U.S. patent application number 13/022518 was filed with the patent office on 2011-09-08 for lithographic apparatus and scanning method.
This patent application is currently assigned to ASML NETHERLANDS B.V.. Invention is credited to Gerben Frank DE LANGE, Johannes Catharinus Hubertus Mulkens.
Application Number | 20110216301 13/022518 |
Document ID | / |
Family ID | 44531070 |
Filed Date | 2011-09-08 |
United States Patent
Application |
20110216301 |
Kind Code |
A1 |
DE LANGE; Gerben Frank ; et
al. |
September 8, 2011 |
LITHOGRAPHIC APPARATUS AND SCANNING METHOD
Abstract
A lithographic apparatus includes a first support to support a
first patterning device; a second support to support a second
patterning device, each of the first and the second patterning
device capable of imparting a radiation beam with a pattern in its
cross-section to form a patterned radiation beam; a substrate table
constructed to hold a substrate; a projection system to project the
patterned radiation beam onto a target portion of the substrate; a
controller to drive the first support and the second support and
arranged to: drive the first support to perform a scanning
movement; drive the second support to accelerate during at least
part of the scanning movement of the first support; and drive the
second support to perform a scanning movement upon completion of
the scanning movement of the first support, so as to scan a die
adjacent a die previously scanned during the scanning movement of
the first support.
Inventors: |
DE LANGE; Gerben Frank;
(Best, NL) ; Mulkens; Johannes Catharinus Hubertus;
(Valkenswaard, NL) |
Assignee: |
ASML NETHERLANDS B.V.
Veldhoven
NL
|
Family ID: |
44531070 |
Appl. No.: |
13/022518 |
Filed: |
February 7, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61310532 |
Mar 4, 2010 |
|
|
|
61331884 |
May 6, 2010 |
|
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Current U.S.
Class: |
355/72 ;
355/77 |
Current CPC
Class: |
G03F 7/70066 20130101;
G03F 7/70208 20130101; G03B 27/54 20130101 |
Class at
Publication: |
355/72 ;
355/77 |
International
Class: |
G03B 27/58 20060101
G03B027/58 |
Claims
1. A lithographic apparatus comprising: a first support constructed
to support a first patterning device; a second support constructed
to support a second patterning device; wherein the first patterning
device is capable of imparting a radiation beam with a pattern in
its cross section to form a first patterned radiation beam; wherein
the second patterning device is capable of imparting a radiation
beam with a pattern in its cross section to form a second patterned
radiation beam; a substrate table constructed to hold a substrate;
a projection system configured to project the first and second
patterned radiation beams next to each other onto a target portion
of the substrate; and a controller configured to drive the first
support and the second support, the controller being arranged to:
drive the first support to perform a scanning movement; drive the
second support to accelerate during at least part of the scanning
movement of the first support.
2. The lithographic apparatus of claim 1, wherein the projection
system is configured to project the first and second patterned
radiation beams adjacent to each other.
3. The lithographic apparatus of claim 1, wherein the controller is
further arranged to drive the second support to perform a scanning
movement upon completion of the scanning movement of the first
support, so as to scan a die adjacent a die previously scanned
during the scanning movement of the first support.
4. The lithographic apparatus of claim 3, wherein the controller is
further arranged to drive the substrate table at a substantially
constant substrate table scanning velocity during the scanning
movement of the first support and the scanning movement of the
second support.
5. The lithographic apparatus of claim 1, wherein the projection
system is arranged to alternately project the pattern of the
patterning device and the second patterning device onto a row or
column of adjacent dies.
6. The lithographic apparatus of claims 1, wherein the second
support is moved, during the scanning movement of the support, to a
scanning start position and velocity by: decelerating the second
support from a previous scanning movement; stopping the second
support; accelerating the second support to move back in a
direction reverse to the scanning movement; decelerating and
stopping the second support; and accelerating the second support to
the scanning speed.
7. The lithographic apparatus of claim 1, wherein the second
support is moved during the scanning movement of the first support,
to a scanning start position and velocity by: decelerating the
second support from a previous scanning movement; stopping the
second support; and accelerating the second support to the scanning
speed in reverse direction as compared to the previous scanning
movement of the second support.
8. The lithographic apparatus of claim 1, wherein the projection
system comprises: a first projection system part configured to
project a beam patterned by the first patterning device held by the
first support; a second projection system part configured to
project a beam patterned by the second patterning device held by
the second support; and a third projection system part configured
to project the patterned beam projected by the first and/or second
projection system parts onto the substrate.
9. The lithographic apparatus of claim 7, wherein the controller is
arranged to activate a first optical path via the first projection
system part during the scanning movement of the first support and
to activate a second optical path via the second projection system
part during the scanning movement of the second support.
10. The lithographic apparatus of claim 1, comprising an
illumination system comprising a first illuminator configured to
illuminate the patterning device held by the first support and a
second illuminator configured to illuminate the second patterning
device held by the second support.
11. The lithographic apparatus of claim 10, wherein the
illumination system comprises two sources of radiation
12. The lithographic apparatus of claim 1, comprising an optical
switch arranged to couple the patterned beam into a first
projection system part and/or a second projection system part of
the projection system.
13. The lithographic apparatus of claim 1, wherein the lithographic
apparatus is a dual stage lithographic apparatus comprising a
measurement part configured to perform a substrate levelling
measurement, and an exposure part, the lithographic apparatus
comprising dual levelling sensors at the measurement part.
14. The lithographic apparatus of claim 13, wherein the dual
levelling sensors comprise a coarse levelling sensor and a fine
levelling sensor.
15. The lithographic apparatus of claim 14, wherein the dual
levelling sensors are configured to each measure in parallel a part
of a surface of the substrate.
16. The lithographic apparatus of claim 1, wherein the lithographic
apparatus is a dual stage lithographic apparatus comprising a
measurement part configured to perform a substrate levelling
measurement, and an exposure part, the lithographic apparatus
comprising a levelling sensor at the measure part and a levelling
sensor at the exposure part.
17. The lithographic apparatus of claim 1, wherein, in use, the
second support accelerates during the at least part of the scanning
movement of the first support to a scanning start position and
velocity.
18. A combination of a lithographic apparatus of claim 1 and a
handler, the hander comprising a leveling sensor configured to
perform a substrate leveling measurement.
19. A lithographic scanning method for projecting patterns from a
first patterning device and a second patterning device onto a
substrate, the method comprising: performing a scanning movement by
a first support configured to hold the first patterning device;
accelerating a second support configured to hold the second
patterning device, during at least part of the scanning movement of
the first support, to a scanning start position and velocity; and
performing a scanning movement by the second support upon
completion of the scanning movement of the first support, so as to
scan a die adjacent a die previously scanned during the scanning
movement by the first support.
20. The method of claim 19, wherein, in use, the second support
accelerates during the at least part of the scanning movement of
the first support to a scanning start position and velocity.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority and benefit under 35 U.S.C.
.sctn.119(e) to U.S. Provisional Patent Application No. 61/310,532,
entitled "Lithographic Apparatus and Scanning Method", filed on
Mar. 4, 2010 and U.S. Provisional Patent Application No.
61/331,884, entitled "Lithographic Apparatus and Scanning Method",
filed on May 6, 2010. The contents of these applications are
incorporated herein in their entirety by reference.
FIELD
[0002] The present invention relates to a lithographic apparatus
and a lithographic scanning method.
BACKGROUND
[0003] 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 such a case, 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. including 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. Conventional
lithographic apparatus include so-called steppers, in which each
target portion is irradiated by exposing an entire pattern onto the
target portion at once, 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.
[0004] In order to make use of a lithographic apparatus as
efficiently as possible, it is desirable to achieve a high
throughput of the lithographic apparatus, so that a large amount of
substrates can be processed by the lithographic apparatus in a
shortest possible time.
SUMMARY
[0005] It is desirable to provide a lithographic apparatus having a
high throughput.
[0006] According to an embodiment of the invention, there is
provided a lithographic apparatus comprising: a first support
constructed to support a first patterning device; a second support
constructed to support a second patterning device; wherein the
first patterning device is capable of imparting a radiation beam
with a pattern in its cross section to form a first patterned
radiation beam; wherein the second patterning device is capable of
imparting a radiation beam with a pattern in its cross section to
form a second patterned radiation beam; a substrate table
constructed to hold a substrate; a projection system configured to
project the first and second patterned radiation beams next to each
other onto a target portion of the substrate; a controller
configured to drive the first support and the second support, the
controller being arranged to: drive the first support to perform a
scanning movement; drive the second support to accelerate during at
least part of the scanning movement of the first support.
[0007] According to an embodiment of the invention, there is
provided a lithographic scanning method for projecting patterns
from a first patterning device and a second patterning device onto
a substrate, the method including performing a scanning movement by
a first support configured to hold the first patterning device;
accelerating a second support configured to hold the second
patterning device, during at least part of the scanning movement of
the first support, to a scanning start position and velocity; and
performing a scanning movement by the second support upon
completion of the scanning movement of the first support, so as to
scan a die adjacent a die previously scanned during the scanning
movement by the first support.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] 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:
[0009] FIG. 1 depicts a lithographic apparatus in which an
embodiment of the invention may be applied;
[0010] FIGS. 2A and 2B each depict a schematic view of a
lithographic apparatus in accordance with an embodiment of the
invention;
[0011] FIGS. 3A and 3B depict a schematic top view of scanning
schemes in accordance with an embodiment of the invention; and
[0012] FIGS. 4A-4E depict successive support positions of a
schematic scanning scheme to illustrate an embodiment of the
invention.
[0013] FIG. 5a depicts an intensity of patterned radiation beams
onto a wafer.
[0014] FIG. 5b depicts an intensity of patterned radiation beams
onto a wafer.
DETAILED DESCRIPTION
[0015] FIG. 1 schematically depicts a lithographic apparatus
according to one embodiment of the invention. The apparatus
includes an illumination system (illuminator) IL configured to
condition a radiation beam B (e.g. UV radiation or any other
suitable radiation), a patterning device support or support
structure (e.g. a mask table) MT constructed to support a
patterning device (e.g. a mask) MA and connected to a first
positioning device PM configured to accurately position the
patterning device in accordance with certain parameters. The
apparatus also includes a substrate table (e.g. a wafer table) WT
or "substrate support" constructed to hold a substrate (e.g. a
resist-coated wafer) W and connected to a second positioning device
PW configured to accurately position the substrate in accordance
with certain parameters. The apparatus further includes a
projection system (e.g. a refractive projection lens system) PS
configured to project a pattern imparted to the radiation beam B by
patterning device MA onto a target portion C (e.g. including one or
more dies) of the substrate W.
[0016] 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, to direct, shape, or
control radiation.
[0017] The patterning device support 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 patterning device support can use
mechanical, vacuum, electrostatic or other clamping techniques to
hold the patterning device. The patterning device support may be a
frame or a table, for example, which may be fixed or movable as
required. The patterning device support 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."
[0018] 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 so 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.
[0019] 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.
[0020] 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".
[0021] 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).
[0022] The lithographic apparatus may be of a type having two (dual
stage) or more substrate tables or "substrate supports" (and/or two
or more mask tables or "mask supports"). In such "multiple stage"
machines the additional tables or supports may be used in parallel,
or preparatory steps may be carried out on one or more tables or
supports while one or more other tables or supports are being used
for exposure.
[0023] The lithographic apparatus may also be of a type wherein at
least a portion of the substrate may be covered by a liquid having
a relatively high refractive index, e.g. water, so as to fill a
space between the projection system and the substrate. An immersion
liquid may also be applied to other spaces in the lithographic
apparatus, for example, between the patterning device (e.g. mask)
MA and the projection system. Immersion techniques can be used to
increase the numerical aperture of projection systems. The term
"immersion" as used herein does not mean that a structure, such as
a substrate, must be submerged in liquid, but rather only means
that a liquid is located between the projection system and the
substrate during exposure.
[0024] 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 including, for example, suitable directing
minors 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.
[0025] The illuminator IL may include an adjuster AD configured to
adjust 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 include 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.
[0026] The radiation beam B is incident on the patterning device
(e.g., mask MA), which is held on the mask support structure (e.g.,
mask table MT), and is patterned by the patterning device. Having
traversed the patterning device (e.g. mask) MA, the radiation beam
B passes through the projection system PS, which focuses the beam
onto a target portion C of the substrate W. With the aid of the
second positioning device 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 B.
Similarly, the first positioning device PM and another position
sensor (which is not explicitly depicted in FIG. 1) can be used to
accurately position the patterning device (e.g. mask) MA with
respect to the path of the radiation beam B, e.g. after mechanical
retrieval from a mask library, or during a scan. In general,
movement of the patterning device support (e.g. 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 positioning device PM. Similarly, movement
of the substrate table WT or "substrate support" 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 patterning device support (e.g. mask
table) MT may be connected to a short-stroke actuator only, or may
be fixed. Patterning device (e.g. mask) MA and substrate W may be
aligned using patterning device alignment marks, 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 patterning device (e.g. mask) MA, the
patterning device alignment marks may be located between the
dies.
[0027] The depicted apparatus could be used in at least one of the
following modes:
1. In step mode, the patterning device support (e.g. mask table) MT
or "mask support" and the substrate table WT or "substrate support"
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 or
"substrate support" 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. 2. In scan mode, the
patterning device support (e.g. mask table) MT or "mask support"
and the substrate table WT or "substrate support" 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 or "substrate
support" relative to the patterning device support (e.g. mask
table) MT or "mask support" may be determined by the
(de-)magnification and image reversal characteristics of the
projection system PS. 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. 3. In another mode, the
patterning device support (e.g. mask table) MT or "mask support" is
kept essentially stationary holding a programmable patterning
device, and the substrate table WT or "substrate support" 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 "substrate support" 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.
[0028] Combinations and/or variations on the above described modes
of use or entirely different modes of use may also be employed.
[0029] As stated above, achieving a high throughput may be
considered highly desirable in the lithographic apparatus. In order
to be able to achieve such high throughput, many developments have
taken place such as for example increasing a scanning speed,
optimizing scanning sequences, increasing a effective mask size,
making use of dual mask lithography whereby two masks (patterning
devices) are projected sequentially onto the substrate, making use
of a dual stage configuration whereby leveling measurement and
exposure are performed sequentially.
[0030] In an embodiment, a gain in throughput may be achieved by
equipping the lithographic apparatus with two patterning devices
(e.g. mask) stages and two light branches, an example of which is
schematically depicted in FIG. 2A: a first light branch that
illuminates the first patterning device or reticle (mask) MA of the
first patterning or reticle stage MT into a first projection system
part PS1, and a second light branch that illuminates the second
patterning device or reticle MA2 held by second patterning device
or reticle stage MT2 into a second projection system part PS2. Both
the first and second light branch couple their image from the first
respectively second projection system part PS1, PS2 into a third
projection system part PS3 which projects the image onto the
substrate W held by substrate table WT. A coupling device CD (e.g.
comprising mirrors, switches etc may be provided between the first
and second projection system part on the one hand and the third
projection system part on the other hand.
[0031] As illustrated in FIG. 3A, in a lithographic apparatus
according to the state of the art, a scanning movement is
performed, by the patterning device or reticle stage MT and the
substrate stage WT, whereby the pattern is projected onto a die D1
of the substrate W. Then, both the patterning device or reticle
stage and the substrate stage are decelerated, stopped, accelerated
in reverse direction and brought to a new scanning position at a
desired scanning speed in opposite direction to the previous scan.
In between the scans, the substrate table is moved in the X
direction. Thereby, a meander shaped pattern of movement is
described by the reticle stage and the substrate stage. The total
time for exposing a substrate W (such as a wafer) is now formed by
a sum of the time periods during which the scanning exposures takes
place, and a sum of the time periods during which the stages are
brought to a position and speed for each following scan.
[0032] In an embodiment of the invention, this time may be reduced
considerably as the lithographic apparatus allows to irradiate a
pattern onto the substrate via one of the patterning device or
reticle stages (e.g. by scanning) while during this scanning time
the other patterning device or reticle stage is brought to a
starting position and velocity for a following exposure. Thereby,
the time required in between exposures may be reduced.
[0033] In one embodiment of the invention, two illuminators ILL1,
ILL2 (illumination optics) either having a common radiation source,
or each being provided with its own radiation source. Switching may
be required so as to alternate between the first and second
patterning devices or reticles MA, MA2, this switching may be
performed in many ways. It is for example possible that two
radiation sources are alternately operated. Alternatively, one or
more displaceable mirrors or other displaceable optical elements
may be provided in an optical path. Depending on a position of the
mirror or other optical element, the corresponding beams are
directed so as to be projected onto the substrate or not: hence a
periodic changing of the position of the mirror or other optical
element may result in a desired alternating. Such mirror or other
optical element may for example be provided upstream of the third
projection system part, so as to allow either light (i.e. a beam)
from the first projection system part of from the second projection
system part to be projected onto the substrate by the third
projection system part. Furthermore, such a mirror or other optical
element may be provided upstream of the first and second projection
system parts so as to allow or block the corresponding beam to pass
through the first and/or second projection system parts (e.g. by
blocking or allowing to pass light through the first and second
reticle.
[0034] FIG. 2B depicts a slightly more detailed schematic view of a
part of a lithographic apparatus in accordance with an embodiment
of the invention. Here, first and second illuminator optics ILL1
and ILL2 are provided, each comprising a respective reticle mask
RMA1, RMA2 and a respective pupil shaper PSR1, PSR2. The
illuminator optics provide an optical path through a respective
patterning device (e.g. reticle) MA1, MA2 held by a respective
support MT1, MT2. The patterning devices and corresponding supports
may move along scanning direction SD. The first optical path via
the first illuminator and the first patterning device proceeds via
projection system part PS1, while the second optical path via the
second illuminator and the second patterning device proceeds via
projection system part PS2. Respective mirrors MR1 and MR2 reflect
both beams, i.e. from the first and second projection system parts,
to a mirror structure MR3, which may (as schematically depicted in
FIG. 2B) comprise a mirror block or dual mirrors. The beams along
the two optical paths then proceed via the third projection system
part PS3 so as to be able to project two e.g. adjacent slits
(simultaneously and/or subsequently) onto the substrate W.
[0035] In an embodiment, there is provided a lithographic apparatus
comprising a first support and a second support. The first support
is constructed to support a first patterning device. The second
support is constructed to support a second patterning device. The
first patterning device is capable of imparting a radiation beam
with a pattern in its cross section to form a first patterned
radiation beam. The second patterning device is capable of
imparting a radiation beam with a pattern in its cross section to
form a second patterned radiation beam. The lithographic apparatus
further comprises a substrate table constructed to hold a
substrate, and a projection system. The projection system is
configured to project the first and second patterned radiation
beams next to each other onto a target portion of the substrate.
The lithographic apparatus further comprises a controller
configured to drive the first support and the second support and is
arranged to drive the first support to perform a scanning movement
and drive the second support to accelerate during at least part of
the scanning movement of the first support.
[0036] The first and second patterned radiation beams may be
adjacent to each other or there may be a distance between the two
beams. The beams may be projected on the wafer as slits. The beams
may be projected onto the same die. Alternatively, each beam may be
projected onto a separate die, wherein the dies may be adjacent to
each other.
[0037] A benefit of projecting the patterned radiation beams next
to each other, is that each of the patterned radiation beams may be
controlled independently. For example, the light or radiation
intensity, also referred to as dose, may be controlled
independently. In case both patterned radiation beams are
projection simultaneously in the same slit, the dose for each of
the beams needs to be controlled to properly project the first and
second pattern. Further, the total amount of dose needs to be
controlled to achieve a proper illumination of the
radiation-sensitive resist on the substrate. It may be difficult to
match these 3 parameters. By projecting the patterned radiation
beams next to each other, the dose of each beam may be optimized,
resulting in a better illumination of the substrate.
[0038] When projecting a patterned radiation beam onto the target,
the intensity will increase during a short amount of time, before
it reaches the desired value, see FIGS. 5a and 5b. This is, for
example, caused by a shutter member that blocks the patterned beam
from entering the projection system. It will take some time to
remove the shutter member completely from the beam path, and thus
before the full intensity of the beam reaches the target. In the
same way, the intensity will decrease a short amount of time before
it reaches zero.
[0039] FIG. 5a shows the dose (I) of an embodiment in which both
patterned radiation beams are projected in a single slit as
function of time (t). Because of the need to control both the dose
of each beam, as well as the total amount of dose through the slit,
the exposure of the second pattern (P2) starts after the first
pattern (P1) has completely finished. During the time, t.sub.d,
between the full dose of P1 and full dose of P2, a pattern may not
be projected properly.
[0040] FIG. 5b shows the dose (I) of an embodiment in which each
patterned radiation beam is projected through a separate slit. When
the first pattern P1 is still being exposed at full dose, the
exposure of the second pattern P2 may be started. This way, the
second pattern P2 is at full dose when the first pattern P1 starts
to decrease. This allows the patterns to be projected more fastly
after each other. This may allow to projected adjacent dies more
closely next to each other. Alternatively, the two patterns may be
patterned at the same time.
[0041] Alternatively, in the configuration in FIG. 2B, the mirror
structure MR3 may be replaced by a combiner, such as a polygon or
any other combiner, which may enable to project the beams of both
optical paths into a same slit. In the embodiment in accordance
with FIG. 2B, the dual slits may be in use (i.e. projecting a
respective beam) simultaneously, e.g. at a takeover where a scan of
the first patterning device or reticle MA1 ends, while a scan of
the other patterning device or reticle MA2 begins, so as to allow
an efficient and fast takeover. In that case it may be desirable to
make use of two radiation sources in order to allow the projection
of the beams along the two optical paths simultaneously. A single
radiation source may be applied, however in that case the two
patterning device or masks may only be illuminated without overlap
in time. In the alternative as described above, wherein a combiner
is used, a single radiation source may be applied instead of the
dual sources.
[0042] The different optical paths may each have a different
transmission characteristic and a different degradation over time.
Furthermore, the different radiation sources may result in
differences in optical dose. It may be desirable to control a dose
so that via the different paths and/or from the different radiation
sources, a similar dose is obtained at a substrate level. An
embodiment of a control strategy to achieve this goal is provided
by measuring a non-overlapping part of each of the optical paths
and adjusting a dose of the radiation source respectively the
radiation sources so as to compensate for the measured difference
in transmission characteristics of the non overlapping parts of the
optical paths. In the case of a single, common radiation source,
the dose of the source which alternately transmits via the first
and second optical paths, is adjusted alternately to the
transmission characteristics of the optical path that is applied at
that moment. In case of two radiation sources, the dose of each of
the radiation sources is adjusted in accordance with the
transmission characteristics of the path via which the respective
radiation source is to transmit.
[0043] Each projection element may be prone to tolerances which may
result in an error of the projection by the projection system.
Optimizing a projection, one or more controllable optical elements
may be applied, such as a mirror or lens of which a position is
controlled and driven by an actuator, such as a so called lens
manipulator. In the projection system having two optical paths,
different errors may occur in each path. In the projection system
in accordance with an embodiment of the invention, in an
embodiment, the error(s) may at least partly be corrected by an
adjustable optical element in each of the paths (e.g. in projection
system parts PS1, PS2). Thereby, the common part of the paths (e.g.
the third projection system part PS3) may be held uncorrected,
provided a sufficiently large range of correction is provided in
both paths (e.g. in projection system parts PS1, PS2). In another
embodiment, correction may be provided in each of the projection
system parts PS1, PS2 and PS3. Hence, the correction in PS1 and PS3
together allow correction of the first path, while the correction
in PS2 and PS3 together allow correction of the second path.
[0044] Substrate leveling measurement may be configured to cope
with a higher throughput. Thereto, many approaches may be followed.
Some examples will now be described for a dual stage lithographic
apparatus, i.e. a lithographic apparatus wherein exposure is
performed at an exposure side, while at the same time a leveling
measurement is performed on another substrate. Given the shorter
exposure cycle that may be achieved in accordance with an
embodiment of the invention, providing an improved leveling
measurement may be desirable. In an embodiment, dual leveling
sensors may be provided, the lithographic apparatus being
configured to measure in parallel with the two leveling sensors, so
that the surface on which the leveling measurement is to be
performed, may be measured in a shorter time period. Alternatively,
dual leveling sensors may be configured as a coarse leveling sensor
and a fine leveling sensor. Thereby, a higher measurement speed may
be achieved, which may have a favorable effect on total time
required to perform a leveling measurement. Leveling measurement
may also be performed in a handler. In an embodiment, a coarse
leveling may be performed in the handler, while the fine leveling
measurement is performed at the measure side of the lithographic
apparatus. In another embodiment of the invention, part of the
leveling (e.g. coarse leveling measurement) is performed at the
measure side of the lithographic apparatus, while part of the
leveling (e.g. the fine leveling measurement) is performed by a
corresponding level sensor at the expose side.
[0045] It will be appreciated that FIGS. 2A and 2B are to be
considered as schematic configurations intended to illustrate the
concepts described in this document. In a practical embodiment,
there may for example be a larger spacing between the first and
second supports, so as to allow them to move independently.
[0046] The lithographic apparatus is accordance with an embodiment
of the invention may be applied for a variety of scanning schemes.
As referred to above and described with reference to FIG. 3A, in a
conventional lithographic apparatus, a meander shaped scanning
pattern is usually applied, whereby the patterning device or
reticle stage MT and the substrate table WT each perform a scanning
movement in order to repetitively expose the pattern onto the
substrate. In accordance with an embodiment of the invention,
adjacent dies in a row or column are successively scanned. Thereto,
a first die D1 is scanned by the first patterning device or
reticle, a second, following die D2 by the second patterning device
or reticle, a third die D3 again by the first patterning device or
reticle, a fourth die D4 by the second patterning device or
reticle, and etc. This scanning is further explained with reference
to FIGS. 4A-4E. FIGS. 4A-4E each show a schematic view of
successive steps of a reticle scanning movement. In each of these
Figures, the first patterning device or reticle stage MT is
depicted at the left side, and the second reticle or patterning
device stage MT2 at the right side. An arrow in each of the
patterning devices or reticles indicates a direction in which the
reticle moves. In the examples, it is assumed that the scanning
direction is the y direction. Where no arrow is depicted in the
patterning device or reticle, it has stopped. In FIG. 4A, the first
patterning device or reticle is at scanning speed and starts to
perform a scan. At that moment in time, the second patterning
device or reticle has just completed a scan (as symbolically
indicated by the passing of the dotted lines). Then, in FIG. 4B,
the second patterning device or reticle has decelerated and
stopped, while the first reticle performs the scan. During the scan
of the first patterning device or reticle, the second patterning
device or reticle accelerates and moves in reverse direction (FIG.
4C), decelerates and stops (FIG. 4D), and accelerates again in
scanning direction to scanning speed (FIG. 4E). At that moment, the
scanning by the first patterning device or reticle is substantially
completed, and the light paths are changed so as to project the
pattern of the second reticle on the substrate instead of the
pattern of the first patterning device or reticle. Now, the pattern
of the second patterning device or reticle is scanned. The
substrate may move at a constant velocity during the scanning. The
process as described here may result in the successive projections
of adjacent dies as depicted in FIG. 3B. The controller which
drives the first and second support (i.e. first and second
patterning device or reticle stages) may be arranged to activate a
first optical path via the first projection system part PS1 during
the scanning movement of the patterning device or reticle stage MT
and to activate a second optical path via the second projection
system part PS2 during the scanning movement of the second support
MT2.
[0047] With the method according to an embodiment of the invention,
the same or similar benefits may be achieved as with the
lithographic apparatus. With the method according to an embodiment
of the invention, the same or similar preferred embodiments may be
provided, thereby achieving the same or similar effects as
corresponding preferred embodiments of the lithographic
apparatus.
[0048] In an embodiment of the invention, the lithographic
apparatus may also be described as: a lithographic apparatus
comprising: an illumination system configured to condition a
radiation beam; a support constructed to support a patterning
device, the patterning device being capable of imparting the
radiation beam with a pattern in its cross-section to form a
patterned radiation beam; a substrate table constructed to hold a
substrate; and a projection system configured to project the
patterned radiation beam onto a target portion of the substrate,
wherein the lithographic apparatus further comprises a second
support constructed to support a second patterning device; and a
controller to drive the support and the second support, the
controller being arranged to: drive the support to perform a
scanning movement; drive the second support to accelerate, during
at least part of the scanning movement of the support, to a
scanning start position and velocity; and drive the second support
to perform a scanning movement upon completion of the scanning
movement of the support, so as to scan an adjacent die. It will be
understood that the same embodiments, features, effects etc as
described in this document, also apply to the lithographic
apparatus as described here.
[0049] 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.
[0050] Although specific reference may have been made above to the
use of embodiments of the invention in the context of optical
lithography, it will be appreciated that the invention may be used
in other applications, for example imprint lithography, and where
the context allows, is not limited to optical lithography. In
imprint lithography a topography in a patterning device defines the
pattern created on a substrate. The topography of the patterning
device may be pressed into a layer of resist supplied to the
substrate whereupon the resist is cured by applying electromagnetic
radiation, heat, pressure or a combination thereof. The patterning
device is moved out of the resist leaving a pattern in it after the
resist is cured.
[0051] 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) and extreme ultra-violet (EUV) radiation (e.g. having a
wavelength in the range of 5-20 nm), as well as particle beams,
such as ion beams or electron beams.
[0052] The term "lens", where the context allows, may refer to any
one or combination of various types of optical components,
including refractive, reflective, magnetic, electromagnetic and
electrostatic optical components.
[0053] 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, 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.
[0054] 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.
* * * * *