U.S. patent application number 12/415013 was filed with the patent office on 2009-09-24 for applications of semiconductor nano-sized particles for photolithography.
This patent application is currently assigned to PIXELLIGENT TECHNOLOGIES LLC. Invention is credited to Zhiyun Chen, Gregory Cooper, Erin F. Fleet.
Application Number | 20090239161 12/415013 |
Document ID | / |
Family ID | 34375180 |
Filed Date | 2009-09-24 |
United States Patent
Application |
20090239161 |
Kind Code |
A1 |
Chen; Zhiyun ; et
al. |
September 24, 2009 |
APPLICATIONS OF SEMICONDUCTOR NANO-SIZED PARTICLES FOR
PHOTOLITHOGRAPHY
Abstract
Semiconductor nano-sized particles possess unique optical
properties, which make them ideal candidates for various
applications in the UV photolithography. In this patent several
such applications, including using semiconductor nano-sized
particles or semiconductor nano-sized particle containing materials
as highly refractive medium in immersion lithography, as
anti-reflection coating in optics, as pellicle in lithography and
as sensitizer in UV photoresists are described.
Inventors: |
Chen; Zhiyun; (Silver
Spring, MD) ; Fleet; Erin F.; (Springfield, VA)
; Cooper; Gregory; (Arlington, VA) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
PIXELLIGENT TECHNOLOGIES
LLC
College Park
MD
|
Family ID: |
34375180 |
Appl. No.: |
12/415013 |
Filed: |
March 31, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10792377 |
Mar 4, 2004 |
7524616 |
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12415013 |
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60451240 |
Mar 4, 2003 |
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Current U.S.
Class: |
430/5 |
Current CPC
Class: |
B82Y 30/00 20130101;
G03F 7/091 20130101; G03F 7/2041 20130101; G03F 7/004 20130101;
G03F 7/2002 20130101; G03F 1/62 20130101 |
Class at
Publication: |
430/5 |
International
Class: |
G03F 1/00 20060101
G03F001/00 |
Claims
1-8. (canceled)
9. A method of creating an anti-reflection coating on optics
comprising; applying, on said at least one optic, at least a thin
layer containing semiconductor nano-sized particles.
10. A method of claim 9 wherein the said semiconductor nano-sized
particles are selected from the group consisting of C, Si, Ge,
CuCl, CuBr, CuI, AgCl, AgBr, AgI, Ag.sub.2S, CaO, MgO, ZnO,
Mg.sub.xZn.sub.1-xO, ZnS, HgS, ZnSe, CdS, CdSe, CdTe, HgTe, PbS,
BN, AlN, GaN, Al.sub.xGa.sub.1-xN, GaP GaAs, GaSb, InP, InAs,
In.sub.xGa.sub.1-xAs, SiC, Si.sub.1-xGe.sub.x, Si.sub.3N.sub.4,
ZrN, CaF.sub.2, YF.sub.3, Al.sub.2O.sub.3, SiO.sub.2, TiO.sub.2,
Cu.sub.2O, Zr.sub.2O.sub.3, ZrO.sub.2, SnO.sub.2, YSi.sub.2,
GaInP.sub.2, Cd.sub.3P.sub.2, Fe.sub.2S, Cu.sub.2S,
CuIn.sub.2S.sub.2, MoS.sub.2, In.sub.2S.sub.3, Bi.sub.2S.sub.3,
CuIn.sub.2Se.sub.2, In.sub.2Se.sub.3, HgI.sub.2, PbI.sub.2,
Lanthanoids oxides, etc, and their various alloys.
11. A method of creating pellicle comprising; having at least a
thin layer containing semiconductor nano-sized particles.
12. A method of claim 11 wherein the said semiconductor nano-sized
particles are selected from the group consisting of C, Si, Ge,
CuCl, CuBr, CuI, AgCl, AgBr, AgI, Ag.sub.2S, CaO, MgO, ZnO,
Mg.sub.xZn.sub.1-xO, ZnS, HgS, ZnSe, CdS, CdSe, CdTe, HgTe, PbS,
BN, AlN, GaN, Al.sub.xGa.sub.1-xN, GaP GaAs, GaSb, InP, InAs,
In.sub.xGa.sub.1-xAs, SiC, Si.sub.1-xGe.sub.x, Si.sub.3N.sub.4,
ZrN, CaF.sub.2, YF.sub.3, Al.sub.2O.sub.3, SiO.sub.2, TiO.sub.2,
Cu.sub.2O, Zr.sub.2O.sub.3, ZrO.sub.2, SnO.sub.2, YSi.sub.2,
GaInP.sub.2, Cd.sub.3P.sub.2, Fe.sub.2S, Cu.sub.2S,
CuIn.sub.2S.sub.2, MoS.sub.2, In.sub.2S.sub.3, Bi.sub.2S.sub.3,
CuIn.sub.2Se.sub.2, In.sub.2Se.sub.3, HgI.sub.2, PbI.sub.2,
Lanthanoids oxides, etc, and their various alloys.
13. A method of using semiconductor nano-sized particles as
sensitizer in a photoresist.
14. A method of claim 13 wherein the said semiconductor nano-sized
particles are selected from the group consisting of C, Si, Ge,
CuCl, CuBr, CuI, AgCl, AgBr, AgI, Ag.sub.2S, CaO, MgO, ZnO,
Mg.sub.xZn.sub.1-xO, ZnS, HgS, ZnSe, CdS, CdSe, CdTe, HgTe, PbS,
BN, AlN, GaN, Al.sub.xGa.sub.1-xN, GaP GaAs, GaSb, InP, InAs,
In.sub.x,Ga.sub.1-xAs, SiC, Si.sub.1-xGe.sub.x, Si.sub.3N.sub.4,
ZrN, CaF.sub.2, YF.sub.3, Al.sub.2O.sub.3, SiO.sub.2, TiO.sub.2,
Cu.sub.2O, Zr.sub.2O.sub.3, ZrO.sub.2, SnO.sub.2, YSi.sub.2,
GaInP.sub.2, Cd.sub.3P.sub.2, Fe.sub.2S, Cu.sub.2S,
CuIn.sub.2S.sub.2, MoS.sub.2, In.sub.2S.sub.3, Bi.sub.2S.sub.3,
CuIn.sub.2Se.sub.2, In.sub.2Se.sub.3, HgI.sub.2, PbI.sub.2,
Lanthanoids oxides, etc, and their various alloys.
15. A method of performing photolithography comprising: projecting
light along an optical path to form a light pattern on a substrate
comprising a wafer that is at least in part coated with a layer
comprising photoresist, at least a portion of said light passing
through (a) at least one photomask with at least one pattern, (b) a
medium having semiconductor nano-sized particles dispersed therein,
and (c) at least an immediate next lens; said semiconductor
nano-sized particle dispersed medium is inserted between said
photomask and said immediate next lens; collecting, on said
photoresist, a portion of said light passing through said at least
one photomask, said semiconductor nano-sized particle dispersed
medium and said immediate next lens; and changing the solubility of
said photoresist at least in part in response to said collected
light pattern.
16. The method of claim 15 wherein said medium comprises a liquid,
polymer, or a gel.
17. The method of claim 16 wherein said medium comprises water.
18. The method of claim 15 wherein said nano-sized particle
dispersed medium is flowed continuously through the space between
said photomask and said immediate next lens.
19. The method of claim 18 wherein said medium comprises water.
20. The method of claim 15 wherein said nano-sized particle
dispersed medium is coated on said photomask.
21. The method of claim 15 wherein said nano-sized particle
dispersed medium is coated on said immediate next lens.
22. The method of claim 15 wherein the said semiconductor
nano-sized particles are selected from the group consisting of C,
Si, Ge, CuCl, CuBr, CuI, AgCl, AgBr, AgI, Ag.sub.2S, CaO, MgO, ZnO,
Mg.sub.xZn.sub.1-xO, ZnS, HgS, ZnSe, CdS, CdSe, CdTe, HgTe, PbS,
BN, AlN, GaN, Al.sub.xGa.sub.1-xN, GaP GaAs, GaSb, InP, InAs,
In.sub.x,Ga.sub.1-xAs, SiC, Si.sub.1-xGe.sub.x, Si.sub.3N.sub.4,
ZrN, CaF.sub.2, MgF.sub.2, YF.sub.3, Al.sub.2O.sub.3, SiO.sub.2,
TiO.sub.2, Cu.sub.2O, Zr.sub.2O.sub.3, ZrO.sub.2, SnO.sub.2,
YSi.sub.2, GaInP.sub.2,Cd.sub.3P.sub.2, Fe.sub.2S, Cu.sub.2S,
CuIn.sub.2S.sub.2, MoS.sub.2, In.sub.2S.sub.3, Bi.sub.2S.sub.3,
CuIn.sub.2Se.sub.2, In.sub.2Se.sub.3, HgI.sub.2, PbI.sub.2,
Lanthanoids oxides, and their various alloys.
23. The method of claim 15 wherein said semiconductor nano-sized
particles have bandgaps.
24. The method of claim 15 wherein said nano-sized particles are
transparent at least at one of lithographic wavelengths.
25. The method of claim 15 wherein said nano-sized particles
comprise nanocrystals.
26. The method of claim 15 wherein said light has a wavelength of
193 nm.
27. The method of claim 15 wherein said light has a wavelength of
157 nm.
28. The method of claim 15 wherein said light has a wavelength of
248 nm.
29. The method of claim 15 wherein said light has a wavelength of
365 nm.
30. The method of claim 15 wherein said nano-sized particle medium
fill up space between said photomask and said immediate next
lens.
31. The method of claim 15 wherein said photolithography is
immersion photolithography.
32. The method of claim 15 wherein said semiconductor nano-sized
particles have a refractive index higher than said medium.
33. The method of claim 32 wherein the said semiconductor
nano-sized particles are selected from the group consisting of C,
Si, Ge, CuCl, CuBr, CuI, AgCl, AgBr, AgI, Ag.sub.2S, CaO, MgO, ZnO,
Mg.sub.xZn.sub.1-xO, ZnS, HgS, ZnSe, CdS, CdSe, CdTe, HgTe, PbS,
BN, AlN, GaN, Al.sub.xGa.sub.1-xN, GaP GaAs, GaSb, InP, InAs,
In.sub.xGa.sub.1-xAs, SiC, Si.sub.1-xGe.sub.x, Si.sub.3N.sub.4,
ZrN, CaF.sub.2, MgF.sub.2, YF.sub.3, Al.sub.2O.sub.3, SiO.sub.2,
TiO.sub.2, Cu.sub.2O, Zr.sub.2O.sub.3, ZrO.sub.2, SnO.sub.2,
YSi.sub.2, GaInP.sub.2, Cd.sub.3P.sub.2, Fe.sub.2S, Cu.sub.2S,
CuIn.sub.2S.sub.2, MoS.sub.2, In.sub.2S.sub.3, Bi.sub.2S.sub.3,
CuIn.sub.2Se.sub.2, In.sub.2Se.sub.3, HgI.sub.2, PbI.sub.2,
Lanthanoids oxides, and their various alloys.
34. The method of claim 32 wherein said semiconductor nano-sized
particles have bandgaps.
35. The method of claim 32 wherein said nano-sized particles are
transparent at least at one of lithographic wavelengths.
36. The method of claim 32 wherein said nano-sized particles
comprise nanocrystals.
37. The method of claim 32 wherein said light has a wavelength of
193 nm.
38. The method of claim 32 wherein said light has a wavelength of
157 nm.
39. The method of claim 32 wherein said light has a wavelength of
248 nm.
40. The method of claim 32 wherein said light has a wavelength of
365 nm.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application claims the benefit of priority from
provisional application No. 60/451,240 filed Mar. 4, 2003,
incorporated herein by reference.
[0002] This application is related to US patent No. U.S. Pat. No.
6,291,110 B1, Cooper et al. entitled "Photolithographic System For
Exposing A Wafer Using A Programmable Mask"; and commonly-assigned
provisional application No. ______,filed ______ entitled
"Programmable photolithographic mask and reversible
photo-bleachable materials based on nano-sized semiconductor
particles and their applications" to Z. Chen et. al.
FIELD
[0003] This technology herein relates to photolithography, and more
particularly to applications of semiconductor nano-sized particles
in photolithography, and even more particularly to applications of
semiconductor nano-sized particles as highly refractive media in
immersion lithography, as anti-reflection coating, as pellicle, and
as sensitizer in UV photoresists.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0004] Not applicable.
BACKGROUND AND SUMMARY
Lithography
[0005] Generally, lithography is used to transfer a specific
pattern onto a surface. Lithography can be applied to transfer a
variety of patterns including, for example, painting, printing, and
the like. More recently, lithographic techniques have become
widespread for use in "microfabrication"--a major (but
non-limiting) example of which is the manufacture of integrated
circuits such as computer chips.
[0006] In a typical microfabrication operation, lithography is used
to define patterns for miniature electrical circuits. Lithography
defines a pattern specifying the location of metal, insulators,
doped regions, and other features of a circuit printed on a silicon
wafer or other substrate. The resulting circuit can perform any of
a number of different functions. For example, an entire computer
can be placed on a chip.
[0007] A primary lithography system includes a wafer stepper, a
photomask and photoresist. A wafer stepper generally consists of a
ultraviolet (UV) light source, a photomask holder, an optical
system for projecting and demagnifying the image of the mask onto a
photoresist-coated wafer, and a stage to move the wafer.
Conventional lithography also generally requires a photomask--a
quartz substrate with chrome patterns on one surface. The chrome
patterns form a perfect master of the pattern to be inscribed on
one layer of a chip. Also it requires photoresist to receive the
light pattern generated by the mask.
[0008] Improvements in lithography have been mainly responsible for
the explosive growth of computers in particular and the
semiconductor industry in general. The major improvements in
lithography are mainly a result of a decrease in the minimum
feature size (improvement in resolution). This improvement allows
for an increase in the number of transistors on a single chip (and
in the speed at which these transistors can operate). For example,
the computer circuitry that would have filled an entire room in
1960's technology can now be placed on a silicon "die" the size of
a thumbnail. A device the size of a wristwatch can contain more
computing power than the largest computers of several decades
ago.
[0009] The resolution of a photolithography system is described by
the Rayleigh equation:
d=k.sub.1.lamda./NA
where d is the minimum feature size, .lamda. is the wavelength, NA
is the numerical aperture of the optical system and k.sub.1 is a
constant determined by a specific system. For a certain wavelength
and a certain optical design, the only way to improve the
resolution is to increase the numerical aperture. The numerical
aperture is defined as:
NA=n sin .theta.
where n is the refraction index of the relative medium and .theta.
is the half angle of the cone of rays received by the entrance
pupil. High NA indicates high light collecting or light focusing
power. It is rather straightforward to see that the resolution is
proportional the refractive index of the medium.
Semiconductor Nano-sized Particles
[0010] Nano-sized particles are loosely defined as powders with
small diameters for example ranging from a few hundred nanometers
or less down to a few angstroms. Since they have generally only
been the focus of research in the last two decades, there is little
standardization, and they take many different names including
quantum dot, quantum sphere, quantum crystallite, nano-crystal,
micro-crystal, colloidal particle, nano-cluster, Q-particle or
artificial atom. Due to their small size, they often possess
dramatically different physical properties compared to their bulk
counterparts. Nano-sized particles have a wide range of
applications including metallurgy, chemical sensors,
pharmaceuticals, painting, and cosmetics. As a result of the rapid
development in synthesis methods in the last two decades, they have
now entered into microelectronic and optical applications.
Nano-sized particles with sizes less than 5 nm have been
synthesized from a variety of semiconductors, examples include C,
Si, Ge, CuCl, CuBr, CuI, AgCl, AgBr, AgI, Ag.sub.2S, CaO, MgO, ZnO,
ZnS, HgS, ZnSe, CdS, CdSe, CdTe, HgTe, PbS, BN, AlN, GaN, GaP GaAs,
GaSb, InP, InAs, In.sub.xGa.sub.1-xAs, SiC, Si.sub.1-xGe.sub.x,
Si.sub.3N.sub.4, ZrN, CaF.sub.2, YF.sub.3, Al.sub.2O.sub.3,
SiO.sub.2, TiO.sub.2, Cu.sub.2O, Zr.sub.2O.sub.3, SnO.sub.2,
YSi.sub.2, GaInP.sub.2, Cd.sub.3P.sub.2, Fe.sub.2S, Cu.sub.2S,
CuIn.sub.2S.sub.2, MoS.sub.2, In.sub.2S.sub.3, Bi.sub.2S.sub.3,
CuIn.sub.2Se.sub.2, In.sub.2Se.sub.3, HgI.sub.2, PbI.sub.2,
Lanthanoids oixides, etc. They have revealed very interesting
optical properties.
[0011] Semiconductor materials have the so called bandgaps. The
electron band below the bandgap is call valence band (VB) and the
electron band above the bandgap is called conduction band (CB). The
manifestation of a bandgap in optical absorption is that only
photons with energy larger than the bandgap are absorbed. A photon
with sufficient energy excites an electron from the top of valence
band to the bottom of conduction band, leaving an empty state, a
hole, at the top of the valence band.
[0012] There are several major advantages of using semiconductor
nano-sized particles in photolithography. First, the bandgap of
semiconductor nano-sized particles can be tailored by their size.
In a certain range the smaller the size, the larger the bandgap.
The bandgap determines the working wavelength.
[0013] Second, the refractive index can be very high near the
bandgap. Actually some semiconductors have the highest refractive
indices. For example wurzite TiO.sub.2 has a refractive index of
2.4, and wurzite GaN has a refractive index about 2.6 near the
bandgap. The refractive indices of common optical materials such as
fused silica and quartz used in the UV lithography are around 1.5.
This high refractive index is desirable for highly refractive
medium immersion lithography and optical coating.
[0014] Third, nano-sized particles can be easily coated onto optics
or wafers in the form of a thin film. They are, therefore, very
simple to handle and produce much less contamination. Because of
the polycrystalline nature of nano-sized particle films, there is
less concern about matching the thermal expansion coefficients
between the coating and the optics. Applying nano-sized particles
by coating provides least disturbance to the existing lithography
system.
[0015] Fourth, semiconductors nano-sized particles can reach sizes
much smaller than the working wavelength. Currently, a large number
of semiconductors can be fabricated into nano-sized particles
smaller than 5 nm in diameter. Hence the scattering from the
nanoparticles is negligible and size fluctuation of nano-sized
particles does not affect the final scattered and transmitted
light.
[0016] Fifth, in a broad sense semiconductors can possess bandgaps
as high as 12 eV, corresponding to a wavelength of 100 nm. For 157
nm lithography and beyond, few materials can withstand the
radiation except certain semiconductors. Nano-sized particles offer
a solution for the optics in these wavelengths.
[0017] Lastly, many semiconductor nano-sized particles can be
produced rather inexpensively. Therefore, the overall cost will
likely be lower than conventional methods.
[0018] We propose several applications of semiconductor nano-sized
particles in lithography. Such as highly refractive medium in
immersion lithography, optical coating, pellicle material, and
sensitizer in photoresists.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] These and other features and advantages will be better and
more completely understood by referring to the following detailed
description of presently preferred illustrative embodiments in
conjunction with the drawings, of which:
[0020] FIG. 1 shows an exemplary illustrative non-limiting optical
structure to achieve high resolution by inserting a layer of high
refractive index semiconductor nano-sized particle layer between
the photomask and the next optics in a projection photolithography
system;
[0021] FIG. 2 shows an exemplary illustrative non-limiting optical
structure to achieve high resolution by inserting a thin layer of
high refractive index containing semiconductor nano-sized particle
between the final optics and the photoresist in a projection
photolithography system;
[0022] FIG. 3 shows an exemplary illustrative non-limiting
antireflection coating for optical lens with a thickness of the
coating of .lamda./4 n for maximum transmission;
[0023] FIG. 4a is an exemplary illustrative non-limiting
photoresist with semiconductor nano-sized particles as
sensitizer;
[0024] FIG. 4b shows the exemplary physical process in which
photo-generated electron or hole are transferred out of the
particle via surface bonded acceptor or donor; and
[0025] FIG. 4c demonstrates the exemplary illustrative physical
process, i.e. Auger photo-ionization, in which electrons or holes
are ejected out the particle as a result of the incoming
photon.
DETAILED DESCRIPTION OF PRESENTLY PREFERRED EXAMPLE ILLUSTRATIVE
NON-LIMITING IMPLEMENTATIONS
[0026] It is shown in the Rayleigh equation that the resolution of
a lithography system is proportionally dependant on the refractive
index of the relevant medium. There are several examples of
achieving high resolution by immersion in high refractive index
liquid materials. However, the fact that all liquids used in the
liquid immersion lithography have refractive index smaller than 1.5
limits the final achievable resolution. Solid immersion lithography
has been proposed to achieve higher refractive index.
[0027] Nano-sized particles, as mentioned before, could offer much
higher refractive indices. Therefore, nano-sized particles, or
mixtures of nano-sized particles with certain liquid, polymer, gel
or solid material can improve the resolution in both liquid and
solid immersion lithography.
[0028] A first exemplary illustrative non-limiting application of
nano-sized particle as highly refractive medium in lithography is
demonstrated in FIG. 1. In projection lithography, a layer
containing nano-sized particles is inserted between the photomask
and the immediate next lens. This layer can be coated onto either
the photomask or the lens itself. For 365 nm lithography, this
layer may comprise ZnO or GaN nano-sized particles. For 193 nm
lithography, it may comprise Mg.sub.xZn.sub.1-xO or AlN or BN
nano-sized particles. The highly refractive layer has more
efficiency in collecting the light transmitted through the
photomask. Numerical aperture, as defined by NA=n sin .theta.,
describes the light-gathering power of a lens. In FIG. 1, by
inserting a high refractive layer between the mask and the first
lens, the numerical aperture is increased by a factor of n,
comparing to air. In air, NA cannot be larger than 1, while with
this coating NA can easily exceed 1. For example if TiO.sub.2
nano-sized particles are used, even with a NA=0.5 in air, the final
NA is 1.3.
[0029] This high light collecting efficiency offers great
advantages to the lithography system. First, if the geometry of the
entire optical system is kept the same, this added layer will
increase the final resolution by a factor of n. If the numerical
aperture, i.e. the resolution, is kept the same, then the diameter
of the optical system can be reduced by a factor of n and therefore
the overall cost of the system can be reduced. In particularly, in
programmable lithography, reduced size of optics means increase in
the throughput by roughly n.sup.2 (see "Photolithographic System
For Exposing A Wafer Using A Programmable Mask" by G. Cooper et.
al., US patent number U.S. Pat. No. 6,291,110 B1).
[0030] Another exemplary illustrative implementation is shown in
FIG. 2. In this non-limiting example the high refractive index
nano-sized particle containing layer is applied at the wafer end of
the lithography system. A layer containing nano-sized particle is
inserted between the photoresist and the exit of the projection
optical system. This layer may be simply deposited or spun on top
of the photoresist. This layer may also be formed by immersing the
space between the final optics and photoresist with nano-sized
particle containing highly refractive liquid, polymer or gel. This
layer may also be formed by continuously flowing highly refractive
liquid or gel through the space between the final optics and the
photoresist. The highly refractive liquid may contain nano-sized
particles and water. Again, as indicated by the Rayleigh equation,
the resolution of the system is increased by a factor of n. For
semiconductor nano-sized particles with refractive index bigger
than 2.5, this can be a significant improvement.
[0031] Another exemplary illustrative non-limiting arrangement is
to coat the numerical aperture limiting optics. In an imaging
system the numerical aperture is usually limited by the entrance
optics. In some systems, the numerical aperture may be limited by
some intermediated optics. To improve the overall NA, the specific
optics may be coated with highly refractive semiconductor
nano-sized particles containing material.
[0032] Another exemplary illustration is to fill the entire optical
system with semiconductor nano-sized particles or mixture of
nano-sized particle with liquid, polymer, gel or solid. Light
spreads more in the low refractive index material than in the high
refractive index material, filling up the entire space with high
refractive index material confines the light path to a tighter
distribution. Therefore, it can reduce the diameter of the optical
design further. This is particularly important to the programmable
lithography because smaller optics increase the throughput, see
"Photolithographic System For Exposing A Wafer Using A Programmable
Mask" by G. Cooper et. al., US patent number U.S. Pat. No.
6,291,110 B1.
[0033] For certain wavelengths in lithography such as 193 nm and
157 nm, few materials can withstand the highly energetic radiation
except some wide bandgap semiconductors such as MgO and AlN. The
high refractive index in these semiconductors also offers certain
advantages. For example, it will require less thickness to achieve
certain optical path, which is defined as refractive index times
the thickness. Smaller thickness in turn results in less
absorption.
[0034] An exemplary illustration of applying semiconductor
nano-sized particles for optical coating is the anti-reflection
coating of optical lenses, as demonstrated in FIG. 3.
Anti-reflection coating has an optical path of a quarter of the
wavelength, so the reflection is minimized. Of course, the coating
material itself has to cause little or no absorption at the working
wavelength. For optics working at 193 nm, Nano-sized particles such
as Mg.sub.xZn.sub.1-xO, BN, AlN, CaF.sub.2, MgF.sub.2, and
SiO.sub.2 may be used as the coating material because they all have
bandgap larger than the photon energy. For 157 nm lithography, AlN,
SiO.sub.2 nano-sized particles may be used. Nano-sized particles
can be mixed with certain decomposable polymer matrix, spun on to
the optics and then the matrix can removed through chemical
processes. Nano-sized particles may also be grown directly on the
optics by various know growth methods.
[0035] Another exemplary illustration is to use the semiconductor
nano-sized particles as pellicle materials. A pellicle provides
protection for a photomask against dust particles. The pellicle
itself may be transparent to the light and have certain mechanical
strength. For 193 nm pellicle, nano-sized particles such as
Mg.sub.xZn.sub.1-xO, BN, AlN, CaF.sub.2, MgF.sub.2, SiO.sub.2, may
be used as candidate materials. For 157 nm lithography, AlN,
SiO.sub.2 nano-sized particles may be used as candidate materials.
Few hundred micrometers of close-packed nano-sized particles may be
grown on a substrate, such as thin glass plate using suitable
methods. High pressure may be applied after the deposition to
assure mechanical strength. Then the substrate can be etched away
by selective etching, such as HF acid etching, leaving the free
standing film as the pellicle.
[0036] An exemplary illustration of applying semiconductor
nano-sized particles as a sensitizer in photoresist is shown in
FIG. 4. Nano-sized particles with certain bandgap(s) are mixed with
certain polymers as seen in the FIG. 4a. Upon absorption of a
photon, the resulted electron or hole may be transferred out of the
nano-sized particle into surrounding polymers via surface states or
surface bonded acceptor or donor. The transferred electrons or
holes can then break or form bonds in the polymer and alter its
solubility of the polymer to developers. This type of photoresist
can be used at wavelength shorter than 193 nm where it is difficult
to find conventional photoresists.
[0037] If nano-sized particles are small enough, multi-body
interactions such as Auger photo-ionization can be significant. As
depicted in FIG. 4b, in an Auger process, a photon generates a pair
of electron and hole, when the pair recombines, it transfer its
energy and momentum to another electron or hole. When multiple
Auger effects occur simultaneously, some of electrons or holes can
gain enough energy to be ejected out of the particle into the
surrounding environment. This process is described in the
publication entitled "Fluorescence Intermittency In Single Cadmium
Selenide Nanocrystals" to M. Nirmal et. al., Nature, 1996, 383, pp.
802-804. The ejected energetic electrons lose their energy by
breaking chemical bonds of the polymers. The broken bonds in turn
alter the solubility of the polymer to developer.
[0038] While the technology herein has been described in connection
with exemplary illustrative non-limiting embodiments, the invention
is not to be limited by the disclosure. The invention is intended
to be defined by the claims and to cover all corresponding and
equivalent arrangements whether or not specifically disclosed
herein.
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