U.S. patent application number 12/109048 was filed with the patent office on 2008-08-21 for system and method to align and measure alignment patterns on multiple layers.
This patent application is currently assigned to ASML Holding N.V.. Invention is credited to Walter H. Augustyn, Pankaj Raval, Lev Ryzhikov.
Application Number | 20080198363 12/109048 |
Document ID | / |
Family ID | 36567885 |
Filed Date | 2008-08-21 |
United States Patent
Application |
20080198363 |
Kind Code |
A1 |
Raval; Pankaj ; et
al. |
August 21, 2008 |
System and Method to Align and Measure Alignment Patterns on
Multiple Layers
Abstract
A system and method are used to increase alignment accuracy of
feature patterns through detection of alignment patterns on both a
surface layer and at least one below surface layers of an object. A
first frequency of light, such as visible light, is used to detect
alignment patterns on the surface layer and a second frequency of
light, such as infrared light, is used to detect patterns one layer
below the surface. For example, reflected light of a first
frequency and transmitted light of a second frequency are
co-focused onto detector after impinging on respective alignment
patterns. The co-focused light is then used to determine proper
alignment of the object for subsequent pattern features. This
substantially increases accuracy of alignment of pattern features
between layers, as compared to conventional systems.
Inventors: |
Raval; Pankaj; (Fairfield,
CT) ; Augustyn; Walter H.; (Monroe, CT) ;
Ryzhikov; Lev; (Norwalk, CT) |
Correspondence
Address: |
STERNE, KESSLER, GOLDSTEIN & FOX P.L.L.C.
1100 NEW YORK AVENUE, N.W.
WASHINGTON
DC
20005
US
|
Assignee: |
ASML Holding N.V.
Veldhoven
NL
|
Family ID: |
36567885 |
Appl. No.: |
12/109048 |
Filed: |
April 24, 2008 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11272711 |
Nov 15, 2005 |
7365848 |
|
|
12109048 |
|
|
|
|
60631991 |
Dec 1, 2004 |
|
|
|
Current U.S.
Class: |
356/51 ;
356/73 |
Current CPC
Class: |
G03F 9/7003 20130101;
G03F 9/7088 20130101; G03F 9/7065 20130101; G03F 9/7084
20130101 |
Class at
Publication: |
356/51 ;
356/73 |
International
Class: |
G01J 3/00 20060101
G01J003/00; G01N 21/00 20060101 G01N021/00 |
Claims
1. A system, comprising: an alignment system including first and
second light sources and a detector that generates a measured
signal therefrom; an object, including, a first layer including a
first alignment pattern, and a second layer including a second
alignment pattern, the second layer being below the first layer;
and a focusing system that co-focuses on the detector light from
the first and second light sources after each has impinged on the
respective the first and second alignment patterns, whereby the
object is aligned based on the measured signal and wherein the
measured signal is generated from the co-focused light from the
first and second alignment patterns.
2. The system of claim 1, wherein the focusing system comprises: an
optical system positioned between the object and the detector,
wherein the optical system performs the co-focusing the light from
the at least the first and second light sources onto the
detector.
3. The system of claim 2, wherein the focusing system further
comprises: a positioning system that receives the measured signal
from the alignment system and that moves at least one of the object
and the detector relative to the optical system based on the
measured signal, such that the light from the at least first and
second light sources are co-focused on the detector.
4. The system of claim 2, wherein the optical system comprises an
optical element including at least first, second, and third
lenses.
5. The system of claim 4, wherein: the first lens comprises R1=-64
to -65 mm, R2=-71 to -72 mm, thickness.ltoreq.1.5 to 1.6 mm,
diameter,=22.0 mm, and a glass type is SF20 (Schott); the second
lens comprises R1=-71 to -72 mm, R2=15 to 16 mm, thickness.ltoreq.1
to 2 mm, diameter=22.0 mm, and a glass type is N-PSK3(Schott); and
the third lens comprises R1=15 to 16 mm, R2=-35 to -36 mm,
thickness=10 to 11 mm, diameter=22.0 mm, and a glass type is N-PK51
(Schott).
6. The system of claim 5, wherein: the first lens comprises
R1=-64.795 mm, R2=-71.20 mm, thickness=1.518 mm, diameter,=22.0 mm,
and a glass type is SF20 (Schott); the second lens comprises
R1=-71.20 mm, R2=15.469 mm, thickness=1.5 mm, diameter=22.0 mm, and
a glass type is N-PSK3 (Schott); and the third lens comprises
R1=15.469 mm, R2=-35.382 mm, thickness.ltoreq.10.083 mm,
diameter=22.0 mm, and a glass type is N-PK51 (Schott).
7. The system of claim 2, wherein the optical system comprises an
optical element including at least first and second lenses.
8. The system of claim 7, wherein: the first lens comprises R1=-26
to -27 mm, R2=infinity, thickness.ltoreq.3 mm, diameter=12 to 13
mm, and a glass type is BK7 (Schott); the second lens comprises
R1=infinity, R2=-59 to -60 mm, thickness.ltoreq.5 mm, diameter=12
to 13 mm, and a glass type is F2 (Schott).
9. The system of claim 8, wherein: the first lens comprises
R1=-26.697 mm, R2=infinity, thickness.ltoreq.3 mm, diameter=12.7
mm, and a glass type is BK7 (Schott); the second lens comprises
R1=infinity, R2=-59.03 mm, thickness.ltoreq.5 mm, diameter=12.7 mm,
and a glass type is F2 (Schott).
10. The system of claim 1, wherein: the first light source is
configured to generate visible light that is used to detect a
position of the first alignment pattern; and the second light
source is configured to generate infrared light that is used to
detect a position of the second alignment pattern.
11. The system of claim 10, wherein: the visible light is reflected
from the first alignment pattern before being focused onto the
detector using the focusing system; and the infrared light is
transmitted through the second alignment pattern before being
focused onto the detector using the focusing system.
12. The system of claim 1, wherein: the light from the first light
source is generated from a first side of the object; and the light
from the second light source is generated from a second side of the
object, opposite the first side.
13. A method, comprising: (a) generating at least a first light
beam and a second light beam; (b) impinging the first light beam
onto a first alignment pattern on a first layer of an object; (c)
focusing the impinged first light beam onto a detector; (d)
impinging the second light beam onto a second alignment pattern on
a second layer of the object, the second layer of the object being
below the first layer of the object; (e) focusing the impinged
second light beam onto the detector; (f) generating an alignment
signal based on the detected first and second alignment patterns;
and (g) aligning the object to receive a subsequent portion of a
feature pattern based on step (f).
14. The method of claim 13, wherein the first and second light
beams are focused onto the detector substantially
simultaneously.
15. The method of claim 13, wherein first light beam is visible
light and the second light beam is infrared light.
16. The method of claim 15, wherein: the visible light beam is
reflected from the first alignment pattern before being focused
onto the detector; and the infrared light beam is transmitted
through the second alignment pattern before being focused onto the
detector.
17. The method of claim 13, wherein: the first light beam is
generated from a first side of the object; and the second light
beam is generated from a second side of the object, opposite the
first side.
18. A flat panel display formed using the method of claim 13.
19. An integrated circuit formed using the method of claim 13.
20. A system, comprising: means for generating at least a first
light beam and a second light beam; means for impinging the first
light beam onto a first alignment pattern on a first layer of an
object; means for focusing the impinged first light beam onto a
detector; means for impinging the second light beam onto a second
alignment pattern on a second layer of the object, the second layer
of the object being below the first layer of the object; means for
focusing the impinged second light beam onto the detector; means
for generating an alignment signal based on the detected first and
second alignment patterns; and means for aligning the object to
receive a subsequent portion of a feature pattern based on the
alignment signal.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. Non-Provisional
Application No. 11/272,711, filed Nov. 15, 2005, which will issue
as U.S. Pat. No. 7,365,848 on Apr. 29, 2008, which claims benefit
to U.S. Provisional Application No. 60/631,991, filed Dec. 1, 2004,
all of which are incorporated by reference herein in its
entirety.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention relates to a lithographic apparatus
and a device manufacturing method.
[0004] 2. Related Art
[0005] A lithographic apparatus is a machine that applies a desired
pattern onto a target portion of a substrate. The lithographic
apparatus can be used, for example, in the manufacture of
integrated circuits (ICs), flat panel displays, and other devices
involving fine structures. In a conventional lithographic
apparatus, a patterning means, which is alternatively referred to
as a mask or a reticle, can be used to generate a circuit pattern
corresponding to an individual layer of the IC (or other device),
and this pattern can be imaged onto a target portion (e.g.,
comprising part of one or several dies) on a substrate (e.g., a
silicon wafer or glass plate) that has a layer of
radiation-sensitive material (e.g., resist). Instead of a mask, the
patterning means can comprise an array of individually controllable
elements that generate the circuit pattern.
[0006] In general, a single substrate will contain a network of
adjacent target portions that are successively exposed. Known
lithographic apparatus include steppers, in which each target
portion is irradiated by exposing an entire pattern onto the target
portion in one go, and scanners, in which each target portion is
irradiated by scanning the pattern through the beam in a given
direction (the "scanning" direction), while synchronously scanning
the substrate parallel or anti-parallel to this direction.
[0007] As discussed above, a lithographic apparatus uses a
patterning device to pattern incoming light. A static patterning
device can include reticles or masks. A dynamic patterning device
can include an array of individually controllable elements that
generate a pattern through receipt of analog or digital
signals.
[0008] Multiple layers can be formed on each substrate, with each
layer receiving feature patterns that interconnect within that
layer and to other feature patterns in previous/subsequent layers.
However, typically only an alignment patterned formed on a top
layer of the substrate is used to determine proper alignment of
feature patterns with respect to each other. With tolerances
getting smaller, it would be desirable for alignment of subsequent
feature patterns to utilize alignment patterns on the top layer and
one or more previously formed layers.
[0009] Therefore, what is needed is a system and method that allow
for measurement or detection of alignment patterns on a top layer
and one or more previously formed layers before forming a next
feature pattern.
SUMMARY
[0010] According to one embodiment of the present invention, a
system comprises an alignment system including first and second
light sources and a detector that generates a measured signal
therefrom. The system further comprises an object, including a
first layer including a first alignment pattern, and a second layer
including a second alignment pattern, the second layer being below
the first layer. The system also included a focusing system that
co-focuses on the detector light from the first and second light
sources after each has impinged on the respective the first and
second alignment patterns. The system then aligns the object based
on the measured signal wherein the measured signal is generated
from the co-focused light from the first and second alignment
patterns.
[0011] According to one embodiment of the present invention, there
is provided a method comprising the following steps. Generating at
least a first light beam and a second light beam. Impinging the
first light beam onto a first alignment pattern on a first layer of
an object. Focusing the impinged first light beam onto a detector.
Impinging the second light beam onto a second alignment pattern on
a second layer of the object, the second layer of the object being
below the first layer of the object. Focusing the impinged second
light beam onto the detector. Generating an alignment signal based
on the detected first and second alignment patterns; and aligning
the object to receive a subsequent portion of a feature pattern
based on the alignment signal.
[0012] Further embodiments and features of the present inventions,
as well as the structure and operation of the various embodiments
of the present invention, are described in detail below with
reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES
[0013] The accompanying drawings, which are incorporated herein and
form apart of the specification, illustrate embodiments of the
present invention and, together with the description, further serve
to explain the principles of the invention and to enable a person
skilled in the pertinent art to make and use the invention.
[0014] FIG. 1 depicts a lithographic apparatus, according to one
embodiment of the invention.
[0015] FIGS. 2 and 3 show alignment systems, according to various
embodiments of the present invention.
[0016] FIGS. 4 and 5 show two optical devices that can be used in
conjunction with each other in the alignment system of FIGS. 2 and
3, according to one embodiment of the present invention.
[0017] FIG. 6A shows an optical arrangement in a lithography
system, according to one embodiment of the present invention.
[0018] FIG. 6B shows an IR portion of the optical arrangement in
FIG. 6A, according to one embodiment of the present invention.
[0019] FIG. 7 shows a flowchart depicting a method, according to
one embodiment of the present invention.
[0020] The present invention will now be described with reference
to the accompanying drawings. In the drawings, like reference
numbers may indicate identical or functionally similar
elements.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0021] Overview
[0022] Although specific reference may be made in this text to the
use of a patterning device in a lithographic system that patterns a
substrate, it should be understood that the patterning device
described herein may have other applications, such as in a
projector or a projection system to pattern an object or display
device (e.g., in a projection television system, or the like).
Therefore, the use of the lithographic system and/or substrate
throughout this description is only to describe example embodiments
of the present invention.
[0023] Embodiments of the present invention provide a system and
method that are used for alignment of feature patterns through
detection of alignment patterns on both a surface layer and at
least one below (e.g., buried) surface layers of an object. Visible
light is used to detect alignment patterns on the surface layer and
infrared light is used to detect patterns one layers below the
surface. In this example, the object is made from a material
through which infrared light is transmitted and/or reflected and
off of which visible light is reflected. For example, the object
can be made from silicon. Thus, reflected visible light and
transmitted or reflected infrared light are co-focused onto a
detector. The co-focused light is then used to determine proper
alignment of the object for subsequent pattern features. This makes
it possible to align pattern features between two layers of
alignment patterns or featured patterns when one of them is buried
deeply and cannot be aligned by conventional alignment systems.
[0024] In one example, co-focusing is meant to describe when both
the visible and infrared light has a same focal length between a
focusing system and the detector. In one example, this can be
accomplished through use of an optical system. In another example,
this can be accomplished through use of an optical system in
conjunction with a positioning system that moves either the object
and/or the detector relative (e.g., towards/away) to the optical
system.
[0025] In one example of this description, visible light is within
a range of about 540-600 nm, near infrared light is within a range
of about 650-1000 nm, and infrared light is within a wavelength of
about 1000-3500 nm, while 650-3500 are all referred to as infrared
light.
Terminology
[0026] 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, for example, the manufacture of
DNA chips, MEMS, MOEMS, integrated optical systems, guidance and
detection patterns for magnetic domain memories, flat panel
displays, thin film magnetic heads, micro and macro fluidic
devices, 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.
[0027] 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) or a metrology or 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.
[0028] The term "array of individually controllable elements" as
here employed should be broadly interpreted as referring to any
device that can be used to endow an incoming radiation beam with a
patterned cross-section, so that a desired pattern can be created
in a target portion of the substrate. The terms "light valve" and
"Spatial Light Modulator" (SLM) can also be used in this context.
Examples of such patterning devices are discussed above and
below.
[0029] A programmable mirror array may comprise a
matrix-addressable surface having a viscoelastic (i.e., a surface
having appreciable and conjoint viscous and elastic properties)
control layer and a reflective surface. The basic principle behind
such an apparatus is that, for example, addressed areas of the
reflective surface reflect incident light as diffracted light,
whereas unaddressed areas reflect incident light as undiffracted
light. The addressing can be binary or through multiple
intermittent angles. Using an appropriate spatial filter, the
undiffracted light can be filtered out of the reflected beam,
leaving only the diffracted light to reach the substrate. In this
manner, the beam becomes patterned according to the addressing
pattern of the matrix-addressable surface.
[0030] It will be appreciated that, as an alternative, the filter
may filter out the diffracted light, leaving the undiffracted light
to reach the substrate. An array of diffractive optical micro
electrical mechanical system (MEMS) devices can also be used in a
corresponding manner. Each diffractive optical MEMS device can
include a plurality of reflective ribbons that can be deformed
relative to one another to form a grating that reflects incident
light as diffracted light. This is sometimes referred to as a
grating light valve.
[0031] A further alternative embodiment can include a programmable
mirror array employing a matrix arrangement of tiny mirrors, each
of which can be individually tilted about an axis by applying a
suitable localized electric field, or by employing piezoelectric
actuation means. Once again, the mirrors are matrix-addressable,
such that addressed mirrors will reflect an incoming radiation beam
in a different direction to unaddressed mirrors; in this manner,
the reflected beam is patterned according to the addressing pattern
of the matrix-addressable mirrors. The required matrix addressing
can be performed using suitable electronic means. In one example,
groups of the mirrors can be coordinated together to be addresses
as a single "pixel." In this example, an optical element in an
illumination system can form beams of light, such that each beam
falls on a respective group of mirrors.
[0032] In both of the situations described here above, the array of
individually controllable elements can comprise one or more
programmable mirror arrays.
[0033] A programmable LCD array can also be used.
[0034] It should be appreciated that where pre-biasing of features,
optical proximity correction features, phase variation techniques
and multiple exposure techniques are used, for example, the pattern
"displayed" on the array of individually controllable elements may
differ substantially from the pattern eventually transferred to a
layer of or on the substrate. Similarly, the pattern eventually
generated on the substrate may not correspond to the pattern formed
at any one instant on the array of individually controllable
elements. This may be the case in an arrangement in which the
eventual pattern formed on each part of the substrate is built up
over a given period of time or a given number of exposures during
which the pattern on the array of individually controllable
elements and/or the relative position of the substrate changes.
[0035] The terms "radiation" and "beam" used herein encompass all
types of electromagnetic radiation, including ultraviolet (UV)
radiation (e.g., having a wavelength of 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.
[0036] In the lithography environment, the term "projection system"
used herein should be broadly interpreted as encompassing various
types of projection systems, including refractive optical systems,
reflective optical systems, and catadioptric optical systems, as
appropriate, for example, for the exposure radiation being used, or
for other factors such as the use of an immersion fluid or the use
of a vacuum. Any use of the term "lens" herein may be considered as
synonymous with the more general term "projection system."
[0037] The illumination system may also encompass various types of
optical components, including refractive, reflective, and
catadioptric optical components for directing, shaping, or
controlling the beam of radiation, and such components may also be
referred to below, collectively or singularly, as a "lens."
[0038] The lithographic apparatus may be of a type having two
(e.g., 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] The lithographic apparatus may also be of a type wherein the
substrate is immersed 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. Immersion
liquids may also be applied to other spaces in the lithographic
apparatus, for example, between the patterning device and the first
element of the projection system. Immersion techniques are well
known in the art for increasing the numerical aperture of
projection systems.
[0040] Further, the apparatus may be provided with a fluid
processing cell to allow interactions between a fluid and
irradiated parts of the substrate (e.g., to selectively attach
chemicals to the substrate or to selectively modify the surface
structure of the substrate).
Exemplary Environment for a Patterning Device
[0041] Although the patterning device of the present invention can
be used in many different environments, as discussed above, a
lithographic environment will be used in the description below.
This is for illustrative purposes only.
[0042] A lithographic apparatus is a machine that applies a desired
pattern onto a target portion of an object. The lithographic
apparatus can be used, for example, to pattern an object in a
biotechnology environment, in the manufacture of ICs, flat panel
displays, micro or nano fluidic devices, and other devices
involving fine structures. In an IC-based lithographic environment,
the patterning device is used to generate a circuit pattern
corresponding to an individual layer of the IC (or other device),
and this pattern can be imaged onto a target portion (e.g.,
comprising part of one or several dies) on a substrate (e.g., a
silicon wafer or glass plate) that has a layer of
radiation-sensitive material (e.g., resist). As discussed above,
instead of a mask, in maskless IC lithography the patterning device
may comprise an array of individually controllable elements that
generate the circuit pattern.
[0043] In general, a single substrate will contain a network of
adjacent target portions that are successively exposed. Known
lithographic apparatus include steppers, in which each target
portion is irradiated by exposing an entire pattern onto the target
portion in one go, and scanners, in which each target portion is
irradiated by scanning the pattern through the beam in a given
direction (the "scanning" direction), while synchronously scanning
the substrate parallel or anti-parallel to this direction. These
concepts will be discussed in more detail below.
[0044] FIG. 1 schematically depicts a lithographic projection
apparatus 100, according to one embodiment of the invention.
Apparatus 100 includes at least a radiation system 102, a
patterning device 104 (e.g., a static device or an array of
individually controllable elements), an object table 106 (e.g., a
substrate table), and a projection system ("lens") 108.
[0045] Radiation system 102 is used to supply a beam 110 of
radiation, which in this example also comprises a radiation source
112.
[0046] Array of individually controllable elements 104 (e.g., a
programmable mirror array) is used to pattern beam 110. In one
example, the position of the array of individually controllable
elements 104 is fixed relative to projection system 108. However,
in another example, array of individually controllable elements 104
is connected to a positioning device (not shown) that positions it
with respect to projection system 108. In the example shown, each
element in the array of individually controllable elements 104 are
of a reflective type (e.g., have a reflective array of individually
controllable elements).
[0047] Object table 106 is provided with an object holder (not
specifically shown) for holding an object 114 (e.g., a resist
coated silicon wafer, a glass substrate, or the like). In one
example, substrate table 106 is connected to a positioning device
116 for accurately positioning substrate 114 with respect to
projection system 108.
[0048] Projection system 108 (e.g., a quartz and/or CaF2 lens
system or a catadioptric system comprising lens elements made from
such materials, or a mirror system) is used to project the
patterned beam received from a beam splitter 118 onto a target
portion 120 (e.g., one or more dies) of substrate 114. Projection
system 108 can project an image of the array of individually
controllable elements 104 onto substrate 114. Alternatively,
projection system 108 can project images of secondary sources for
which the elements of the array of individually controllable
elements 104 act as shutters. Projection system 108 can also
comprise a micro lens array (MLA) to form the secondary sources and
to project microspots onto substrate 114.
[0049] Source 112 (e.g., an excimer laser, or the like) produces a
beam of radiation 122. Beam 122 is fed into an illumination system
(illuminator) 124, either directly or after having traversed
conditioning device 126, such as a beam expander 126, for example.
Illuminator 124 can comprise an adjusting device 128 that sets the
outer and/or inner radial extent (commonly referred to as
.sigma.-outer and .sigma.-inner, respectively) of the intensity
distribution in beam 122. In addition, illuminator 124 can include
various other components, such as an integrator 130 and a condenser
132. In this way, beam 110 impinging on the array of individually
controllable elements 104 has a desired uniformity and intensity
distribution in its cross-section.
[0050] In one example, source 112 is within the housing of
lithographic projection apparatus 100 (as is often the case when
source 112 is a mercury lamp, for example). In another example,
source 112 is remotely located with respect to lithographic
projection apparatus 100. In this latter example, radiation beam
122 is directed into apparatus 100 (e.g., with the aid of suitable
directing mirrors (not shown). This latter scenario is often the
case when source 112 is an excimer laser. It is to be appreciated
that both of these scenarios are contemplated within the scope of
the present invention.
[0051] Beam 110 subsequently interacts with the array of
individually controllable elements 104 after being directed using
beam splitter 118. In the example shown, having been reflected by
the array of individually controllable elements 104, beam 110
passes through projection system 108, which focuses beam 110 onto a
target portion 120 of substrate 114.
[0052] With the aid of positioning device 116, and optionally
interferometric measuring device 134 on abase plate 136 that
receives interferometric beams 138 via beam splitter 140, substrate
table 106 is moved accurately, so as to position different target
portions 120 in a path of beam 110.
[0053] In one example, a positioning device (not shown) for the
array of individually controllable elements 104 can be used to
accurately correct the position of the array of individually
controllable elements 104 with respect to the path of beam 110,
e.g., during a scan.
[0054] In one example, movement of substrate table 106 is realized
with the aid of a long-stroke module (course positioning) and a
short-stroke module (fine positioning), which are not explicitly
depicted in FIG. 1. A similar system can also be used to position
the array of individually controllable elements 104. It will be
appreciated that beam 110 may alternatively/additionally be
moveable, while substrate table 106 and/or the array of
individually controllable elements 104 may have a fixed position to
provide the required relative movement.
[0055] In another example, substrate table 106 may be fixed, with
substrate 114 being moveable over substrate table 106. Where this
is done, substrate table 106 is provided with a multitude of
openings on a flat uppermost surface. A gas is fed through the
openings to provide a gas cushion, which supports substrate 114.
This is referred to as an air bearing arrangement. Substrate 114 is
moved over substrate table 106 using one or more actuators (not
shown), which accurately position substrate 114 with respect to the
path of beam 110. In another example, substrate 114 is moved over
substrate table 106 by selectively starting and stopping the
passage of gas through the openings.
[0056] Although lithography apparatus 100 according to the
invention is herein described as being for exposing a resist on a
substrate, it will be appreciated that the invention is not limited
to this use and apparatus 100 maybe used to project a patterned
beam 110 for use in resistless lithography, and for other
applications.
[0057] The depicted apparatus 100 can be used in at least one of
four modes: [0058] 1. Step mode: the entire pattern on the array of
individually controllable elements 104 is projected during a single
exposure (i.e., a single "flash") onto a target portion 120.
Substrate table 106 is then moved in the x and/or y directions to a
different position for a different target portion 120 to be
irradiated by patterned beam 110. [0059] 2. Scan mode: essentially
the same as step mode, except that a given target portion 120 is
not exposed in a single "flash." Instead, the array of individually
controllable elements 104 moves in a given direction (e.g., a "scan
direction," for example, the y direction) with a speed v, so that
patterned beam 110 is caused to scan over the array of individually
controllable elements 104. Concurrently, substrate table 106 is
simultaneously moved in the same or opposite direction at a speed
V=Mv, in which M is the magnification of projection system 108. In
this manner, a relatively large target portion 120 can be exposed,
without having to compromise on resolution. [0060] 3. Pulse mode:
the array of individually controllable elements 104 is kept
essentially stationary, and the entire pattern is projected onto a
target portion 120 of substrate 114 using pulsed radiation system
102. Substrate table 106 is moved with an essentially constant
speed, such that patterned beam 110 scans a line across substrate
106. The pattern on the array of individually controllable elements
104 is updated as required between pulses of radiation system 102,
and the pulses are timed such that successive target portions 120
are exposed at the required locations on substrate 114.
Consequently, patterned beam 110 can scan across substrate 114 to
expose the complete pattern for a strip of substrate 114. The
process is repeated until complete substrate 114 has been exposed
line by line. [0061] 4. Continuous scan mode: essentially the same
as pulse mode except that a substantially constant radiation system
102 is used and the pattern on the array of individually
controllable elements 104 is updated as patterned beam 110 scans
across substrate 114 and exposes it.
[0062] Combinations and/or variations on the above described modes
of use or entirely different modes of use may also be employed.
Exemplary Alignment System
[0063] FIGS. 2 and 3 show alignment and focusing portions 250 and
350, according to various embodiments of the present invention.
Alignment and focusing portions 250 or 350 can be used additionally
or alternatively to those portions discussed above as performing
similar operations in lithography tool 100. Through use of these
portions 250 or 350, both surface layer and intermediate layer
(e.g., up to about 150 .mu.m deep) alignment patterns can be
detected and utilized in aligning an object for subsequent feature
pattern formation, as is discussed in more detail below. In one
example, the object comprises material that allows infrared light
to be transmitted and visible light to be reflected. For example,
the object can be made from a silicon material, such as a
semiconductor wafer, a flat panel display substrate, or any
material that allows transmission of IR light.
[0064] Alignment and focusing portion 250 comprises alignment
system 252 and focusing system 254. Focusing system 254 is coupled
to an object 214 and alignment system 252. In one embodiment,
focusing system 254 includes an optical system 256. In another
embodiment, focusing system 254 includes optical system 256 and a
positioning system 258. In this latter embodiment, positioning
system 258 is coupled to one or both of object 214 and alignment
system 252 to move one or both relative to optical system 256,
i.e., towards or away from optical system 256. This is done to
allow for fine tuning of co-focusing of visible and infrared light,
as discussed in more detail below.
[0065] In one example, object 214 includes a support layer 260 and
one or more layers 262 (e.g., surface and intermediate layers),
which include areas for alignment patterns 264 and feature patterns
266. In another example, alignment patterns can be located on a
back surface of object 214.
[0066] Turning now to FIG. 3, alignment system 252 in alignment and
focusing portion 350 includes one or more light sources 370 (e.g.
for visible light detection), one or more light sources 372 (e.g.,
for IR light detection), and one or more detectors 374. Each
detector detects both visible and infrared light. For example,
detectors 374 can be one or more cameras, CCD sensors, CMOS
sensors, or the like. It is to be appreciated a number of light
sources 370/372 and detectors 374 can correlate, or a single
detector 374 and multiple light sources 370/372, or vice versa, can
be used. Also, as stated above, the light source can either be
placed in front of or behind the object 214 to allow for either
transmitted or reflected IR light. All permutations and variations
are contemplated within the scope of the present invention.
[0067] In the example shown in FIG. 3, object 214 includes a
surface layer 262A and an intermediate layer 262B. Each layer 262A
and 262B includes one or more respective alignment patterns 264A
and 264B and respective feature patterns 266A and 266B.
[0068] In one example, visible light 376 from one or more visible
light sources 370 is reflected from one or more alignment patterns
264A on surface layer 262A and infrared light 378 from one or more
infrared light sources 372 is transmitted through one or more
alignment patterns 264B on intermediate layer 262B or alignment
pattern 264B on backside of object 214. Optical system 256
co-focuses the reflected visible light 376 and the transmitted
infrared light 378 onto a respective detector 374. Each respective
detector 374 generates a measured signal from the detected visible
light 376 and infrared light 378. The measured signal generated by
detectors 374 are used to align object 214 for subsequent feature
pattern formation.
[0069] In one example, positioning system 258 is used to allow for
co-focusing or further adjust or fine adjust a focal position or
focal length between optical system 256 and detector 374 of visible
light 376 and/or infrared light 378, such that both wavelengths of
light are co-focused onto detector 374 within a desired
tolerance.
[0070] Thus, in alignment and focusing portion 350, both alignment
patterns 264A and 264B are used in order to determine feature
pattern positions on both of layers 262A and 262B. This
dual-detection operation increases alignment accuracy compared to
only being able to detect an alignment pattern on a surface layer
of an object in conventional devices.
[0071] One exemplary environment for one or more embodiments of the
present invention is in a Micralign lithography tool manufactured
by ASML of Veldhoven, The Netherlands. Example aspects of the
Micralign lithography tool can be found in U.S. Pat. Nos.
4,068,947, 4,650,315, 4,711,535, and 4,747,678, which are all
incorporated by reference herein in their entireties.
[0072] FIGS. 4 and 5 show two optical devices 456 and 556 that can
be used in conjunction with each other in optical system 256,
according to one embodiment of the present invention.
[0073] With reference to FIG. 4, optical device 456 includes first,
second, and third lenses 480, 482, and 484. The triplet lens design
provides an optical prescription that allows focusing of visible
and IR wavelengths onto a same plane together.
[0074] In one example, lenses 480, 482, and 484 have the following
characteristics, whose parameters can actually be more or less than
shown depending on desired tolerances: [0075] First lens 480
comprises R1=-64 to -65 mm, R2=-71 to -72 mm, thickness.ltoreq.1.5
to 1.6 mm, diameter, =22.0 mm, and a glass type is SF10 (Schott);
[0076] Second lens 482 comprises R1=-71 to -72 mm, R2=15 to 16 mm,
thickness.ltoreq.1 to 2 mm, diameter=22.0 mm, and a glass type is
N-PSK3 (Schott); and [0077] Third lens 484 comprises R1=15 to 16
mm, R2=-35 to -36 mm, thickness.ltoreq.10 to 11 mm, diameter=22.0
mm, and a glass type is N-PK51 (Schott).
[0078] In another example, lenses 480, 482, and 484 have the
following characteristics, whose parameters can actually be more or
less than shown depending on desired tolerances: [0079] First Lens
480: R1=-64.795 mm, R2=-71.20 mm, thickness.ltoreq.1.518 mm,
diameter, =22.0 mm. Glass type is SF20 (Schott) [0080] Second Lens
482: R1=-71.20 mm, R2=15.469 mm, thickness.ltoreq.1.5 mm.,
diameter=22.0 mm. Glass type is N-PSK3(Schott) [0081] Third Lens
484: R1=15.469 mm, R2=-35.382 mm, thickness.ltoreq.10.083 mm,
diameter=22.0 mm Glass type is N-PK51 (Schott)
[0082] With reference to FIG. 5, optical device 556 includes first
and second lenses 586 and 588. The doublet lens design provides an
optical prescription that allows focusing of visible and IR
wavelengths onto a same plane together.
[0083] In one example, lenses 586 and 588 have the following
characteristics, whose parameters can actually be more or less than
shown depending on desired tolerances: [0084] First lens 586
comprises R1=-26 to -27 mm, R2=infinity, thickness.ltoreq.3 mm,
diameter=12 to 13 mm, and a glass type is BK7 (Schott); [0085]
Second lens 588 comprises R1=infinity, R2=-59 to -60 mm,
thickness.ltoreq.5 mm, diameter=12 to 13 mm, and a glass type is F2
(Schott).
[0086] In another example, lenses 586 and 588 have the following
characteristics, whose parameters can actually be more or less than
shown depending on desired tolerances:
[0087] First Lens 586: R1=-26.697 mm, R2=infinity,
thickness.ltoreq.3 mm, diameter=12.7 mm Glass type is BK7 (Schott)
[0088] Second Lens 588: R1=infinity, R2=-59.03 mm,
thickness.ltoreq.5 mm, diameter=12.7 mm. Glass type is F2
(Schott).
Exemplary Optical Path
[0089] FIG. 6A shows an optical arrangement 680 in a lithography
system, according to one embodiment of the present invention. For
example optical arrangement 680 can be found in system 100. FIG. 6B
shows an optical system 682 of arrangement 680, according to one
embodiment of the present invention.
[0090] With reference to FIG. 6A and with respect to visible light,
visible light from a broadband light source 672 is directed to
alignment marks 664 on a substrate 614. Light reflecting from
alignment marks 664 is directed onto a detector 674 using an optic
686, for example a folding mirror or the like. Additionally or
alternatively, another optic 556 can be placed between optic 686
and detector 674, for example a Barlow optic.
[0091] With reference to FIG. 6A and with respect to IR light, IR
light from a light source 672 is directed (e.g., via a filter)
through optical system 682, e.g., an IR optical system, via a
waveguide or fiber optic device 688. The IR light directed from
optical system 682 is reflected from alignment marks 664 and
received back at optical system 682. The received reflected IR
light is directed from optical system 682 through objective lenses
680 and F-stop/aperture 692 onto folding mirror 694. In some
examples, multiple folding mirrors 694 can be used. Once reflected
from folding mirror 694, IR light is received at a field splitting
optic 696, e.g., a field splitting prism. From field splitting
prism 696, the IR light travels via a reflecting optical device 698
and an optics system 456, which includes first and second lenses of
different magnifying powers to reflecting optic 686. Depending on
magnification need, light may travel through only one of the
lenses. Then the light travels to reflecting optic 686. From
reflecting optic 686, IR light is directed onto detector 674, in
one example through optic 687.
[0092] With reference now to FIG. 6B, an exemplary arrangement of
optical system 682 is shown. In this example, optical system 682
includes a beam splitter 683, a blocking device 685, an annular
mirror 687, and a focusing optic 689, e.g. a focusing lens.
Blocking device 685 has a transparent peripheral portion 685A and
an opaque central portion 685B, at least with respect to IR light.
IR light received from optical waveguide 688 is reflected from beam
splitter 683 through transparent portion 685A of blocking device
685 to be reflected from annular mirror 687. After reflection, the
IR light is transmitted back through transparent portion 685A of
blocking device 685 and beam splitter 683 before being focused onto
alignment areas 664 on substrate 614. After reflecting from
alignment areas 664, the IR light is reflected from beam splitter
683 to travel as discussed above from optical system 682 to
detector 674.
Exemplary Operation
[0093] FIG. 7 shows a flowchart depicting a method 700, according
to one embodiment of the present invention. In one example, method
700 is carried out using one or more of the devices and/or systems
described above. In step 702, at least visible light and infrared
light are generated. In step 704, the visible light is reflected
from a first alignment pattern on a surface layer of an object. In
step 706, the reflected visible light is focused onto a detector.
In step 708, the infrared light is transmitted through a second
alignment pattern on a second layer of the object, the second layer
of the object being below the first layer of the object. In step
710, the transmitted infrared light is focused onto the detector.
In step 712, an alignment signal is generated based on the detected
first and second alignment patterns. In step 714, the object is
aligned to receive a subsequent section of a feature pattern based
on the generated alignment signal.
Exemplary Measured Alignment Patterns
[0094] Thus, according to one or more embodiments and/or examples
of the present invention, discussed above, embedded wafer targets
in IR or NIR (Near Infra Red) (hereinafter, NIR) and aligning mask
targets in visible light spectrum are detectable substantially
simultaneously or individually using one camera. In some examples,
this can be done with two separate cameras. However, in this
example additional optical components would be needed.
[0095] In a first example, this was accomplished by changing
optical characteristics of specific optical element in the view
path (e.g., element 456) in terms of its radii. This allows viewing
of the target image in visible and near IR wavelength at the same
focal position or within the available depth of focus.
[0096] In a second example, this can be achieved if a chuck that
carries a substrate can be moved in a Z-direction. The focal
position of the embedded alignment target is brought into a focal
plane of the camera in IR first. This captures the image position
information, which can be stored in memory, as would become
apparent to one of ordinary skill in the art upon reading and
understanding this invention. Then, the system retracts the chuck
to its normal position, so that the aligning mask image (projected
on top of the substrate plane) comes into the focal position of the
camera, which X-Y location can be stored in memory. In a subsequent
step, a fine alignment system can determine the offset between
these two recorded image positions and determine necessary commands
for alignment. This would substantially eliminate optical
modifications in the viewing optics. However, it can require a
control system of the machine that controls chuck movement in a
z-direction to be modified.
[0097] While this second example allows IR alignment without any
optical design changes, it can require additional parameters to be
taken into consideration. First, the complete alignment sequence
requires two distinct steps for collecting substrate and pattern
generator target pattern position data. Thus, by moving the chuck
twice for each substrate, an overall alignment time for alignment
will be considerably larger then needed for the first example.
Since the substrate is mounted on chuck that is set in best
lithographic focus (in x, y and z direction) every time it is moved
from that position, it is important to ensure that this best focus
position is maintained or repeated for optimum lithographic
performance.
[0098] In a third example, a same two step functionality can be
achieved by moving a camera in the z-direction under electronically
controlled motion. Then, at one time it will have an embedded
substrate target in IR in focus with IR wavelength and the aligning
pattern generator target in focus with a visual wavelength for
alignment. This example takes away the focus repeatability
limitations in the second example, but requires more time per wafer
for alignment.
Conclusion
[0099] While various embodiments of the present invention have been
described above, it should be understood that they have been
presented by way of example only, and not limitation. It will be
apparent to persons skilled in the relevant art that various
changes in form and detail can be made therein without departing
from the spirit and scope of the invention. Thus, the breadth and
scope of the present invention should not be limited by any of the
above-described exemplary embodiments, but should be defined only
in accordance with the following claims and their equivalents.
[0100] It is to be appreciated that only the Detailed Description
section is meant to be used in interpreting claim limitations, and
the Summary and Abstract sections are not to be used when
interpreting the claim limitations. The Summary and Abstract
sections are merely one or more exemplary embodiments or/examples
of the present invention, while the Detailed Description provides
additional/alternative embodiments and/or examples.
* * * * *