U.S. patent application number 13/615343 was filed with the patent office on 2014-03-13 for multi-layer work function metal replacement gate.
This patent application is currently assigned to INTERNATIONAL BUSINESS MACHINES CORPORATION. The applicant listed for this patent is Takashi Ando, Aritra Dasgupta, Unoh Kwon, Sean M. Polvino. Invention is credited to Takashi Ando, Aritra Dasgupta, Unoh Kwon, Sean M. Polvino.
Application Number | 20140070307 13/615343 |
Document ID | / |
Family ID | 50032735 |
Filed Date | 2014-03-13 |
United States Patent
Application |
20140070307 |
Kind Code |
A1 |
Ando; Takashi ; et
al. |
March 13, 2014 |
MULTI-LAYER WORK FUNCTION METAL REPLACEMENT GATE
Abstract
Embodiments relate to a field-effect transistor (FET)
replacement gate apparatus. The apparatus includes a channel
structure including a base and side walls defining a trench. A
high-dielectric constant (high-k) layer is formed on the base and
side walls of the trench. The high-k layer has an upper surface
conforming to a shape of the trench. A first layer is formed on the
high-k layer and conforms to the shape of the trench. The first
layer includes an aluminum-free metal nitride. A second layer is
formed on the first layer and conforms to the shape of the trench.
The second layer includes aluminum and at least one other metal. A
third layer is formed on the second layer and conforms to the shape
of the trench. The third layer includes aluminum-free metal
nitride.
Inventors: |
Ando; Takashi; (Tuckahoe,
NY) ; Dasgupta; Aritra; (Wappingers Falls, NY)
; Kwon; Unoh; (Fishkill, NY) ; Polvino; Sean
M.; (Brooklyn, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ando; Takashi
Dasgupta; Aritra
Kwon; Unoh
Polvino; Sean M. |
Tuckahoe
Wappingers Falls
Fishkill
Brooklyn |
NY
NY
NY
NY |
US
US
US
US |
|
|
Assignee: |
INTERNATIONAL BUSINESS MACHINES
CORPORATION
Armonk
NY
|
Family ID: |
50032735 |
Appl. No.: |
13/615343 |
Filed: |
September 13, 2012 |
Current U.S.
Class: |
257/330 ;
257/E29.262 |
Current CPC
Class: |
H01L 29/66545 20130101;
H01L 21/28088 20130101; H01L 29/517 20130101; H01L 29/66795
20130101; H01L 29/4966 20130101 |
Class at
Publication: |
257/330 ;
257/E29.262 |
International
Class: |
H01L 29/78 20060101
H01L029/78 |
Claims
1. A field-effect transistor (FET) replacement gate apparatus,
comprising: a channel structure including a base and side walls
defining a trench; a high-dielectric constant (high-k) layer formed
on the base and side walls of the trench and having an upper
surface conforming to a shape of the trench; a first layer formed
on the high-k layer and conforming to the shape of the trench, the
first layer comprising an aluminum-free metal nitride; a second
layer formed on the first layer and conforming to the shape of the
trench, the second layer comprising aluminum and at least one other
metal, a ratio of aluminum to the at least one other metal is a
gradient having a higher ratio at a center portion of the second
layer and a lower ratio at ends of the second layer; and a third
layer formed on the second layer and conforming to the shape of the
trench, the third layer comprising an aluminum-free metal
nitride.
2. The apparatus of claim 1, wherein the channel structure
comprises at least one of a substrate and an insulator formed on
the substrate.
3. The apparatus of claim 1, wherein the first and third layers
comprise one of titanium nitride (TiN) and tantalum nitride
(TaN).
4. The apparatus of claim 1, wherein the second layer includes
titanium and aluminum (TiAl).
5. The apparatus of claim 1, wherein the second layer does not
include nitrogen.
6. (canceled)
7. (canceled)
8. The apparatus of claim 1, wherein the aluminum and the at least
one other metal comprise atomic layers of the aluminum and the at
least one other metal, and the atomic layers of the aluminum exist
in greater concentrations in the center portion of the second layer
relative to the ends of the second layer.
9. The apparatus of claim 1, further comprising a metal gap fill
layer formed on the third layer to fill a gap defined by the trench
via the high-k layer, and the first, second, and third layers.
10. The apparatus of claim 1, wherein the FET is a finFET and the
side walls are at least one of source and drain structures and
channels extending between the source and drain structures.
11. The apparatus of claim 1, wherein the first layer includes no
oxygen.
12. A field-effect transistor replacement gate apparatus,
comprising: a substrate and side walls extending from the substrate
to form a trench; a high dielectric constant (high-k) layer formed
on at least the substrate; a first layer formed on the high-k
layer, the first layer comprising an aluminum-free metal nitride; a
second layer formed on the first layer, the second layer comprising
aluminum and at least one other metal, a ratio of the aluminum to
the at least one other metal being a gradient with a peak located
in a center region of the second layer and troughs located at ends
of the second layer; and a third layer formed on the second layer,
the third layer comprising an aluminum-free metal nitride.
13. The apparatus of claim 12, wherein the high-k layer includes
hafnium.
14. The apparatus of claim 12, wherein the first and third layers
comprise one of titanium nitride (TiN) and tantalum nitride
(TaN).
15. The apparatus of claim 12, wherein the second layer includes
titanium and aluminum (TiAl).
16. The apparatus of claim 12, wherein the second layer does not
include nitrogen.
17. The apparatus of claim 12, wherein layers of aluminum occur
with an increased frequency in the center region of the second
layer relative to the ends of the second layer.
18. The apparatus of claim 12, further comprising a metal gap fill
layer formed on the third layer to fill a gap defined by the trench
via the high-k layer, and the first, second, and third layers.
19. The apparatus of claim 12, wherein the FET is a finFET and the
side walls are at least one of source and drain structures and
channels extending between the source and drain structures.
20. The apparatus of claim 12, wherein the first layer includes no
oxygen.
Description
BACKGROUND
[0001] The present disclosure relates to a multi-layer work
function metal replacement gate, and in particular to layers of
work function metals that conform to a shape of a trench structure
and which are variable to adjust work function levels of a
replacement gate structure.
[0002] Field-effect transistors (FETs) generate an electric field,
by a gate structure, to control the conductivity of a channel
between source and drain structures in a semiconductor substrate.
The source and drain structures may be formed by doping the
semiconductor substrate, and the gate may be formed on the
semiconductor substrate between the source and drain regions.
Alternatively, a source and drain structure may be formed on the
substrate, and a channel may extend between the source and the
drain on the semiconductor substrate. In such a structure, referred
to as a finFET due to the fin-like shape of the channel, the gate
structure may be formed on the channel.
[0003] The gate of a finFET, and in some non-finFETs, may be formed
by a replacement gate process, or a process in which material, such
as dummy material, is removed to form a trench, and the gate
materials replace the removed material in the trench. In a finFET,
the trench may be defined by a plurality of channels and the source
and drain structures. In other FETs, as well as in finFETs, the
trench may be formed by insulating separators, for example. The
gate may be formed by depositing a work function metal in the
trench and forming a metal gap fill on the work function metal.
Titanium aluminum (TiAl) has been used as a replacement gate work
function metal, but TiAl has been limited to non-conformal methods
of application, such as physical vapor deposition (PVD), in which
an upper surface of the deposited material does not conform to a
shape of the surface on which the material is deposited, making
TiAl less-than-ideal as a replacement gate work function metal. In
addition, use of Al-based metal electrodes causes gate leakage
current degradation due to a strong oxygen gettering effect.
SUMMARY
[0004] Exemplary embodiments include a field-effect transistor
(FET) replacement gate apparatus. The apparatus includes a channel
structure including a base and side walls defining a trench. A
high-dielectric constant (high-k) layer is formed on the base and
side walls of the trench. The high-k layer has an upper surface
conforming to a shape of the trench. A first layer is formed on the
high-k layer. The first layer conforms to the shape of the trench.
The first layer includes an aluminum-free metal nitride. A second
layer is formed on the first layer and conforms to the shape of the
trench. The second layer includes aluminum and at least one other
metal. A third layer is formed on the second layer and conforms to
the shape of the trench. The third layer includes an aluminum-free
metal nitride.
[0005] Additional exemplary embodiments include a field-effect
transistor replacement gate apparatus. The apparatus includes a
substrate and side walls extending from the substrate to form a
trench. A high dielectric constant (high-k) layer is formed on at
least the substrate. A first layer is formed on the high-k layer.
The first layer includes an aluminum-free metal nitride. A second
layer is formed on the first layer. The second layer includes
aluminum and at least one other metal. The ratio of the aluminum to
the at least one other metal is a gradient with a peak located in a
center region of the second layer and troughs located at ends of
the second layer. The third layer is formed on the second layer.
The third layer includes an aluminum-free metal nitride.
[0006] Additional features and advantages are realized through the
techniques of the present disclosure. Other embodiments and aspects
of the present disclosure are described in detail herein and are
considered a part of the claimed disclosure. For a better
understanding of the disclosure with the advantages and the
features, refer to the description and to the drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0007] The subject matter of the disclosure is particularly pointed
out and distinctly claimed in the claims at the conclusion of the
specification. The forgoing and other features, and advantages of
the disclosure are apparent from the following detailed description
taken in conjunction with the accompanying drawings in which:
[0008] FIG. 1 illustrates a replacement gate structure according to
one embodiment of the present disclosure;
[0009] FIG. 2A illustrates a ratio of aluminum to another metal in
a layer of a group of work function metals according to one
embodiment;
[0010] FIG. 2B illustrates a ratio of aluminum to another metal in
a layer of a group of work function metals according to another
embodiment;
[0011] FIGS. 3A-3E illustrate a method of forming the replacement
gate structure according to one embodiment, in which:
[0012] FIG. 3A illustrates forming a high-dielectric-constant
material on a substrate;
[0013] FIG. 3B illustrates forming a first layer of a group of work
function metal layers;
[0014] FIG. 3C illustrates forming a second layer of a group of
work function metal layers;
[0015] FIG. 3D illustrates forming a third layer of a group of work
function metal layers;
[0016] FIG. 3E illustrates forming a gap fill metal layer; and
[0017] FIG. 4 illustrates a flowchart of a method for forming the
replacement gate structure according to one embodiment.
DETAILED DESCRIPTION
[0018] Conventional replacement gate work function metals suffer
from gate leakage current degradation due to material types and
processes for applying the materials. Disclosed embodiments relate
to work function metal layers that conform to a shape of a
replacement gate trench, reduce gate leakage current, and may have
an adjustable work function value.
[0019] FIG. 1 illustrates a replacement gate field-effect
transistor (FET) structure 100 according to one embodiment of the
present disclosure. The structure 100 includes a substrate 101,
which may be a semiconductor substrate, such as a silicon substrate
for example. The structure 100 includes side walls 102 extending
from the substrate 101. In one embodiment, the substrate is a doped
semiconductor substrate 101 having been doped to include source and
drain regions (not shown). In such an embodiment, the side walls
102 may be insulators. In another embodiment, the structure 100 is
a finFET structure, and the side walls 102 comprise channels or
fins 102 extending between a source and a drain structure formed on
the substrate 101. Alternatively, the side walls 102 may be the
source and drain structures formed on the substrate 101. The
substrate 101 and side walls 102 define a trench 103.
[0020] The structure 100 further includes a high-dielectric
constant (high-k) layer 104 formed on the side walls 102 and on the
substrate 101. The high-k layer 104 may be formed directly on the
substrate, for example. In one embodiment, the high-k layer 104
includes hafnium (Hf), such as hafnium dioxide (HfO.sub.2). In one
embodiment, the high-k layer 104 is formed to conform to the shape
of the trench 103. For example, the high-k layer 104 may be formed
by an atomic layer deposition (ALD) process which results in a
conforming layer.
[0021] The structure illustrated in FIG. 1 may correspond, for
example, to a finFET in which the side walls 102 are channels
extending between a source structure and a drain structure, or the
side walls 102 may be the source structure and the drain structure.
However, embodiments of the present disclosure also encompass
planar FET embodiments in which the side walls 102 are insulation
layers. In such a case, the high-k layer 104 may be formed either
to conform to the side walls 102 or may be formed only at the base
of the trench 104.
[0022] The structure 100 further includes a work function metal
layer group 105. The work function metal layer group 105 includes a
first layer 106 formed on the high-k layer 104, a second layer 107
formed on the first layer 106, and a third layer 108 formed on the
second layer 107. In one embodiment, the first layer 106 is formed
directly on the high-k layer 104, the second layer 107 is formed
directly on the first layer 106, and the third layer 108 is formed
directly on the second layer 107. In one embodiment, the first and
third layers comprise an aluminum-free metal nitride layer. For
example, the first and third layers 106 and 108 may be titanium
nitride (TiN) or tantalum nitride (TaN). In one embodiment, the
first layer 106 does not include oxygen. In one embodiment, the
second layer 107 is a metal layer including aluminum and at least
one other metal. For example, the second layer 107 may be made up
of titanium and aluminum (TiAl) without nitrogen, or the second
layer may be made up of titanium, aluminum and nitrogen
(TiAlN).
[0023] The second layer 107 may be formed to have varying ratios of
aluminum (Al) to another metal. Titanium (Ti) will be described in
the following example for purposes of clarity. However, embodiments
of the present disclosure encompass any appropriate metal in
combination with aluminum. The ratio of Al:(Al+Ti) may be adjusted
to adjust a work function of the structure 100. In one embodiment,
a ratio of Al:(Al+Ti) is substantially constant throughout the
entire second layer 107. The second layer 107 may be formed by ALD,
and the ratio may be maintained constant by depositing layers of Al
and Ti in a particular sequence. In one embodiment, the ratio of
Al:(Al+Ti) in the second layer is a gradient having a peak at a
center portion of the layer. The center portion may correspond, for
example, to about +/-10% of the height of the second layer 107 from
a center plane of the second layer 107. In such an embodiment,
layers of Al may be deposited in an ALD process with a greater
frequency when forming the center portion of the second layer 107
than when forming the end portions.
[0024] FIGS. 2A and 2B illustrate the ratio of Al to Al+Ti
according to embodiments of the present disclosure. As illustrated
in FIG. 2A, in one embodiment a ratio of Al to Al+Ti is zero in
regions corresponding to the first and third layers 106 and 108,
since these layers include no Al. In the region corresponding to
the second layer 107, the ratio of Al to Al+Ti is constant. In
other words, when forming the second layer 107 by ALD, a sequence
of deposition of Al and Ti layers may be maintained constant
throughout the formation of the second layer 107.
[0025] As illustrated in FIG. 2B, in another embodiment, a ratio of
Al to Al+Ti is still zero in regions corresponding to the first and
third layers 106 and 108, since these layers include no Al.
However, in the region corresponding to the second layer 107, the
ratio of Al to Al+Ti is a gradient that increases from the edges of
the second layer 107 and reaches a peak at a center region of the
second layer 107. In other words, when forming the second layer 107
by ALD, a sequence of deposition of Al and Ti layers may be
maintained altered so that layers of Al are deposited with
increased frequency relative to layers of Ti in the center region
of the second layer 107.
[0026] Referring again to FIG. 1, in addition to controlling the
work function of the structure 100 based on the ratio of Al:(Al+Ti)
in the second layer 107, embodiments of the present disclosure
further encompass controlling the work function of the structure
100 based on a thickness of the first layer 106. In one embodiment,
the thickness of the first layer 106 is formed or designed such
that the work function of the work function metal layers 105
corresponds to a quarter-gap work function. Embodiments of the
present disclosure further encompass controlling gate leakage
current levels by controlling the thickness of the first layer 106
and the ratio of Al:(Al+Ti) in the second layer 107.
[0027] In one embodiment, the first layer 106 has a thickness
between about 10 angstroms (.ANG.) and about 30 .ANG., the second
layer 107 has a thickness between about 10 A and about 60 A, and
the third layer 108 has a thickness between about 10 .ANG. and 30
.ANG..
[0028] The structure 100 further includes a gap fill metal 109
formed on the third layer 108. In one embodiment, the gap fill
metal 109 is formed directly on the third layer 108. The gap fill
metal 109 may be a non-conforming metal, or may be formed by a
non-conforming process, such as PVD. Alternatively, the gap fill
metal 109 may also be formed by a conforming process, such as ALD
or chemical vapor deposition (CVD). In one embodiment, the gap fill
metal 109 is aluminum. However, embodiments of the present
disclosure encompass any conductive metal.
[0029] FIGS. 3A to 3E illustrate a process for forming a
replacement gate structure 100 according to an embodiment of the
disclosure. FIGS. 3A to 3E illustrate a portion of the replacement
gate structure 100 around one replacement gate structure 100.
However, it is understood that the described layers may be of any
length and width dimensions, and multiple replacement gate
structures 100 may be formed. FIG. 4 is a flow diagram of a method
of forming a replacement gate structure according to an embodiment
of the present disclosure. The formation of the structure 100 will
be described below with reference to FIGS. 3A to 3E and 4.
[0030] In block 401 of FIG. 4, a substrate 100 is formed and side
walls 102 are formed. The substrate 101 may be a semiconductor
substrate or a silicon substrate. The substrate may be a doped
semiconductor substrate 101 having been doped to include source and
drain regions (not shown). In such an embodiment, the side walls
102 may be insulators. In another embodiment, the structure 100 is
a finFET structure, and the side walls 102 comprise channels or
fins 102 extending between a source and a drain structure formed on
the substrate 101. Alternatively, the side walls 102 may be the
source and drain structures formed on the substrate 101. The
substrate 101 and side walls 102 define a trench 103.
[0031] In block 402 and in FIG. 3A, a high-dielectric constant
(high-k) layer 104 is formed on the substrate 101 and side walls
102. The high-k layer 104 may be formed directly on the substrate
101, for example. In one embodiment, the high-k layer 104 includes
hafnium (Hf), such as hafnium dioxide (HfO.sub.2). In one
embodiment, the high-k layer 104 is formed to conform to the shape
of the trench 103. For example, the high-k layer 104 may be formed
by an atomic layer deposition (ALD) process which results in a
conforming layer. The ALD process is represented by arrows in FIGS.
3A to 3D.
[0032] In block 403 and in FIG. 3B, a first layer 106 is formed on
the high-k layer 104. The first layer 106 may be formed directly on
the high-k layer 104. The first layer 106 may be formed by a
conforming process. In one embodiment, the first layer 106 is
formed by ALD. The first layer may be an aluminum-free metal
nitride layer. For example, the first layer 106 may be titanium
nitride (TiN) or tantalum nitride (TaN). In one embodiment, the
first layer 106 does not include oxygen and is not modified during
fabrication of the structure 100 to include oxygen. In one
embodiment, a height of the first layer 106 is adjusted to adjust a
work function of the work function metal group 105 (see FIGS. 1 and
3E). In one embodiment, the thickness of the first layer 106 is
formed such that the work function of the work function metal group
105 corresponds to a quarter-gap work function. In one embodiment,
the first layer 106 has a thickness between about 10 .ANG. and
about 30 .ANG..
[0033] In block 404 and in FIG. 3C, a second layer 107 is formed on
the first layer 106. The second layer 107 may be formed directly on
the first layer 106. The second layer 107 may be formed by a
conforming process. In one embodiment, the second layer 107 is
formed by ALD. In one embodiment, the second layer 107 is a metal
layer including aluminum and at least one other metal. For example,
the second layer 107 may be made up of titanium and aluminum (TiAl)
without nitrogen. Alternatively, the second layer may be made up of
titanium, aluminum and nitrogen (TiAlN). The second layer 107 may
be formed by applying layers of Al and one or more additional
metals in sequential atomic layers in an ALD process. In an
embodiment in which the second layer 107 comprises TiAl, layers of
Ti and Al may be deposited in sequence in predetermined ratios.
[0034] In the embodiment in which the second layer includes TiAl,
the ratio of Al:(Al+Ti) may be adjusted to adjust a work function
of the structure 100. In one embodiment, a ratio of Al:(Al+Ti) is
substantially constant throughout the entire second layer 107. In
other words, layers of Al and Ti are deposited by an ALD process in
constant ratios. In one embodiment, the ratio of Al:(Al+Ti) in the
second layer is a gradient having a peak at a center portion of the
layer. The center portion may correspond, for example, to about
+/-10% of the height of the second layer 107 from a center plane of
the second layer 107. In such an embodiment, layers of Al may be
deposited in an ALD process with a greater frequency when forming
the center portion of the second layer 107 than when forming the
end portions, relative to a frequency with which the Ti layers are
deposited.
[0035] In one embodiment, the percentage of Al relative to Al+Ti in
the second layer 107 is between about 10% and about 90%. In one
embodiment, the second layer 107 is formed by depositing layers of
titanium nitride (TiN) and titanium aluminum nitride (TiAlN) in a
particular sequence to obtain a layer of TiAlN having a
predetermined ratio of Al:Ti, or a predetermined gradient of ratios
of Al:Ti throughout the second layer 107. The second layer 107 may
be formed to have a thickness between 10 .ANG. and 60 .ANG..
[0036] In block 405 and in FIG. 3D, a third layer 108 is formed on
the second layer 107. The third layer 108 may be formed directly on
the second layer 107. The third layer 108 may be formed by a
conforming process. In one embodiment, the third layer 108 is
formed by ALD. The third layer may be an aluminum-free metal
nitride layer. For example, the third layer 108 may be titanium
nitride (TiN) or tantalum nitride (TaN). In one embodiment, the
third layer 108 has a thickness between about 10 A and about 30 A.
The formation of the third layer 108 may prevent undesired
oxidation of the second layer 107 by air exposure.
[0037] In one embodiment, the first, second and third layers 106,
107 and 108 are formed in situ, or in a same chamber in sequential
order, without exposing the chamber to external air between the
deposition processes of the respective layers. In other words,
since the first, second and third layers 106, 107 and 108 may all
be formed by ALD, they may all be performed in the same chamber
without exposing the layers to air, and undesired oxidation of the
layers 106, 107 and 108 may be avoided.
[0038] In block 406 and in FIG. 3E a gap fill metal 109 is formed
on the third layer 108. The gap fill metal 109 may be formed
directly on the third layer 108. The gap fill metal 109 may be any
conductive metal, such as aluminum or tungsten. The gap fill metal
109 may be formed in a conforming process, such as ALD, or a
non-conforming process, such as PVD. In addition, a final
replacement gate structure 100 may be formed by removing, or
polishing off, the top surface layers down to the top surface of
the side walls 102 by chemical mechanical polish, for example. The
final replacement gate structure 100 is illustrated in FIG. 1.
[0039] Embodiments of the present disclosure encompass a
multi-layered work function metal group of a replacement gate
structure. The work function metal group includes a layer of
aluminum and at least one other metal between two layers of a metal
nitride that does not contain aluminum. The layers are formed on a
high-k layer, and all of the layers are formed by an ALD process to
conform to a shape of a substrate and side walls on which the
layers are formed. The layer including aluminum and at least one
other metal may have a higher concentration of aluminum towards a
center of the layer relative to the edges of the layer. The
concentration of aluminum may be adjusted according to
predetermined designs to achieve a particular work function, and to
reduce gate leakage current. In addition, the top-most
aluminum-free metal nitride layer prevents undesired oxidation of
the aluminum-containing layer by air exposure. In addition, the
entire metal group, and the high-k layer, may be formed by ALD to
be compatible with replacement gates, such as finFET
structures.
[0040] The flowchart and block diagrams in the Figures illustrate
the architecture, functionality, and operation of possible
implementations of embodiments of the present disclosure. It is
understood that in some alternative implementations, the functions
noted in the block may occur out of the order noted in the figures.
For example, two blocks shown in succession may, in fact, be
executed substantially concurrently, or the blocks may sometimes be
executed in the reverse order, depending upon the functionality
involved.
[0041] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the disclosure. As used herein, the singular forms "a", "an" and
"the" are intended to include the plural forms as well, unless the
context clearly indicates otherwise. It will be further understood
that the terms "comprises" and/or "comprising," when used in this
specification, specify the presence of stated features, integers,
steps, operations, elements, and/or components, but do not preclude
the presence or addition of one more other features, integers,
steps, operations, element components, and/or groups thereof.
[0042] The corresponding structures, materials, acts, and
equivalents of all means or step plus function elements in the
claims below are intended to include any structure, material, or
act for performing the function in combination with other claimed
elements as specifically claimed. The description of the present
disclosure has been presented for purposes of illustration and
description, but is not intended to be exhaustive or limited to the
disclosure in the form disclosed. Many modifications and variations
will be apparent to those of ordinary skill in the art without
departing from the scope and spirit of the disclosure. The
embodiment was chosen and described in order to best explain the
principles of the disclosure and the practical application, and to
enable others of ordinary skill in the art to understand the
disclosure for various embodiments with various modifications as
are suited to the particular use contemplated.
[0043] While exemplary embodiments of the disclosure have been
described, it will be understood that those skilled in the art,
both now and in the future, may make various improvements and
enhancements which fall within the scope of the claims which
follow. These claims should be construed to maintain the proper
protection for the disclosure first described.
* * * * *