U.S. patent application number 10/318319 was filed with the patent office on 2004-06-17 for planarization composition and method of patterning a substrate using the same.
This patent application is currently assigned to MOLECULAR IMPRINTS, INC.. Invention is credited to Smith, Britain J., Stacey, Nicholas A., Willson, C. Grant.
Application Number | 20040112862 10/318319 |
Document ID | / |
Family ID | 32506314 |
Filed Date | 2004-06-17 |
United States Patent
Application |
20040112862 |
Kind Code |
A1 |
Willson, C. Grant ; et
al. |
June 17, 2004 |
Planarization composition and method of patterning a substrate
using the same
Abstract
The present invention includes a composition and a method for
forming a pattern on a substrate with the composition by forming a
cross-linked polymer from the composition upon exposing the same to
radiation. To that end, in one embodiment of the present invention
the composition includes a non-silicon-containing acrylate
component, and an initiator component combined with said
non-silicon-containing acrylate to provide a viscosity no greater
than 5 cps. The initiator component is responsive to radiation to
initiate a free radical reaction and cause the non-silicon
containing acrylate component to polymerize and cross-link. One
embodiment of the non-silicon-containing acrylate component
includes ethylene glycol diacrylate. The method includes depositing
the composition to function as a planarization layer. Thereafter, a
layer of polymerizable material into which a pattern is to be
recorded is deposited.
Inventors: |
Willson, C. Grant; (Austin,
TX) ; Smith, Britain J.; (Austin, TX) ;
Stacey, Nicholas A.; (Austin, TX) |
Correspondence
Address: |
Kenneth C. Brooks
Legal Department
Molecular Imprints, Inc.
P.O. BOX 81536
Austin
TX
78708
US
|
Assignee: |
MOLECULAR IMPRINTS, INC.
Austin
TX
|
Family ID: |
32506314 |
Appl. No.: |
10/318319 |
Filed: |
December 12, 2002 |
Current U.S.
Class: |
216/66 |
Current CPC
Class: |
B82Y 10/00 20130101;
B29C 2043/025 20130101; B82Y 40/00 20130101; G03F 7/0955 20130101;
B81C 2201/0152 20130101; B29C 43/003 20130101; B81C 99/0085
20130101; G03F 7/0002 20130101 |
Class at
Publication: |
216/066 |
International
Class: |
C23F 001/00 |
Claims
What is claimed is:
1. A composition polymerizable in response to radiation being
incident thereupon, said composition comprising: a
non-silicon-containing acrylate component; and an initiator
component combined with said non-silicon-containing acrylate to
provide a viscosity no greater than 5 cps, with said initiator
component being responsive to said radiation to initiate a free
radical reaction to cause said non-silicon containing acrylate
component to polymerize and cross-link.
2. The composition as recited in claim 1 wherein said
non-silicon-containing acrylate component includes ethylene glycol
diacrylate.
3. A method of patterning a layer on a substrate, said method
comprising: forming a layer of polymerizable material on said
substrate; forming a planarization layer on said substrate,
positioned between said substrate and said layer of polymerizable
material, from a composition of a non-silicon-containing acrylate
component and an initiator component combined with said
non-silicon-containing acrylate to provide a viscosity no greater
than 5 cps, and swelling to no greater extent than to have greater
than 5% of said layer of polymerizable material penetrate said
planarization layer; contacting said layer of polymerizable
material with a surface of a mold to conform said layer of
polymerizable material to said surface; polymerizing said
planarization layer and said layer of polymerizable material by
impinging actinic radiation thereupon, to form polymerized
layers.
4. The method as recited in claim 3 wherein forming said
planarization layer further includes depositing a mixture of
ethylene glycol diacrylate and said initiator on said substrate and
contacting said mixture with a surface of a mold, with said surface
being substantially planar.
5. The method as recited in claim 3 further including providing
said mold with a pattern, with contacting said layer of
polymerizable material further including forming said pattern in
said layer of polymerizable material.
6. The method as recited in claim 5 further including separating
said mold from said polymerized layers and subjecting said
polymerized layers to an etching environment to transfer said
pattern into said substrate.
7. The method as recited in claim 3 wherein forming said layer of
polymerizable material further includes depositing, on said
substrate, a mixture having a mono-functional acrylate component, a
poly-functional molecule component; and a second initiator
component, an initiator component combined with said
mono-functional acrylate component and said poly-functional
molecule component to provide a viscosity no greater than 2 cps to
preferentially wet said surface forming a contact angle therewith
no greater than 75.degree., with said additional initiator
component being responsive to said radiation to initiate a free
radical reaction to cause said mono-functional acrylate component
and said poly-functional molecule component to polymerize and
cross-link.
8. The method as recited in claim 7 further including providing
said mixture with a silicon-containing acrylate component, wherein
said mono-functional acrylate component is less than 60% of said
composition, said silicon-containing acrylate component is less
than 50% of said solution, said poly-functional molecule component
is less than 20% of said solution and said initiator component is
less than 5% of said solution.
9. The method as recited in claim 7 wherein said mono-functional
acrylate component is selected from a set of acrylates consisting
of n-butyl acrylate, t-butyl acrylate and methyl methacrylate.
10. The method as recited in claim 7 wherein said poly-functional
molecule component includes a plurality of di-functional
molecules.
11. The method as recited in claim 7 wherein said poly-functional
molecule component is selected from a set of di-functional
molecules consisting of 1,3-bis (3-methacryloxypropyl)
tetramethyldisiloxane and ethylene diol diacrylate.
12. The method as recited in claim 7 wherein said initiator
component consists of molecules selected from a set consisting of
1-hydroxycyclohexyl phenyl ketone, 2-(2-hydroxypropyl) phenyl
ketone and phenylbis (2,4,6-trimethyl benzoyl) phosphine oxide.
Description
BACKGROUND OF THE INVENTION
[0001] The field of invention relates generally to
micro-fabrication of structures. More particularly, the present
invention is directed to patterning substrates in furtherance of
the formation of structures.
[0002] Micro-fabrication involves the fabrication of very small
structures, e.g., having features on the order of micro-meters or
smaller. One area in which micro-fabrication has had a sizeable
impact is in the processing of integrated circuits. As the
semiconductor processing industry continues to strive for larger
production yields while increasing the circuits per unit area
formed on a substrate, micro-fabrication becomes increasingly
important. Micro-fabrication provides greater process control while
allowing increased reduction of the minimum feature dimension of
the structures formed. Other areas of development in which
micro-fabrication has been employed include biotechnology, optical
technology, mechanical systems and the like.
[0003] An exemplary micro-fabrication technique is shown in U.S.
Pat. No. 6,334,960 to Willson et al. Willson et al. disclose a
method of forming a relief image in a structure. The method
includes providing a substrate having a transfer layer. The
transfer layer is covered with a polymerizable fluid composition. A
mold makes mechanical contact with the polymerizable fluid. The
mold includes a relief structure, and the polymerizable fluid
composition fills the relief structure. The polymerizable fluid
composition is then subjected to conditions to solidify and
polymerize the same, forming a solidified polymeric material on the
transfer layer that contains a relief structure complimentary to
that of the mold. The mold is then separated from the solid
polymeric material such that a replica of the relief structure in
the mold is formed in the solidified polymeric material. The
transfer layer and the solidified polymeric material are subjected
to an environment to selectively etch the transfer layer relative
to the solidified polymeric material such that a relief image is
formed in the transfer layer. The time required and the minimum
feature dimension provided by this technique is dependent upon,
inter alia, the composition of the polymerizable material.
[0004] It is desired, therefore, to provide improved compositions
of polymerizable materials for use in micro-fabrication.
SUMMARY OF THE INVENTION
[0005] The present invention includes a composition and a method
for forming a pattern on a substrate with the composition by
forming a cross-linked polymer from the composition upon exposing
the same to radiation. To that end, in one embodiment of the
present invention the composition includes a non-silicon-containing
acrylate component, and an initiator component combined with the
non-silicon-containing acrylate to provide a viscosity no greater
than 5 cps. The initiator component is responsive to radiation to
initiate a free radical reaction and cause the non-silicon
containing acrylate component to polymerize and cross-link. One
embodiment of the non-silicon-containing acrylate component
includes ethylene glycol diacrylate. The method includes depositing
the composition to function as a planarization layer. Thereafter, a
layer of polymerizable material into which a pattern is to be
recorded is deposited. These and other embodiments are described
herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a simplified elevation view of a lithographic
system in accordance with the present invention;
[0007] FIG. 2 is a simplified representation of material from which
an imprinting layer, shown in FIG. 1, is comprised before being
polymerized and cross-linked;
[0008] FIG. 3 is a simplified representation of cross-linked
polymer material into which the material shown in FIG. 2 is
transformed after being subjected to radiation;
[0009] FIG. 4 is a simplified elevation view of an imprint device,
shown in FIG. 1, in mechanical contact with an imprint layer
disposed on a substrate, in accordance with one embodiment of the
present invention;
[0010] FIG. 5 is a simplified elevation view of the imprint device
spaced-apart from the imprint layer, shown in FIG. 4, after
patterning of the imprint layer;
[0011] FIG. 6 is a simplified elevation view of the imprint device
and imprint layer shown in FIG. 5, with residue remaining in the
pattern; and
[0012] FIG. 7 is a simplified elevation view of material in an
imprint device and substrate employed with the present invention in
accordance with an alternate embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0013] Referring to FIG. 1, a lithographic system in accordance
with an embodiment of the present invention includes a substrate
10, having a substantially planar region shown as surface 12.
Disposed opposite substrate 10 is an imprint device 14 having a
plurality of features thereon, forming a plurality of spaced-apart
recesses 16 and protrusions 18. In the present embodiment, the
recesses 16 are a plurality of grooves extending along a direction
parallel to protrusions 18 that provide a cross-section of imprint
device 14 with a shape of a battlement. However, the recesses 16
may correspond to virtually any feature required to create an
integrated circuit. A translation mechanism 20 is connected between
imprint device 14 and substrate 10 to vary a distance "d" between
imprint device 14 and substrate 10. A radiation source 22 is
located so that imprint device 14 is positioned between radiation
source 22 and substrate 10. Radiation source 22 is configured to
impinge radiation on substrate 10. To realize this, imprint device
14 is fabricated from material that allows it to be substantially
transparent to the radiation produced by radiation source 22.
[0014] Referring to both FIGS. 1 and 2, an imprinting layer 24 is
disposed adjacent to surface 12, between substrate 10 and imprint
device 14. Although imprinting layer 24 may be deposited using any
known technique, in the present embodiment, imprinting layer 24 is
deposited as a plurality of spaced-apart discrete beads 25 of
material 25a on substrate 10, discussed more fully below.
Imprinting layer 24 is formed from a material 25a that may be
selectively polymerized and cross-linked to record a desired
pattern. Material 25a is shown in FIG. 3 as being cross-linked at
points 25b, forming cross-linked polymer material 25c.
[0015] Referring to both FIGS. 1 and 4, the pattern recorded by
imprinting layer 24 is produced, in part, by mechanical contact
with imprint device 14. To that end, translation mechanism 20
reduces the distance "d" to allow imprinting layer 24 to come into
mechanical contact with imprint device 14, spreading beads 25 so as
to form imprinting layer 24 with a contiguous formation of material
25a, shown in FIG. 2, over surface 12. In one embodiment, distance
"d" is reduced to allow sub-portions 24a of imprinting layer 24 to
ingress into and fill recesses 16.
[0016] Referring to FIGS. 1, 2 and 4, to facilitate filling of
recesses 16, material 25a is provided with the requisite viscosity
to completely fill recesses 16 in a timely manner, while covering
surface 12 with a contiguous formation of material 25a, on the
order of a few milliseconds to a few seconds. In the present
embodiment, sub-portions 24b of imprinting layer 24 in
superimposition with protrusions 18 remain after the desired,
usually minimum distance "d" has reached a minimum distance,
leaving sub-portions 24a with a thickness t.sub.1, and sub-portions
24b with a thickness, t.sub.2. Thicknesses "t.sub.1" and "t.sub.2"
may be any thickness desired, dependent upon the application.
Further, in another embodiment, sub-portions 24b may be abrogated
entirely whereby the only remaining material from imprinting layer
24 are sub-portions 24a, after distance, "d" has reached a minimum
value.
[0017] Referring to FIGS. 1, 2 and 3, after a desired distance "d"
has been reached, radiation source 22 produces actinic radiation
that polymerizes and cross-links material 25a, forming cross-linked
polymer material 25c. As a result, the composition of imprinting
layer 24 transforms from material 25a to material 25c, which is a
solid. Specifically, material 25c is solidified to provide surface
24c of imprinting layer 24 with a shape conforming to a shape of a
surface 14a of imprint device 14, shown more clearly in FIG. 5.
[0018] Referring to FIGS. 1, 2 and 3 an exemplary radiation source
22 may produce ultraviolet radiation. Other radiation sources may
be employed, such as thermal, electromagnetic and the like. The
selection of radiation employed to initiate the polymerization of
the material in imprinting layer 24 is known to one skilled in the
art and typically depends on the specific application which is
desired. After imprinting layer 24 is transformed to consist of
material 25c, translation mechanism 20 increases the distance "d"
so that imprint device 14 and imprinting layer 24 are
spaced-apart.
[0019] Referring to FIG. 5, additional processing may be employed
to complete the patterning of substrate 10. For example, substrate
10 and imprinting layer 24 may be selectively etched to increase
the aspect ratio of recesses 30 in imprinting layer 24. To
facilitate etching, the material from which imprinting layer 24 is
formed may be varied to define a relative etch rate with respect to
substrate 10, as desired. The relative etch rate of imprinting
layer 24 to substrate 10 may be in a range of about 1.5:1 to about
100:1. Alternatively, or in addition to, imprinting layer 24 may be
provided with an etch differential with respect to photo-resist
material (not shown) selectively disposed on surface 24c. The
photo-resist material (not shown) may be provided to further
pattern imprinting layer 24, using known techniques. Any etch
process may be employed, dependent upon the etch rate desired and
the underlying constituents that form substrate 10 and imprinting
layer 24. Exemplary etch processes may include plasma etching,
reactive ion etching and the like.
[0020] Referring to FIGS. 2, 3 and 6, residual material 26 may be
present on imprinting layer 24 after patterning has been completed.
Residual material 26 may consist of un-polymerized material 25a,
solid polymerized and cross-linked material 25c, substrate 10 or a
combination thereof. Further processing may be included to remove
residual material 26 using well known techniques, e.g., argon ion
milling, a plasma etch, reactive ion etching or a combination
thereof. Further, removal of residual material 26 may be
accomplished during any stage of the patterning. For example,
removal of residual material 26 may be carried out before etching
the polymerized and cross-linked imprinting layer 24.
[0021] Referring to FIGS. 1 and 5, the aspect ratio of recesses 30
formed from the aforementioned patterning technique may be as great
as 30:1. To that end, one embodiment of imprint device 14 has
recesses 16 defining an aspect ratio in a range of 1:1 to 10:1.
Specifically, protrusions 18 have a width W.sub.1 in a range of
about 10 nm to about 5000 .mu.m, and recesses 16 have a width
W.sub.2 in a range of 10 nm to about 5000 .mu.m. As a result,
imprint device 14 may be formed from various conventional
materials, such as, but not limited to, quartz, silicon, organic
polymers, siloxane polymers, borosilicate glass, fluorocarbon
polymers, metal, and combinations of the above.
[0022] Referring to FIGS. 1 and 2, the characteristics of material
25a are important to efficiently pattern substrate 10 in light of
the unique deposition process employed. As mentioned above,
material 25a is deposited on substrate 10 as a plurality of
discrete and spaced-apart beads 25. The combined volume of beads 25
is such that the material 25a is distributed appropriately over
area of surface 12 where imprinting layer 24 is to be formed. As a
result, imprinting layer 24 is spread and patterned concurrently,
with the pattern being subsequently set by exposure to radiation,
such as ultraviolet radiation. As a result of the deposition
process it is desired that material 25a have certain
characteristics to facilitate rapid and even spreading of material
25a in beads 25 over surface 12 so that the all thicknesses t.sub.1
are substantially uniform and all thickness t.sub.2 are
substantially uniform. The desirable characteristics include having
a viscosity approximately that of water, (H.sub.2O), 1 to 2
centepoise (cps), or less, as well as the ability to wet surface of
substrate 10 to avoid subsequent pit or hole formation after
polymerization. To that end, in one example, the wettability of
imprinting layer 24, as defined by the contact angle method, should
be such that the angle, .theta..sub.1, is defined as follows:
0.gtoreq..theta..sub.1<75.degree.
[0023] With these two characteristics being satisfied, imprinting
layer 24 may be made sufficiently thin while avoiding formation of
pits or holes in the thinner regions, such as sub-portions 24b,
shown in FIG. 4.
[0024] Referring to FIGS. 2, 3 and 5, another desirable
characteristic that it is desired for material 25a to possess is
thermal stability such that the variation in an angle .PHI.,
measured between a nadir 30a of a recess 30 and a sidewall 30b
thereof, does not vary more than 10% after being heated to
75.degree. C. for thirty (30) minutes. Additionally, material 25a
should transform to material 25c, i.e., polymerize and cross-link,
when subjected to a pulse of radiation containing less than 5 J
cm-2. In the present example, polymerization and cross-linking was
determined by analyzing the infrared absorption of the "C.dbd.C"
bond contained in material 25a. Additionally, it is desired that
substrate surface 12 be relatively inert toward material 25a, such
that less than 500 nm of surface 12 be dissolved as a result of
sixty seconds of contact with material 25a. It is further desired
that the wetting of imprint device 14 by imprinting layer 24 be
minimized. To that end, the wetting angle, .theta..sub.2, should be
greater than 75.degree.. Finally, should it be desired to vary an
etch rate differential between imprinting layer 24 and substrate
10, an exemplary embodiment of the present invention would
demonstrate an etch rate that is 20% less than the etch rate of an
optical photo-resist (not shown) exposed to an oxygen plasma.
[0025] The constituent components that form material 25a to provide
the aforementioned characteristics may differ. This results from
substrate 10 being formed from a number of different materials. As
a result, the chemical composition of surface 12 varies dependent
upon the material from which substrate 10 is formed. For example,
substrate 10 may be formed from silicon, plastics, gallium
arsenide, mercury telluride, and composites thereof. Additionally,
substrate 10 may include one or more layers in region, e.g.,
dielectric layer, metal layers, semiconductor layer and the
like.
[0026] Referring to FIGS. 2 and 3, in one embodiment of the present
invention the constituent components of material 25a consist of
acrylated monomers or methacrylated monomers that are not silyated,
a cross-linking agent, and an initiator. The non-silyated acryl or
methacryl monomers are selected to provide material 25a with a
minimal viscosity, e.g., viscosity approximating the viscosity of
water (1-2 cps) or less. The cross-linking agent is included, even
though the size of these molecules increases the viscosity of
material 25a, to cross-link the molecules of the non-silyated
monomers, providing material 25a with the properties to record a
pattern thereon having very small feature sizes, on the order of a
few nanometers and to provide the aforementioned thermal stability
for further processing. To that end, the initiator is provided to
produce a free radical reaction in response to radiation, causing
the non-silyated monomers and the cross-linking agent to polymerize
and cross-link, forming a cross-linked polymer material 25c. In the
present example, a photo-initiator responsive to ultraviolet
radiation is employed. In addition, if desired, a silyated monomer
may also be included in material 25a to control the etch rate of
the resulting cross-linked polymer material 25c, without
substantially affecting the viscosity of material 25a.
[0027] Examples of non-silyated monomers include, but are not
limited to, butyl acrylate, methyl acrylate, methyl methacrylate,
or mixtures thereof. The non-silyated monomer may make up
approximately 25 to 60% by weight of material 25a. It is believed
that the monomer provides adhesion to an underlying organic
transfer layer, discussed more fully below.
[0028] The cross-linking agent is a monomer that includes two or
more polymerizable groups. In one embodiment, polyfunctional
siloxane derivatives may be used as a cross-linking agent. An
example of a polyfunctional siloxane derivative is
1,3-bis(3-methacryloxypropyl)-tetra- methyl disiloxane. Another
suitable cross-linking agent consists of ethylene diol diacrylate.
The cross-linking agent may be present in material 25a in amounts
of up to 20% by weight, but is more typically present in an amount
of 5 to 15% by weight.
[0029] The initiator may be any component that initiates a free
radical reaction in response to radiation, produced by radiation
source 22, shown in FIG. 1, impinging thereupon and being absorbed
thereby. Suitable initiators may include, but are not limited to,
photo-initiators such as 1-hydroxycyclohexyl phenyl ketone or
phenylbis(2,4,6-trimethyl benzoyl) phosphine oxide. The initiator
may be present in material 25a in amounts of up to 5% by weight,
but is typically present in an amount of 1 to 4% by weight.
[0030] Were it desired to include silylated monomers in material
25a, suitable silylated monomers may include, but are not limited
to, silyl-acryloxy and silyl methacryloxy derivatives. Specific
examples are methacryloxypropyl tris(tri-methylsiloxy)silane and
(3-acryloxypropyl)tris(tri-methoxysiloxy)-silane. Silylated
monomers may be present in material 25a in amounts from 25 to 50%
by weight. The curable liquid may also include a dimethyl siloxane
derivative. Examples of dimethyl siloxane derivatives include, but
are not limited to, (acryloxypropyl) methylsiloxane
dimethylsiloxane copolymer.
[0031] Referring to both FIGS. 1 and 2, exemplary compositions for
material 25a are as follows:
Composition 1
n-butyl
acrylate+(3-acryloxypropyltristrimethylsiloxy)silane+1,3-bis(3-met-
hacryloxypropyl)tetramethyldisiloxane
Composition 2
t-n-butyl
acrylate+(3-acryloxypropyltristrimethylsiloxy)silane+Ethylene diol
diacrylate
Composition 3
t-butyl
acrylate+methacryloxypropylpentamethyldisiloxane+1,3-bis(3-methacr-
yloxypropyl)tetramethyldisiloxane
[0032] The above-identified compositions also include stabilizers
that are well known in the chemical art to increase the operational
life, as well as initiators.
[0033] Referring to FIGS. 2 and 7, employing the compositions
described above in material 25a to facilitate imprint lithography
was achieved by defining a surface 112 of substrate 110 with a
planarization layer 32 disposed adjacent to a wafer 33. The primary
function of planarization layer 32 is to ensure surface 112 is
planar. To that end, planarization layer 32 may be formed from a
number of differing materials, such as, for example, thermoset
polymers, thermoplastic polymers, polyepoxies, polyamides,
polyurethanes, polycarbonates, polyesters, and combinations
thereof. It is desired that planarization layer 32 be formed from
material that polymerizes, or cures, in response to the actinic
radiation employed to cure imprinting layer 24 and adheres well
thereto and other adjacent layers and experiences less than 15%
shrinkage during curing. Planarization layer 32 should not
substantially penetrate imprinting layer 24. Specifically, it is
desired that planarization layer 32 is not swelled by the
imprinting layer 24 to the extent where there is more than 5% of
imprinting material 25a penetrating the planarization layer 32.
Additionally, it is desired that the material have a viscosity of
less than 5 cps and more particularly less than 2 cps at 20.degree.
C. A class of material that demonstrates these characteristics is
non-silicon-containing acrylates. An exemplary material is ethylene
glycol diacrylate combined with an initiator and stabilizers for
long shelf life. The initiator, may be any of those discussed above
and is responsive to actinic radiation, such as UV light and causes
a free radical which facilitates polymerization and cross-linking
of the ethylene glycol acrylate. Typically, the initiator does not
constitute more than 5% of the mixture. An exemplary initiator may
consist of molecules selected from a set consisting of
1-hydroxycyclohexyl phenyl ketone, 2-(2-hydroxypropyl) phenyl
ketone, available from Ciba Corporation under the trade name
Darocur 1173 and phenylbis (2,4,6-trimethyl benzoyl) phosphine
oxide.
[0034] Employing ethylene glycol diacrylate, planarization layer 32
is fabricated in a manner similar to imprinting layer 24 using a
featureless mold having a planar surface. In this manner,
planarization layer 32 is fabricated to possess a continuous,
smooth, relatively defect-free surface that may exhibit excellent
adhesion to the imprinting layer 24.
[0035] Additionally, to ensure that imprinting layer 24 does not
adhere to imprint device 14, surface 14a may be treated with a
modifying agent. One such modifying agent is a release layer 34
formed from a fluorocarbon silylating agent. Release layer 34 and
other surface modifying agents, may be applied using any known
process. For example, processing techniques that may include
chemical vapor deposition method, physical vapor deposition, atomic
layer deposition or various other techniques, brazing and the like.
In this configuration, imprinting layer 24 is located between
planarization layer 32 and release layer 34 during imprint
lithography processes.
[0036] The embodiments of the present invention described above are
exemplary. Many changes and modifications may be made to the
disclosure recited above, while remaining within the scope of the
invention. The scope of the invention should, therefore, be
determined not with reference to the above description, but instead
should be determined with reference to the appended claims along
with their full scope of equivalents.
* * * * *