U.S. patent application number 11/685646 was filed with the patent office on 2007-07-12 for source multiplexing in lithography.
This patent application is currently assigned to Intel Corporation, a Delaware corporation. Invention is credited to Michael Goldstein, Peter J. Silverman.
Application Number | 20070159611 11/685646 |
Document ID | / |
Family ID | 32681547 |
Filed Date | 2007-07-12 |
United States Patent
Application |
20070159611 |
Kind Code |
A1 |
Goldstein; Michael ; et
al. |
July 12, 2007 |
Source Multiplexing in Lithography
Abstract
An illumination system for an extreme ultraviolet (EUV)
lithography system may include multiple sources of EUV light. The
system may combine the light from the multiple sources when
illuminating a mask.
Inventors: |
Goldstein; Michael;
(Ridgefield, CT) ; Silverman; Peter J.; (Palo
Alto, CA) |
Correspondence
Address: |
FISH & RICHARDSON, PC
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Assignee: |
Intel Corporation, a Delaware
corporation
|
Family ID: |
32681547 |
Appl. No.: |
11/685646 |
Filed: |
March 13, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10339789 |
Jan 8, 2003 |
7002164 |
|
|
11685646 |
Mar 13, 2007 |
|
|
|
Current U.S.
Class: |
355/53 |
Current CPC
Class: |
G03F 7/7005 20130101;
G03F 7/201 20130101 |
Class at
Publication: |
355/053 |
International
Class: |
G03B 27/42 20060101
G03B027/42 |
Claims
1. A method comprising: generating electromagnetic radiation that
is suitable for lithography at a first source; generating
electromagnetic radiation that is suitable for lithography at a
second source; dividing the electromagnetic radiation generated by
the first source into a first collection of beams; dividing the
electromagnetic radiation generated by the second source into a
second collection of beams; directing the electromagnetic radiation
in the beams of the first collection to a position in a lithography
system, with electromagnetic radiation in the beams of the first
collection arriving at the position with a first collection of
incidence angles; and directing the electromagnetic radiation in
the beams of the second collection to the position in the
lithography system, with electromagnetic radiation in the beams of
the second collection arriving at the position with a second
collection of incidence angles, wherein incidence angles of
electromagnetic radiation in the first collection of beams are
interleaved with incidence angles of electromagnetic radiation in
the second collection of beams.
2. The method of claim 1, wherein the incidence angles of
electromagnetic radiation in the first collection of beams are
interleaved with the incidence angles of electromagnetic radiation
in the second collection of beams so that variations in the
generation of electromagnetic radiation by either the first source
or the second source do not substantially change the net weighted
incidence angle of electromagnetic radiation at the position.
3. The method of claim 1, wherein: dividing the electromagnetic
radiation generated by the first source comprises collecting the
electromagnetic radiation generated by the first source using a
first collection of spaced apart collector optical elements; and
dividing the electromagnetic radiation generated by the second
source comprises collecting the electromagnetic radiation generated
by the second source using a second collection of spaced apart
collector optical elements.
4. The method of claim 3, wherein at least some of the collector
optical elements in the first collection are interspersed amongst
the collector optical elements in the second collection.
5. The method of claim 4, wherein at least some of the collector
optical elements in the first collection are interspersed
vertically and horizontally amongst the collector optical elements
in the second collection.
6. The method of claim 3, wherein the collector optical elements in
the first collection and the second collection comprise hexagonal
reflectors.
7. The method of claim 3, wherein the position is at a pupil in the
lithography system.
8. A system comprising: a first source of electromagnetic radiation
that is suitable for lithography; a second source of
electromagnetic radiation that is suitable for lithography; a first
collection of spaced apart collector optical elements associated
with the first source; a second collection of spaced apart
collector optical elements associated with the second source,
wherein at least some of the collector optical elements in the
first collection are interspersed amongst the collector optical
elements in the second collection; and imaging optics arranged to
direct electromagnetic radiation collected from the first source
and electromagnetic radiation collected from the second source to
the same substrate.
9. The system of claim 8, wherein the system is to direct
electromagnetic radiation collected from the first source and
electromagnetic radiation collected from the second source to a
position such that angles of incidence of the electromagnetic
radiation collected from the first source at the position are
interleaved with angles of incidence of the electromagnetic
radiation collected from the second source at the same
position.
10. The system of claim 8, wherein: the first source is positioned
at foci of the first collection of collector optical elements; and
the second source is positioned at foci of the second collection of
collector optical elements.
11. The system of claim 8, wherein the collector optical elements
in the first collection are interspersed vertically and
horizontally amongst the collector optical elements in the second
collection.
12. The system of claim 8, wherein the collector optical elements
in the first collection and the second collection comprise
tessellate reflector surfaces.
13. The system of claim 12, wherein the tessellate reflector
surfaces comprise hexagonal reflector surfaces.
14. The system of claim 12, wherein the tessellate reflector
surfaces are arranged adjacent one another.
15. A method comprising: generating electromagnetic radiation that
is suitable for lithography at a first source; generating
electromagnetic radiation that is suitable for lithography at a
second source; directing the electromagnetic radiation from the
first source to a first location; directing the electromagnetic
radiation from the second source to a second location, wherein the
first location is different from the second location; and moving a
patterned reticle relative to the first location and the second
location so that different parts of the pattern on the reticle pass
through the first location and the second location in succession to
expose a position on the substrate that integrates the energy from
the first source and from the second source.
16. The method of claim 15, further comprising patterning a
integrated circuit pattern on a substrate in accordance with a
pattern on the patterned reticle.
17. The method of claim 15, wherein moving the patterned reticle
relative to the first location and the second location comprises
scanning the patterned reticle across the first location and the
second location.
18. The method of claim 17, further comprising patterning a
substrate by scanning the substrate while scanning the patterned
reticle.
19. The method of claim 15, wherein: directing the electromagnetic
radiation from the first source comprises directing the
electromagnetic radiation to a first rectangular region; and
directing the electromagnetic radiation from the second source
comprises directing the electromagnetic radiation to a second
rectangular region.
20. The method of claim 15, wherein the first location is adjacent
to the second location.
21. The method of claim 20, wherein: moving the patterned reticle
relative to the first location and the second location comprises
scanning the patterned reticle relative to the first location and
the second location in a first direction; and the first location is
adjacent to the second location in the first direction.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of and claims
priority to U.S. patent application Ser. No. 10/339,789, filed Jan.
8, 2003 and issued on Feb. 21, 2006 as U.S. Pat. No. 7,002,164, to
U.S. patent application Ser. No. 11/196,191, filed Aug. 2, 2005,
and to U.S. application Ser. No. 11/196,231, filed Aug. 2, 2005,
the contents of all of which are incorporated herein by
reference.
BACKGROUND
[0002] The progressive reduction in feature size in integrated
circuits (ICs) is driven in part by advances in lithography. ICs
may be created by alternately etching material away from a chip and
depositing material on the chip. Each layer of materials etched
from the chip may be defined by a lithographic process in which
light shines through or reflected from a mask, exposing a
photosensitive material, e.g., a photoresist after imaging through
projection optics.
[0003] The ability to focus the light used in lithography, and
hence to produce increasingly smaller line widths in ICs, is a
function of the wavelength of the light used. Current techniques
may use light having a wavelength of about 193 nm. The use of
"soft" x-rays (wavelength range of .lamda..apprxeq.10 nm to 20 nm)
in lithography is being explored to achieve smaller desired feature
sizes. Soft x-ray radiation may also be referred to as extreme
ultraviolet (EUV) radiation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 is a perspective view of an illumination system for
an Extreme Ultraviolet (EUV) lithography system.
[0005] FIG. 2 is a plan view of an array of hexagonal mirrors in a
multi-element pupil.
[0006] FIG. 3 is a flowchart describing a method for imaging a mask
pattern on a wafer using multiple sources of illumination.
[0007] FIG. 4 is a light combining section of an illumination
system.
[0008] FIG. 5 is a flowchart describing an alternative method for
imaging a mask pattern on a wafer using multiple sources of
illumination.
[0009] FIG. 6 is a perspective view of a scanning reticle receiving
light beams from multiple sources of illumination. The quality of
the diagrams has dropped and needs to be fixed.
[0010] FIG. 7 is a light combining section of an alternative
illumination system.
[0011] FIG. 8 is a flowchart describing a method for multiplexing
light from multiple sources.
[0012] FIG. 9 is a perspective view of a light combining section of
an illumination system utilizing rotating mirrors.
DETAILED DESCRIPTION
[0013] FIG. 1 illustrates an illumination system 100 for a
lithography system. In an embodiment, the lithography system may be
an Extreme Ultraviolet (EUV) lithography system. EUV lithography is
a projection lithography technique which may use a reduction
optical system and illumination in the soft X-ray spectrum
(wavelengths in the range of about 10 nm to 20 nm).
[0014] The system 100 may include multiple sources of EUV radiation
110-112, imaging collectors 115, a multi-element pupil 120, and
condenser optics 125. The optical elements in the system (e.g., the
imaging collectors 115, pupil 120, and condenser 125) may be
mirrors made to be reflective to EUV light of a particular
wavelength (typically 13.4 nm) by means of multilayer coatings
(typically of Mo and Si). Since EUV is strongly absorbed by
materials and gases, the lithography process may be carried out in
a vacuum, and a reflective, rather than transmissive, reticle mask
130 may be used.
[0015] In an embodiment, the sources 110-112 of soft X-rays may be
a compact high-average-power, high-repetition-rate laser which
impact a target material to produce broad band radiation with
significant EUV emission. The target material may be, for example,
a noble gas, such as Xenon (Xe), condensed into liquid or solid
form. The target material may convert a portion of the laser energy
into a continuum of radiation peaked in the EUV. Other approaches
may also be taken to produce the EUV plasma, such as driving an
electrical discharge through the noble gas.
[0016] The system 100 may combine the illumination from the
multiple sources 110-112 such that the light from the sources
overlap at the same image plane, e.g., the mask plane 130. This may
increase the available power of the system above that available
with a single source. For example, the sources in a multi-source
EUV lithography system may generate about 35 watts individually,
but may provide a power output of 70 watts or more when
combined.
[0017] The multi-element pupil 120 may include an array of
hexagonal mirrors. FIG. 2 shows a coordinate system for the
hexagonal mirrors in an array 200. Elliptical mirror sections may
be used as imaging collectors 115. Each source may have six
associated elliptical mirror sections. One foci of each elliptical
mirror section may be at one of the sources 110-112, and the second
foci of each elliptical mirror section may be at the center of one
of the hexagonal mirrors in the pupil array 120.
[0018] The designation "Source: x, y" in FIG. 2 identifies the
source (x) the hexagonal mirror is imaging and the number of the
elliptical mirror section (y) associated with source (x) that the
hexagonal mirror is imaging light from. For example, the hexagonal
mirror 205 with the designation "Source: 2, 3" images light from
elliptical mirror section number 3 focusing light from source 2.
The central hexagonal mirror 210 may receive no light. The distance
"r" on the axes refers to the distance from the center of hexagonal
mirror 210 to the position 215 at the center between the vertices
of three adjoining hexagonal mirrors. The center to vertices
distance for a hexagonal mirror may be about 0.9r. FIG. 3 is a
flowchart describing a method 300 for imaging a mask image onto a
wafer using multiple sources of radiation. The elliptical mirror
sections may create eighteen source images, e.g., six images of
each of the three sources 110-112 (block 305). Each of the eighteen
source images may be reflected onto one of the hexagonal mirrors in
the array 200, providing eighteen source images at the pupil 120
(block 310). The position and tilt of the hexagonal mirrors in
array 200 may be selected such that the central rays of the source
images hitting the hexagonal mirrors are reflected parallel to one
another (block 315).
[0019] The condenser optics 125 may produce a transformation of the
images at the pupil at the mask plane (block 320). The effect of
the transformation may be that light from all positions on the
hexagonal mirror array 200 with the same angle arrive at the same
position at the mask planes but at interleaved angles. In addition,
light leaving the array 200 from different angles may arrive at the
mask plane 130 at different positions. In this manner, the central
rays of the source images leaving in parallel from the array 200
may focus to a point at the center of the mask plane at interleaved
angles. The images may overlap and the illumination from the
multiple sources 110-112 may combine at the mask plane (block
325).
[0020] The radiation from the condenser 125 may be directed onto
the mask 130. The mask may include reflecting and absorbing
regions. The reflected EUV radiation from the mask 130 may carry an
IC pattern on the mask to a photoresist layer on a wafer. The
entire reticle may be exposed onto the wafer by synchronously
scanning the mask and the wafer, e.g., by a step-and-scan exposure
operation. Light from the mask is imaged on to the wafer using
projection optics.
[0021] The arrangement of the hexagonal mirrors in the array shown
in FIG. 2 may cause the reflected source images to interleave in
angle in a way that prevents variations in the power or intensity
from any one source from substantially changing the net weighted
position of the illumination at the pupil.
[0022] A consideration in designing optical systems is etendue.
Etendue is a conserved, invariant quantity in an optical system
that may be expressed as NA.sup.2.times.A=constant where NA is the
numerical aperture of the radiation incident at a surface of area
A. Etendue may represent a measure of the maximum beam size and
solid angle that can be accepted by an optical system.
[0023] The system may be designed such that the combined etendue of
the sources 110-112 may be less than or equal to the etendue
accepted by the production optics. If the etendue is consumed by
one of the sources, another source image may not be able to be
interleaved at the image plane.
[0024] In an alternative illumination system 400, a reflective mask
405, or reticle, may be illuminated by light from multiple sources
410-411 of EUV radiation, as shown in FIG. 4. The surface of the
reticle 405 may contain the pattern to be imaged on the wafer. In
an embodiment, an illuminator 415 may use an optical element, such
as a corner mirror 420, to combine the light from the EUV sources
410-411.
[0025] The lithography system in which the illumination system 400
is utilized may be a scanning system. In a scanning system, the
reticle and the wafer may be scanned simultaneously under the
illumination. The reticle and the wafer may be mounted on sliding
assemblies. The reticle may be illuminated with a rectangular beam
of light which scans across the patterned area as the reticle is
moved in a scanning direction. In an embodiment, a reduction ratio
demagnification in the scanning system may be 4.times.. In such a
system, the reticle may travel at a speed four times faster than
that of the wafer in order to have the image overlap properly.
[0026] FIG. 5 is a flowchart describing a method 500 for
illuminating a scanning reticle using multiple sources of
radiation. As shown in FIG. 6, light beams 610 and 611 from the
sources 410 and 411, respectively, may be directed onto the reticle
405 substantially adjacent to one another in the scanning direction
620 (block 505). The reticle 405 may be scanned under the
illumination (block 510) so that each part of the pattern receives
the same amount of integrated energy from the two beams. The
illumination may be begun before the beginning of the pattern and
stopped after the end of the pattern. The light beams may be
reflected from the reticle 405 onto the image plane such that the
pattern image is scanned on the wafer as the reticle is scanned
(block 515). A photoresist layer on the wafer may integrate the
energy from both sources (block 520).
[0027] The total etendue of the system may set the limit on the
number of sources which may be employed in the system.
[0028] As described above, EUV light may be strongly absorbed by
many materials, including optical elements in the system. In an
embodiment, the amount of light reflected from reflective surfaces
in an EUV lithography system may be about 67%. The inclusion of the
corner mirror 420 in the system may increase losses in EUV energy
in the optical path due to absorption by the added mirror 420.
[0029] In an alternative embodiment, the use of an additional
optical element, e.g., the corner mirror 420, in the optical path
may be avoided. Light beams 701-702 from multiple sources 705-706,
respectively, may be directed to a pupil 710 at different angles so
that they overlap at a position 720 on the transform plane at the
pupil, as shown in FIG. 7. As described above, a position at the
pupil 710 may correspond to an angle at the image plane at the mask
and an angle at the pupil may be transformed to a position at the
image plane 715. The angles may be selected such that the light
beams arrive at the image plane in positions 725 and 730, which are
parallel and adjacent to each other.
[0030] In another embodiment, light from multiple sources may be
multiplexed in time. FIG. 8 is a flowchart describing a method 800
for multiplexing light from multiple sources. As shown in FIG. 9,
two or more EUV light sources 900-904 may be focused at the same
focal point: 905, but at different angles (block 805). The light
from the multiple sources may be directed to the focal point 910
sequentially at a relatively high repetition rate e.g., several
kilohertz (block 810). A set of mirrors 910 on a rotating base 915
may be positioned under the point of focus 905 synchronously with
the repetition rate of the sources to align all of the reflections
to the same optical path 925 (block 815). The mirrors 910 may be
angled to direct the light from different sources arriving at
different angles along the optical path 920. A number of different
sets of mirrors may be rotated on the base to reduce the rate at
which the base must rotate. For example, in the system shown in
FIG. 9, five separate sets of five mirrors are rotated under the
five sources 900-904. Alternatively, a single moving mirror may be
used, but may need to be tilted and tipped at a precise angle and
at a precise time to correctly align the reflections from the
different sources.
[0031] A number of embodiments have been described. Nevertheless,
it will be understood that various modifications may be made
without departing from the spirit and scope of the invention. For
example, blocks in the flowcharts may be skipped or performed out
of order and still produce desirable results. Also, the
illumination system may be used in other lithography systems, e.g.,
an x-ray lithography system. Accordingly, other embodiments are
within the scope of the following claims.
* * * * *