U.S. patent application number 10/901627 was filed with the patent office on 2006-02-02 for passivation of multi-layer mirror for extreme ultraviolet lithography.
Invention is credited to Siegfried Schwarzl, Stefan Wurm.
Application Number | 20060024589 10/901627 |
Document ID | / |
Family ID | 35732657 |
Filed Date | 2006-02-02 |
United States Patent
Application |
20060024589 |
Kind Code |
A1 |
Schwarzl; Siegfried ; et
al. |
February 2, 2006 |
Passivation of multi-layer mirror for extreme ultraviolet
lithography
Abstract
A reflector structure suitable for extreme ultraviolet
lithography (EUVL) is provided. The structure comprises a substrate
having a multi-layer reflector. A capping layer is formed over the
multi-layer reflector to prevent oxidation. In an embodiment, the
capping layer is formed of an inert oxide, such as Al.sub.2O.sub.3,
HfO.sub.2, ZrO.sub.2, Ta.sub.2O.sub.5, Y.sub.2O.sub.3-stabilized
ZrO.sub.2, or the like. The capping layer may be formed by reactive
sputtering in an oxygen environment, by non-reactive sputtering
wherein the materials are sputtered directly from the respective
oxide targets, by non-reactive sputtering of the metallic layer
followed by full or partial oxidation (e.g., by natural oxidation,
by oxidation in oxygen-containing plasmas, by oxidation in ozone
(O.sub.3), or the like), by atomic level deposition (e.g., ALCVD),
or the like.
Inventors: |
Schwarzl; Siegfried;
(Neubiberg, DE) ; Wurm; Stefan; (Austin,
TX) |
Correspondence
Address: |
SLATER & MATSIL LLP
17950 PRESTON ROAD
SUITE 1000
DALLAS
TX
75252
US
|
Family ID: |
35732657 |
Appl. No.: |
10/901627 |
Filed: |
July 28, 2004 |
Current U.S.
Class: |
430/5 ;
430/966 |
Current CPC
Class: |
Y10T 428/12667 20150115;
G21K 1/062 20130101; G03F 7/70958 20130101; B82Y 10/00 20130101;
G03F 7/70316 20130101; G03F 7/70916 20130101 |
Class at
Publication: |
430/005 ;
430/966 |
International
Class: |
G03F 9/00 20060101
G03F009/00 |
Claims
1. A reflective device suitable for use in extreme ultraviolet or
soft x-ray applications, the reflective device comprising: a
substrate; a multi-layer reflector formed on the substrate; and a
capping layer formed on the multi-layer reflector, the capping
layer comprising an oxide that is chemically inert in an oxidizing
environment.
2. The reflective device of claim 1, wherein the substrate
comprises a low-thermal expansion material (LTEM).
3. The reflective device of claim 2, wherein the substrate
comprises ultra-low expansion (ULE) glass.
4. The reflective device of claim 2, wherein the substrate
comprises Zerodur.RTM..
5. The reflective device of claim 1, wherein the multi-layer
reflector comprises alternating layers of a high atomic number Z
material and a low atomic number Z material.
6. The reflective device of claim 5, wherein the high atomic number
Z material comprises molybdenum.
7. The reflective device of claim 5, wherein the low atomic number
Z material comprises silicon.
8. The reflective device of claim 5, wherein each pair of the high
atomic number Z material and the low atomic number Z material is
about 6.8 nm in thickness.
9. The reflective device of claim 1, wherein the capping layer
comprises Al.sub.2O.sub.3, HfO.sub.2, ZrO.sub.2, Ta.sub.2O.sub.5,
Y.sub.2O.sub.3-stabilized ZrO.sub.2, or a combination thereof.
10. The reflective device of claim 1, wherein the capping layer
comprises a plurality of layers.
11. The reflective device of claim 1, wherein the capping layer is
about 1 nm to about 5 nm in thickness.
12. A method of forming a reflective device suitable for use in
extreme ultraviolet or soft x-ray applications, the method
comprising: providing a substrate having a multi-layer reflector
formed thereon; and forming a capping layer over the multi-layer
reflector, the capping layer comprising an oxide that is chemically
inert in an oxidizing environment.
13. The method of claim 12, wherein the substrate comprises a
low-thermal expansion material (LTEM).
14. The method of claim 13, wherein the substrate comprises
ultra-low expansion (ULE) glass.
15. The method of claim 13, wherein the substrate comprises
Zerodur.RTM..
16. The method of claim 12, wherein the multi-layer reflector
comprises alternating layers of a high atomic number Z material and
a low atomic number Z material.
17. The method of claim 16, wherein the high atomic number Z
material comprises molybdenum.
18. The method of claim 16, wherein the low atomic number Z
material comprises silicon.
19. The method of claim 16, wherein each pair of the high atomic
number Z material and the low atomic number Z material is about 6.8
nm in thickness.
20. The method of claim 16, wherein the capping layer comprises
Al.sub.2O.sub.3, HfO.sub.2, ZrO.sub.2, Ta.sub.2O.sub.5,
Y.sub.2O.sub.3-stabilized ZrO.sub.2, or a combination thereof.
21. The method of claim 12, wherein the capping layer comprises a
plurality of layers.
22. The method of claim 12, wherein the capping layer is about 1 nm
to about 5 nm in thickness.
23. The method of claim 12, wherein the forming comprises
performing a reactive sputter process in an oxygen atmosphere using
metallic sputter targets.
24. The method of claim 12, wherein the forming comprises
performing a non-reactive sputter process wherein the inert oxide
is sputtered directly from a respective oxide target.
25. The method of claim 12, wherein the forming comprises
performing a non-reactive sputter process of a metallic layer and
fully or partially oxidizing the metallic layer.
26. The method of claim 12, wherein the forming comprises
performing an atomic layer deposition process.
27. A method of patterning a semiconductor device, the method
comprising: providing a semiconductor wafer; applying a photoresist
material; and exposing a portion of the photoresist material, the
exposing using a reflective device suitable for use in extreme
ultraviolet or soft x-ray applications, the reflective device
having a capping layer over a multi-layer reflector, the capping
layer comprising an oxide that is chemically inert in an oxidizing
environment.
28. The method of claim 27, wherein the reflective device further
comprises a substrate formed of a low-thermal expansion material
(LTEM).
29. The method of claim 28, wherein the substrate comprises
ultra-low expansion (ULE) glass.
30. The method of claim 28, wherein the substrate comprises
Zerodur.RTM..
31. The method of claim 27, wherein the multi-layer reflector
comprises alternating layers of a high atomic number Z material and
a low atomic number Z material.
32. The method of claim 31, wherein the high atomic number Z
material comprises molybdenum.
33. The method of claim 31, wherein the low atomic number material
comprises silicon.
34. The method of claim 31, wherein each pair of the high atomic
number Z material and the low atomic number Z material is about 6.8
nm in thickness.
35. The method of claim 27, wherein the capping layer comprises
Al.sub.2O.sub.3, HfO.sub.2, ZrO.sub.2, Ta.sub.2O.sub.5,
Y.sub.2O.sub.3-stabilized ZrO.sub.2, or a combination thereof.
36. The method of claim 27, wherein the capping layer comprises a
plurality of layers.
37. The method of claim 27, wherein the capping layer is about 1 nm
to about 5 nm in thickness.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to semiconductor
fabrication, and more particularly to EUV lithography.
BACKGROUND
[0002] Generally, photolithography techniques used in the
fabrication of semiconductor devices utilize an imaging system that
directs radiation onto a mask to form a pattern. The pattern is
projected onto a semiconductor wafer covered with light-sensitive
photoresist. Once exposed, the photoresist material may be
developed to remove excess photoresist material. The remaining
photoresist material acts as an etching mask for an etching process
used to pattern the underlying semiconductor wafer.
[0003] Ongoing improvements in lithography have allowed the size of
semiconductor integrated circuits (ICs) to be reduced, thereby
allowing devices with higher density and better performance. One
highly promising lithography system uses radiation in the extreme
ultraviolet (EUV) wavelength range. Generally, EUV lithography
(EUVL) uses radiation having wavelengths of about 10 to 15 nm
located between the soft x-ray and the vacuum ultra-violet (VUV)
wavelength range.
[0004] Generally, EUVL imaging systems are reflective systems. EUV
reflective systems, which may be used as an illuminator, projection
optics, reflective optics, condenser optics, reflective photo
masks, or the like, use multi-layer, thin-film coatings known as
distributed Bragg reflectors. The multi-layer coatings typically
comprise 40-70, or more, Mo/Si bi-layers with the bi-layer
thickness being about half of the respective EUV wavelength being
used.
[0005] During use, however, the surface of the EUV reflective
optics including reflective masks which are also considered to be
optical elements frequently become contaminated. Surface oxidation
and carbon deposits are particularly troublesome and can shorten
the useful life of the EUV reflective optics such that the use of
EUV reflective optics is not commercially feasible. Carbon deposits
occur due to the absorption of CH-containing molecules
(hydrocarbons) on the optics surface from residual gases in the
vacuum environment or absorption of carbon containing molecules
(CO, CO.sub.2) and subsequent photon- or secondary electron induced
dissociation and desorption reactions. Resist outgassing may also
lead to carbon deposition on the mirror surfaces through
photodissociation or through electron-induced dissociation by
photon generated secondary electrons of hydrocarbons. Surface
oxidation may result from residual water vapor through absorption
of water and subsequent photon-induced or secondary
electron-induced dissociation of H.sub.2O where the oxygen remains
on the surface and the hydrogen desorbs.
[0006] Carbon contaminates may be removed reversibly by controlled
introduction of oxidizing gases such as H.sub.2O. However, the
partial pressures of hydrocarbon-containing gases and water vapor
pressure must be tightly controlled within a very small process
window that prevents oxidation without leaving too much carbon on
the surface. The process is further complicated because EUV optics
in an EUV exposure tool are exposed to different EUV intensities
and the process window may be different for each mirror.
Furthermore, during EUV exposures oxidation is enhanced by
generation of highly reactive radicals (e.g., O, OH) via
dissociation of gas phase molecules by the intense EUV radiation
above the mirror surfaces. The generation of radicals may be
different for different light intensities and, therefore, for
different mirrors.
[0007] Attempts have been made to solve this oxidation problem by
adding capping layers of silicon, ruthenium, and layers of silicon
and ruthenium modified by adding oxygen and/or nitrogen over the
surface of the EUV optics. However, it has been found that these
capping layers were not oxidation resistant and did not provide an
effective barrier layer against diffusion of oxides, e.g., O.sub.2,
O, OH, or the like, such that the capping layers were penetrated by
these molecules and/or atoms which then oxidized the multi-layer
stack below the capping layer causing changes of the optical
constants and the thicknesses of the individual layers.
[0008] Therefore, what is needed is an EUV optics structure that
resists contamination by carbon and oxidation.
SUMMARY OF THE INVENTION
[0009] These and other problems are generally solved or
circumvented, and technical advantages are generally achieved, by
preferred embodiments of the present invention which provides an
EUV reflective optics structure that may be used, for example, in
EUV lithography.
[0010] In accordance with an embodiment of the present invention, a
reflective device suitable for use in extreme ultraviolet or soft
x-ray applications is provided. The reflective device comprises a
substrate having a multi-layer reflector. A capping layer is formed
over the multi-layer reflector to prevent oxidation. In an
embodiment, the capping layer comprises an inert oxide, such as
Al.sub.2O.sub.3, HfO.sub.2, ZrO.sub.2, Ta.sub.2O.sub.5,
Y.sub.2O.sub.3-stabilized ZrO.sub.2, or the like.
[0011] In accordance with another embodiment of the present
invention, a method of forming a reflective device suitable for use
in extreme ultraviolet or soft x-ray applications is provided. The
method includes forming a capping layer over a multi-layer
reflector on a substrate. The capping layer may be formed by
reactive sputtering in an oxygen environment, by non-reactive
sputtering wherein the materials are sputtered directly from the
respective oxide targets, by non-reactive sputtering of the
metallic layer followed by full or partial oxidation (e.g., by
natural oxidation, by oxidation in oxygen-containing plasmas, by
oxidation in ozone (O.sub.3), or the like), by atomic level
deposition (e.g., ALCVD), or the like.
[0012] In accordance with yet another embodiment of the present
invention, a method of patterning a semiconductor device is
provided. The method utilizes an EUVL system having one or more
reflective devices, wherein at least one of the reflective devices
have a capping layer formed over a multi-layer reflector. The
capping layer prevents or reduces the oxidation of the multi-layer
reflector during operation.
[0013] It should be appreciated by those skilled in the art that
the conception and specific embodiment disclosed may be readily
utilized as a basis for modifying or designing other structures or
processes for carrying out the same purposes of the present
invention. It should also be realized by those skilled in the art
that such equivalent constructions do not depart from the spirit
and scope of the invention as set forth in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] For a more complete understanding of the present invention,
and the advantages thereof, reference is now made to the following
descriptions taken in conjunction with the accompanying drawings,
in which:
[0015] FIG. 1 illustrates an EUV optics structure in accordance
with an embodiment of the present invention; and
[0016] FIG. 2 illustrates an EUVL system in accordance with an
embodiment of the present invention.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0017] The making and using of the presently preferred embodiments
are discussed in detail below. It should be appreciated, however,
that the present invention provides many applicable inventive
concepts that can be embodied in a wide variety of specific
contexts. The specific embodiments discussed herein are merely
illustrative of specific ways to make and use the invention, and do
not limit the scope of the invention.
[0018] Referring now to FIG. 1, a cross section of an EUV
multi-layer reflector 100 is shown in accordance with an embodiment
of the present invention. The EUV multi-layer reflector 100
comprises a substrate 110, a multi-layer reflector 112, and a
capping layer 114. Preferably, the substrate 110 is formed of a
low-thermal expansion material (LTEM) such as ultra-low expansion
(ULE) glass available from Corning, Incorporated. Alternatively,
other materials, such as Zerodur.RTM. manufactured by Schott Glass
Technologies or the like, may be used.
[0019] The multi-layer reflector 112 comprises alternating layers
of a high atomic number Z material and a low atomic number Z
material with both materials selected for low absorption index and
preferably about 40-70 pairs of alternating layers. In an
embodiment, the high atomic number Z material comprises molybdenum,
and the low atomic number Z material comprises silicon. In this
embodiment, it is preferred that the pair of molybdenum and silicon
layers is between about 5 and about 7.5 nm (i.e., about half of the
EUV wavelength of about 10-15 nm) in thickness. Thus, the thickness
of the multi-layer reflector 112 may be about 200 nm to about 525
nm. In a preferred embodiment in which plasma sources having a
wavelength of about 13.5 nm are used, each pair of alternating
molybdenum and silicon layers has a thickness of about 6.8 nm. It
should be noted that the preferred thickness is dependent upon the
angle of incidence of the EUV radiation on the specific multi-layer
reflector. Other thicknesses, materials, and number of layers may
be used.
[0020] The capping layer 114 is preferably formed of one or more
thin layers of a material that provide good diffusion barrier
properties against oxidation of the underlying multi-layer
reflector and allow for effective removal of carbon contaminates.
In a preferred embodiment, the capping layer comprises aluminum
Al.sub.2O.sub.3, about 1 to about 5 nm in thickness, formed by
reactive sputtering in an oxygen environment. Suitable methods for
forming the cap layer include a DC or AC magnetron sputtering or
ion beam deposition. The former is a diode sputtering method in
which magnetic fields at the target (cathode) cause intense local
plasma densities and thus high sputter rates. In ion beam
sputtering deposition systems, ion beams from a separate ion source
are obliquely directed to the remote target. Reactive sputtering in
either method includes sputtering of a metallic target, in the case
of Al.sub.2O.sub.3 this is metallic aluminum. Process gases that
may be used include argon with an addition of about 10% to about
20% oxygen that reacts with the ejected aluminum atoms from the
target surface. It is desirable to have a precise partial pressure
control of oxygen to avoid poisoning (oxidation) of the target
resulting in large changes of sputter rates. Both types of
sputtering systems are preferably comprised of single or multi
target systems, UHV design, single substrate processing, and
dynamic or static deposition modes. In dynamic systems the
substrate is rotated and/or moved along a straight or a curved path
(e.g. using a planetary system) to achieve the necessary deposition
rate uniformity (<3% (3Sigma). Shaper plates may be used to
optimize uniformity. In this manner, the Al.sub.2O.sub.3 capping
layer has been found to be fabricated using relatively low process
temperatures (less than about 200.degree. C.) and yet provides
suitable diffusion barrier properties up to about 700.degree. C., a
temperature frequently considered beyond the maximum multi-layer
reflector temperatures occurring during fabrication of these
reflectors or during operation of the EUV exposure tool.
[0021] Other inert oxides, such as HfO.sub.2, ZrO.sub.2,
Ta.sub.2O.sub.5, Y.sub.2O.sub.3-stabilized ZrO.sub.2, and the like,
may also be used. Other processes, such as non-reactive sputtering
wherein the materials are sputtered directly from the respective
oxide targets, non-reactive sputtering of the metallic layer
followed by full or partial oxidation (e.g., by natural oxidation,
by oxidation in oxygen-containing plasmas, by oxidation in ozone
(O.sub.3), or the like), atomic level deposition (e.g., ALCVD), or
the like, may also be used.
[0022] It has been found that capping layers formed of these
materials provide a low surface roughness less than 0.2 nm and a
high thickness uniformity in the order of 10.sup.-2 to
5.times.10.sup.-2 nm. This creates a highly reflective surface
having low aberrations suitable for EUVL technologies and for 50 nm
and below designs. One of ordinary skill in the art will also
appreciate that the low process temperatures used to form the
capping layer prevents or reduces the amount of interdiffusion
between the layers of the reflector layer.
[0023] It has been found that a EUV reflector formed in this manner
allows carbon contaminates to be removed without the problem of
oxidation. For example, the carbon contaminates may be removed by
introduction of oxidizing gases such as H.sub.2O. In the prior art,
oxygen from the introduction of the oxidizing gases remain on the
EUV reflector surface (penetrating the capping layer, if any) and
oxidizes the Bragg reflectors, thereby decreasing performance
characteristics. In contrast, embodiments of the present invention
prevent or reduce the penetration of atomic and molecular oxygen,
thereby protecting the surface of the Bragg reflectors. The capping
layer also prevents or reduces the amount of oxidation that may
occur on the surface of the capping layer.
[0024] Referring now to FIG. 2, an EUVL system 200 is shown wherein
the optics utilize EUV optics formed in accordance with an
embodiment of the present invention. The EUVL system 200 comprises
a laser (or other radiation source) 210, condenser mirrors 212, a
reflective mask 214, reduction mirrors 216, and a semiconductor
wafer 218. Each of the mirrors may include a mirror having a
capping layer fabricated in accordance with an embodiment of the
present invention. Embodiments of the present invention may be used
with other imaging systems and configurations.
[0025] In operation, the condenser mirrors 212 collect and focus
the radiation generated by the laser 210 onto the reflective mask
214. The reflective mask 214, which is typically scanned, reflects
the desired pattern onto the reduction mirrors 216. The reduction
mirrors 216 reduce the size of the mask and project the mask having
the desired size onto the semiconductor wafer 218. As discussed
above, the use of the EUV optics in accordance with an embodiment
of the present invention provides a capping layer that provides an
oxidation barrier layer that prevents oxidation of the underlying
Bragg reflectors, thereby providing better reflectivity and a
longer useful life.
[0026] Although the present invention and its advantages have been
described in detail, it should be understood that various changes,
substitutions and alterations can be made herein without departing
from the spirit and scope of the invention as defined by the
appended claims. Moreover, the scope of the present application is
not intended to be limited to the particular embodiments of the
process, machine, manufacture, composition of matter, means,
methods and steps described in the specification. As one of
ordinary skill in the art will readily appreciate from the
disclosure of the present invention, processes, machines,
manufacture, compositions of matter, means, methods, or steps,
presently existing or later to be developed, that perform
substantially the same function or achieve substantially the same
result as the corresponding embodiments described herein may be
utilized according to the present invention. Accordingly, the
appended claims are intended to include within their scope such
processes, machines, manufacture, compositions of matter, means,
methods, or steps.
* * * * *