beam attributable to the difference in wavelength of the measuring
beam and the projection beam.
[0065] FIG. 7 depicts a schematic flow chart of the metrology
method according to an embodiment of the invention.
[0066] At step 30, one or more sensors 26 measure one or more of
the physical property changes as described above at or near the
time the measuring beam measures an exposure parameter P (such as
focus, substrate height, and/or alignment). For example, a pressure
sensor may measure the pressure of the liquid, flushing gas and/or
optical element through which the measuring beam passes.
Additionally or alternatively, a temperature sensor may measure the
temperature of the liquid, flushing gas and/or optical element
through which the measuring beam passes. In an embodiment, multiple
different types of measurements may be made (e.g., pressure and
temperature measurement) and/or multiple measurements of the same
type may be made (e.g., multiple pressure measurements). The number
of measurements are designated by the symbol j. The one or more
measured physical property values may then be denominated as array
X_j. In an embodiment, one or more sensors provide a measured
physical property value as a difference with respect to a nominal
value, e.g., at which the lithographic apparatus was optimally
adjusted. For example, a temperature sensor may provide the
difference between the actual temperature measured (e.g.,
22.3.degree. C.) and a nominal temperature at which the
lithographic apparatus was optimally adjusted (e.g., 22.1.degree.
C.) as the temperature measurement (i.e., 0.2.degree. C.). In an
embodiment, it will be appreciated that the method may be extended
to situations where a nominal value (i.e., calibration) has not
been established through the use of additional calculations and/or
measurements.
[0067] At step 32, the impact of the one or more measured physical
property values X_j on the exposure parameter P is determined or
obtained. This impact maybe designated as the derivative dP/dX_j.
For example, where the exposure parameter P is focus and the
measured physical property values X_j are temperature and pressure
of the immersion liquid, dP/dX_j may represent the rate of change
of focus with respect to temperature and pressure.
[0068] In an embodiment, dP/dX_j may be determined at, before or
after step 31. In other words, dP/dX_j may be determined off-line,
i.e., before the measuring beam measures the exposure parameter P,
or on-line, i.e., at or near the time the measuring beam measures
the exposure parameter P. In an embodiment, dP/dX_j may be
determined by experiment/calibration, from empirical results,
and/or by optical theory (e.g., optical ray tracing). For example,
dP/dX_j may be calculated from the application of materials values
(such as a table of values for a particular physical property at
different conditions, e.g., the refractive index of a material at
various temperatures) to relevant physics and/or mathematical
formulas. In another example, dP/dX_j may be determined by
experimental measurement. Furthermore, dP/dX_j may be determined
for multiple exposure and/or measuring beam wavelengths and may be
a difference between the value for the exposure beam wavelength and
the measuring beam wavelength. Additionally or alternatively,
dP/dX_j maybe determined per projection system type (e.g., a
projection system used in multiple lithographic apparatus) or
individually per specific projection system in a lithographic
apparatus.
[0069] At step 34, the measured exposure parameter P is corrected
at least in part to take account of the measured physical property
values X_j. In an embodiment, this correction maybe formulated as:
P_applied=P_measured-sum(j){X.sub.--j*dP/dX.sub.--j} where
P_applied is the exposure parameter to be applied, for example,
during exposure of the substrate by a patterned projection beam and
P_measured is the exposure parameter as measured using the
measuring beam. Thus, the term "sum (j) (X_j*dP/dX_j)" is the
cumulative offset to be applied to the measured exposure parameter
to obtain an exposure parameter to be applied, for example, during
exposure of the substrate. The cumulative offset is the sum of the
respective offsets attributable to each of the measured physical
values X_j. Matrix operations may be used for the correction so as
to address possible cross terms between certain physical
properties, such as projection system manipulator and environmental
(e.g., temperature, pressure) dependencies. The determination
and/or application of the exposure parameter to be applied maybe
performed continuously or at intermittent times.
[0070] So, in an example, a level sensor may project a measuring
beam through an optical element of the projection system of a
lithographic apparatus and through an immersion liquid to measure a
height of the substrate F_measured during exposure of the
substrate, the measured height corresponding to a focus for the
patterned projection beam. This measured height (and thus focus)
may then be corrected to take account of the temperature (X_1) and
pressure (X_2) of the immersion liquid to yield a corrected height
F_applied (and thus focus) to be applied during exposure of the
substrate. A corrective function of the focus with respect to the
temperature (dF/dX_1) and pressure (dF/dX_2) is provided (e.g., by
experiment or empirical results). The corrective function is then
multiplied with the measured values of the pressure and temperature
and added together (sum(j){X_j*dF/dX_j}) to yield a cumulative
offset to be applied to the measured height to yield the corrected
height (and thus corrected focus). This may be summarized by the
formula F_applied=F_measured-sum(j){X_j*dF/dX_j}.
[0071] In another example, an alignment sensor may project a
measuring beam through an optical element of the projection system
of a lithographic apparatus and through an immersion liquid to
measure a X-Y position of the substrate LP_measured during exposure
of the substrate, the measured X-Y position corresponding to a
lateral placement of the patterned projection beam. This measured
X-Y position (and thus lateral placement) may then be corrected to
take account of the temperature (X_1) and pressure (X_2) of the
immersion liquid to yield a corrected X-Y position LP_applied (and
thus lateral placement) to be applied during exposure of the
substrate. A corrective function of the lateral placement with
respect to the temperature (dLP/dX_1) and pressure (dLP/dX_2) is
provided (e.g., by experiment or empirical results). The corrective
function is then multiplied with the measured values of the
pressure and temperature and added together (sum(j){X_j*dLP/dX_j})
to yield a cumulative offset to be applied to the measured X-Y
position to yield the corrected X-Y position (and thus corrected
lateral placement). This may be summarized by the formula
LP_applied=LP_measured-sum(j){X_j*dLP/dX_j }.
[0072] In an embodiment, the measured exposure parameter may be
specifically corrected for the wavelength of the measuring beam and
of the exposure beam to yield the exposure parameter to be applied.
For example, this may be formulated as:
P_applied=P_measured-.DELTA.(MV)*(dP/dMV(measuring beam
wavelength)-dP/dMV(exposure wavelength)) where P_applied is the
exposure parameter, such as focus or lateral placement, to be
applied, for example, during exposure of the substrate by a
patterned projection beam, P_measured is the exposure parameter as
measured using the measuring beam, .DELTA.(MV) is the difference in
the measured physical property value, such as temperature or
pressure, from a nominal value (typically a value at which the
lithographic apparatus was optimally configured), dP/dMV(measuring
beam wavelength) is the rate of change of the exposure parameter
with respect to the measured physical property value for the
measuring beam wavelength, and dP/dMV(exposure wavelength) is the
rate of change of the exposure parameter with respect to the
measured physical property value for the measuring beam
wavelength.
[0073] A lithographic apparatus may have various constants defined
to provide good or optimal performance. For example, the
lithographic apparatus may have one or more constants associated
with the projection system such as positioning of one or more
optical elements in the projection system and/or one or more
constants associated with the alignment system such as alignment
mark configuration and/or location. In embodiment, the metrology
model may be implemented to correct for the wavelength dependency
of these constants. In other words, one or measured physical
property values, such as pressure and/or temperature, may be used
in association with, for example, a rate of change of the constant
relative to the measured value or a rate of change of a relevant
exposure parameter relative to the measured value (e.g.
dalignment/dtemperature or dfocus/dpressure) to yield a corrected
constant.
[0074] To implement the method described above, a correction system
may be provided to a lithographic apparatus which is configured or
programmed to perform an embodiment of the method as described
herein. The correction system may be a computer program
incorporated into a processor or sensor of the lithographic
apparatus. Further, a computer program product (e.g., a software
program on a disk or in a memory) may be provided to perform an
embodiment of the method as described herein.
[0075] In European Patent Application No. 03257072.3, the idea of a
twin or dual stage immersion lithography apparatus is disclosed.
Such an apparatus is provided with two tables for supporting a
substrate. Leveling measurements are carried out with a table at a
first position, without immersion liquid, and exposure is carried
out with a table at a second position, where immersion liquid is
present. Alternatively, the apparatus has only one table. In a
preferred embodiment, the apparatus, method and/or computer program
product as described herein is applied to a single stage/table
lithography apparatus.
[0076] Although specific reference may be made in this text to the
use of lithographic apparatus in the manufacture of ICs, it should
be understood that the lithographic apparatus described herein may
have other applications, such as the manufacture of integrated
optical systems, guidance and detection patterns for magnetic
domain memories, flat-panel displays, liquid-crystal displays
(LCDs), thin-film magnetic heads, etc. The skilled artisan will
appreciate that, in the context of such alternative applications,
any use of the terms "wafer" or "die" herein may be considered as
synonymous with the more general terms "substrate" or "target
portion", respectively. The substrate referred to herein may be
processed, before or after exposure, in for example a track (a tool
that typically applies a layer of resist to a substrate and
develops the exposed resist), a metrology tool and/or an inspection
tool. Where applicable, the disclosure herein may be applied to
such and other substrate processing tools. Further, the substrate
may be processed more than once, for example in order to create a
multi-layer IC, so that the term substrate used herein may also
refer to a substrate that already contains multiple processed
layers.
[0077] The terms "radiation" and "beam" used herein encompass all
types of electromagnetic radiation, including ultraviolet (UV)
radiation (e.g. having a wavelength of or about 365, 248, 193, 157
or 126 nm).
[0078] The term "lens", where the context allows, may refer to any
one or combination of various types of optical components,
including refractive and reflective optical components.
[0079] While specific embodiments of the invention have been
described above, it will be appreciated that the invention may be
practiced otherwise than as described. For example, where
applicable, an embodiment of the invention may take the form of a
computer program containing one or more sequences of
machine-readable instructions describing a method as disclosed
above, or a data storage medium (e.g. semiconductor memory,
magnetic or optical disk) having such a computer program stored
therein. For example, the metrology model/method may be implemented
as a computer program and the computer program may interact with
the lithographic apparatus to obtain measured data (e.g., obtain a
measured focus from one or more level sensors of the lithographic
apparatus and/or obtain a measured lateral placement from one or
more alignment sensors of the lithographic apparatus) and return
corrected data (e.g., return the measured focus as corrected to
account for the different wavelength of the level sensor(s)
measuring beam and/or return the measured lateral placement as
corrected to account for the different wavelength of the alignment
sensor(s) measuring beam).
[0080] One or more embodiments of the invention may be applied to
any immersion lithography apparatus, in particular, but not
exclusively, those types mentioned above and whether the immersion
liquid is provided in the form of a bath or only on a localized
surface area of the substrate. A liquid supply system as
contemplated herein should be broadly construed. In certain
embodiments, it may be a mechanism or combination of structures
that provides a liquid to a space between the projection system and
the substrate and/or substrate table. It may comprise a combination
of one or more structures, one or more liquid inlets, one or more
gas inlets, one or more gas outlets, and/or one or more liquid
outlets that provide liquid to the space. In an embodiment, a
surface of the space may be a portion of the substrate and/or
substrate table, or a surface of the space may completely cover a
surface of the substrate and/or substrate table, or the space may
envelop the substrate and/or substrate table. The liquid supply
system may optionally further include one or more elements to
control the position, quantity, quality, shape, flow rate or any
other features of the liquid.
[0081] The immersion liquid used in the apparatus may have
different compositions, according to the desired properties and the
wavelength of exposure radiation used. For an exposure wavelength
of 193 nm, ultra pure water or water-based compositions may be used
and for this reason the immersion liquid is sometimes referred to
as water and water-related terms such as hydrophilic, hydrophobic,
humidity, etc. may be used.
[0082] More generally, each step of the method may be executed on
any general computer, such as a mainframe computer, personal
computer or the like and pursuant to one or more, or a part of one
or more, program modules or objects generated from any programming
language, such as C++, Java, Fortran or the like. And still
further, each step, or a file or object or the like implementing
each step, may be executed by special purpose hardware or a circuit
module designed for that purpose. For example, the invention may be
implemented as a firmware program loaded into non-volatile storage
or a software program loaded from or into a data storage medium as
machine-readable code, such code being instructions executable by
an array of logic elements such as a microprocessor or other
digital signal processing unit.
[0083] The invention may be implemented as an article of
manufacture comprising a computer usable medium having computer
readable program code means therein for executing the method steps
of the invention, a program storage device readable by a machine,
tangibly embodying a program of instructions executable by a
machine to perform the method steps of the invention, a computer
program product, or an article of manufacture comprising a computer
usable medium having computer readable program code means therein,
the computer readable program code means in said computer program
product comprising computer readable code means for causing a
computer to execute the steps of the invention. Such an article of
manufacture, program storage device, or computer program product
may include, but is not limited to, CD-ROMs, diskettes, tapes, hard
drives, computer system memory (e.g. RAM or ROM) and/or the
electronic, magnetic, optical, biological or other similar
embodiment of the program (including, but not limited to, a carrier
wave modulated, or otherwise manipulated, to convey instructions
that can be read, demodulated/decoded and executed by a computer).
Indeed, the article of manufacture, program storage device or
computer program product may include any solid or fluid
transmission medium, magnetic or optical, or the like, for storing
or transmitting signals readable by a machine for controlling the
operation of a general or special purpose computer according to the
method of the invention and/or to structure its components in
accordance with a system of the invention.
[0084] The invention may also be implemented in a system. A system
may comprise a computer that includes a processor and a memory
device and optionally, a storage device, an output device such as a
video display and/or an input device such as a keyboard or computer
mouse. Moreover, a system may comprise an interconnected network of
computers. Computers may equally be in stand-alone form (such as
the traditional desktop personal computer) or integrated into
another apparatus (such as a lithographic apparatus).
[0085] The system may be specially constructed for the required
purposes to perform, for example, the method steps of the invention
or it may comprise one or more general purpose computers as
selectively activated or reconfigured by a computer program in
accordance with the teachings herein stored in the computer(s). The
system could also be implemented in whole or in part as a
hard-wired circuit or as a circuit configuration fabricated into an
application-specific integrated circuit. The invention presented
herein is not inherently related to a particular computer system or
other apparatus. The required structure for a variety of these
systems will appear from the description given.
[0086] In the case of diagrams depicted herein, they are provided
by way of example. There may be variations to these diagrams or the
steps (or operations) described herein without departing from the
spirit of the invention. For instance, in certain cases, the steps
may be performed in differing order, or steps may be added, deleted
or modified. All of these variations are considered to comprise
part of the invention as recited in the appended claims.
[0087] The descriptions above are intended to be illustrative, not
limiting. Thus, it will be apparent to one skilled in the art that
modifications may be made to the invention as described without
departing from the scope of the claims set out below.
* * * * *