U.S. patent application number 14/033326 was filed with the patent office on 2015-03-26 for dram mim capacitor using non-noble electrodes.
This patent application is currently assigned to Elpida Memory, Inc. The applicant listed for this patent is Elpida Memory, Inc, Intermolecular, Inc.. Invention is credited to Hanhong Chen, David Chi, Imran Hashim, Mitsuhiro Horikawa, Sandra G. Malhotra.
Application Number | 20150087130 14/033326 |
Document ID | / |
Family ID | 52575009 |
Filed Date | 2015-03-26 |
United States Patent
Application |
20150087130 |
Kind Code |
A1 |
Chen; Hanhong ; et
al. |
March 26, 2015 |
DRAM MIM Capacitor Using Non-Noble Electrodes
Abstract
A method for forming a capacitor stack includes forming a first
bottom electrode layer including a conductive metal nitride
material. A second bottom electrode layer is formed above the first
bottom electrode layer. The second bottom electrode layer includes
a conductive metal oxide material, wherein the crystal structure of
the conductive metal oxide material promotes a desired high-k
crystal phase of a subsequently deposited dielectric layer. A
dielectric layer is formed above the second bottom electrode layer.
Optionally, an oxygen-rich metal oxide layer is formed above the
dielectric layer. Optionally, a third top electrode layer is formed
above the oxygen-rich metal oxide layer. The third top electrode
layer includes a conductive metal oxide material. A fourth top
electrode layer is formed above the third top electrode layer. The
fourth top electrode layer includes a conductive metal nitride
material.
Inventors: |
Chen; Hanhong; (Milpitas,
CA) ; Chi; David; (Los Altos, CA) ; Hashim;
Imran; (Saratoga, CA) ; Horikawa; Mitsuhiro;
(Higashihiroshima, JP) ; Malhotra; Sandra G.;
(Fort Collins, CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Elpida Memory, Inc
Intermolecular, Inc. |
Tokyo
San Jose |
CA |
JP
US |
|
|
Assignee: |
Elpida Memory, Inc
Tokyo
CA
Intermolecular, Inc.
San Jose
|
Family ID: |
52575009 |
Appl. No.: |
14/033326 |
Filed: |
September 20, 2013 |
Current U.S.
Class: |
438/396 |
Current CPC
Class: |
H01L 28/40 20130101;
H01L 27/108 20130101; H01L 28/56 20130101; H01L 28/82 20130101;
H01L 28/75 20130101; H01L 27/1085 20130101 |
Class at
Publication: |
438/396 |
International
Class: |
H01L 49/02 20060101
H01L049/02 |
Claims
1. A method for forming a capacitor stack, the method comprising:
forming a first bottom electrode layer above a surface of a
substrate, wherein the first bottom electrode layer comprises a
conductive metal nitride material; forming a second bottom
electrode layer above the first bottom electrode layer, wherein the
second bottom electrode layer comprises a conductive metal oxide
material; forming a dielectric layer above the second bottom
electrode layer; forming an oxygen-rich metal oxide layer above the
dielectric layer; and forming a top electrode layer above the
oxygen-rich metal oxide layer, wherein the top electrode layer
comprises a conductive metal nitride material.
2. The method of claim 1, wherein the first bottom electrode layer
and the top electrode layer each comprises one of titanium nitride,
titanium aluminum nitride, titanium silicon nitride, tantalum
nitride, tantalum aluminum nitride, or tantalum silicon
nitride.
3. The method of claim 1, wherein the second bottom electrode layer
comprises one of molybdenum oxide, chromium oxide, cobalt oxide,
iridium oxide, manganese oxide, nickel oxide, ruthenium oxide, tin
oxide, or tungsten oxide.
4. The method of claim 1, wherein the second bottom electrode layer
comprises molybdenum oxide.
5. The method of claim 1, further comprising an anneal treatment
after forming the second bottom electrode layer above the first
bottom electrode layer and before forming the dielectric layer
above the second bottom electrode layer.
6. The method of claim 1, wherein the dielectric layer comprises
titanium oxide.
7. The method of claim 6, wherein the dielectric layer comprises
titanium oxide and the dielectric layer further comprises a
dopant.
8. The method of claim 7, wherein the dopant comprises
aluminum.
9. The method of claim 1, further comprising an anneal treatment
after forming the dielectric layer above the second bottom
electrode layer and before forming the oxygen-rich metal oxide
layer above the dielectric layer.
10. The method of claim 1, wherein the oxygen-rich metal oxide
layer comprises molybdenum oxide.
11. The method of claim 1, wherein forming the top electrode layer
comprises: forming a first top electrode layer above the
oxygen-rich metal oxide layer; and forming a second top electrode
layer above the first top electrode layer.
12. The method of claim 11, wherein the first top electrode layer
comprises a metal oxide material and the second top electrode layer
comprises a conductive metal nitride material.
13. The method of claim 12, wherein the second top electrode layer
comprises one of titanium nitride, titanium aluminum nitride,
titanium silicon nitride, tantalum nitride, tantalum aluminum
nitride, or tantalum silicon nitride.
14. The method of claim 11, wherein the first top electrode layer
comprises molybdenum oxide.
15. The method of claim 5, wherein the anneal treatment after
forming the second bottom electrode layer is performed in one of an
inert or a reducing atmosphere for between about 1 millsecond and
about 60 minutes.
16. The method of claim 9, wherein the anneal treatment after
forming the dielectric layer is performed in an oxidizing
atmosphere between about 400C and about 600C for between about 1
millsecond and about 60 minutes.
17. The method of claim 1, further comprising performing an anneal
treatment after forming the top electrode layer.
18. The method of claim 17, wherein the anneal treatment after
forming the top electrode layer is performed soon after forming the
top electrode layer.
19. A method for forming a capacitor stack, the method comprising:
forming a first bottom electrode layer above a surface of a
substrate, wherein the first bottom electrode layer comprises a
conductive metal nitride material; forming a second bottom
electrode layer above the first bottom electrode layer, wherein the
second bottom electrode layer comprises a conductive metal oxide
material; annealing the first and second bottom electrode layers;
forming a dielectric layer above the second bottom electrode layer,
wherein the dielectric layer comprises a metal oxide material;
annealing the dielectric layer; forming an oxygen-rich metal oxide
layer above the dielectric layer; forming a top electrode layer
above the oxygen-rich metal oxide layer, wherein the top electrode
layer comprises a conductive metal nitride material; and annealing
the oxygen-rich metal oxide layer so that at least a portion of the
oxygen-rich metal oxide layer is converted to a stoichiometric
metal oxide compound.
20. The method of claim 19, wherein the first bottom electrode
layer comprises titanium nitride, the second bottom electrode layer
comprises molybdenum oxide, the dielectric layer comprises titanium
oxide, the oxygen-rich metal oxide layer comprises molybdenum
oxide, and the top electrode layer comprises titanium nitride.
Description
[0001] This document relates to the subject matter of a joint
research agreement between Intermolecular, Inc. and Elpida Memory,
Inc.
TECHNICAL FIELD
[0002] The present disclosure relates generally to the field of
dynamic random access memory (DRAM), and more particularly to
methods of forming a capacitor stack for improved DRAM
performance.
BACKGROUND
[0003] Dynamic Random Access Memory utilizes capacitors to store
bits of information within an integrated circuit. A capacitor is
formed by placing a dielectric material between two electrodes
formed from conductive materials. A capacitor's ability to hold
electrical charge (i.e., capacitance) is a function of the surface
area of the capacitor plates A, the distance between the capacitor
plates d, and the relative dielectric constant or k-value of the
dielectric material. The capacitance is given by:
C = .kappa. o A d ( Eqn . 1 ) ##EQU00001##
where .di-elect cons..sub.0 represents the vacuum permittivity.
[0004] The dielectric constant is a measure of a material's
polarizability. Therefore, the higher the dielectric constant of a
material, the more electrical charge the capacitor can hold.
Therefore, for a given desired capacitance, if the k-value of the
dielectric is increased, the area of the capacitor can be decreased
to maintain the same cell capacitance. Reducing the size of
capacitors within the device is important for the miniaturization
of integrated circuits. This allows the packing of millions
(mega-bit (Mb)) or billions (giga-bit (Gb)) of memory cells into a
single semiconductor device. The goal is to maintain a large cell
capacitance (generally .about.10 to 25 fF) and a low leakage
current density (generally <10.sup.-7 A cm.sup.-2). The physical
thickness of the dielectric layers in DRAM capacitors cannot be
reduced without limit because leakage current caused by tunneling
mechanisms exponentially increases as the thickness of the
dielectric layer decreases.
[0005] Traditionally, SiO.sub.2 has been used as the dielectric
material and semiconducting materials
(semiconductor-insulator-semiconductor [SIS] cell designs) have
been used as the electrodes. The cell capacitance was maintained by
increasing the area of the capacitor using very complex capacitor
morphologies while also decreasing the thickness of the SiO.sub.2
dielectric layer. Increases of the leakage current above the
desired specifications have demanded the development of new
capacitor geometries, new electrode materials, and new dielectric
materials. Cell designs have migrated to
metal-insulator-semiconductor (MIS) and now to
metal-insulator-metal (MIM) cell designs for higher
performance.
[0006] Typically, DRAM devices at technology nodes of 80 nm and
below use MIM capacitors wherein the electrode materials are
metals. These electrode materials generally have higher
conductivities than the semiconductor electrode materials, higher
work functions, exhibit improved stability over the semiconductor
electrode materials, and exhibit reduced depletion effects. The
electrode materials must have high conductivity to ensure fast
device speeds. Representative examples of electrode materials for
MIM capacitors are metals, conductive metal oxides, conductive
metal silicides, conductive metal nitrides (i.e. titanium nitride),
or combinations thereof. MIM capacitors in these DRAM applications
utilize insulating materials having a dielectric constant, or
k-value, significantly higher than that of SiO.sub.2 (k=3.9). For
DRAM capacitors, the goal is to utilize dielectric materials with
k-values greater than about 40. Such materials are generally
classified as high-k materials. Representative examples of high-k
materials for MIM capacitors are non-conducting metal oxides,
non-conducting metal nitrides, non-conducting metal silicates or
combinations thereof. These dielectric materials may also include
additional dopant materials.
[0007] A figure of merit in DRAM technology is the electrical
performance of the dielectric material as compared to SiO.sub.2
known as the Equivalent Oxide Thickness (EOT). A high-k material's
EOT is calculated using a normalized measure of silicon dioxide
(SiO.sub.2 k=3.9) as a reference, given by:
E O T = 3.9 .kappa. d ( Eqn . 2 ) ##EQU00002##
where d represents the physical thickness of the capacitor
dielectric.
[0008] As DRAM technologies scale below the 40 nm technology node,
manufacturers must reduce the EOT of the high-k dielectric films in
MIM capacitors in order to increase charge storage capacity. The
goal is to utilize dielectric materials that exhibit an EOT of less
than about 0.8 nm while maintaining a physical thickness of about
5-20 nm.
[0009] There is a need to develop processes that allow the
formation of a metal oxide-based electrode material that can serve
as a template for the high-k phases of subsequently deposited
dielectric layers, that contributes to lower leakage current, and
has low resistivity, which contributes to higher device speed and
lower power usage.
SUMMARY
[0010] The following summary of the disclosure is included in order
to provide a basic understanding of some aspects and features of
the invention. This summary is not an extensive overview of the
invention and as such it is not intended to particularly identify
key or critical elements of the invention or to delineate the scope
of the invention. Its sole purpose is to present some concepts of
the invention in a simplified form as a prelude to the more
detailed description that is presented below.
[0011] In some embodiments, a first bottom electrode layer includes
a conductive metal nitride material. In some embodiments, the
conductive metal nitride material includes one of titanium nitride,
titanium aluminum nitride, titanium silicon nitride, tantalum
nitride, tantalum aluminum nitride, or tantalum silicon nitride. In
some embodiments, a second bottom electrode layer includes a
conductive metal oxide material. In some embodiments, the
conductive metal oxide material includes molybdenum oxide. In some
embodiments, an oxygen-rich metal oxide layer is deposited above a
dielectric layer. The oxygen-rich metal oxide layer can serve as a
source of oxygen to ensure that the concentration of oxygen
vacancies in the dielectric layer does not increase during
subsequent heat treatments. In some embodiments, a third top
electrode layer includes a conductive metal oxide material. In some
embodiments, the conductive metal oxide material includes
molybdenum oxide. In some embodiments, a fourth top electrode layer
includes a conductive metal nitride material. In some embodiments,
the conductive metal nitride material includes one of titanium
nitride, titanium aluminum nitride, titanium silicon nitride,
tantalum nitride, tantalum aluminum nitride, or tantalum silicon
nitride.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures. The drawings are not to scale and
the relative dimensions of various elements in the drawings are
depicted schematically and not necessarily to scale.
[0013] The techniques of the present invention can readily be
understood by considering the following detailed description in
conjunction with the accompanying drawings, in which:
[0014] FIG. 1 illustrates a flow chart illustrating a method for
fabricating a DRAM capacitor stack in accordance with some
embodiments of the present invention.
[0015] FIG. 2 illustrates a simplified cross-sectional view of a
DRAM capacitor stack fabricated in accordance with some
embodiments.
[0016] FIG. 3 illustrates a flow chart illustrating a method for
fabricating a DRAM capacitor stack in accordance with some
embodiments of the present invention.
[0017] FIG. 4 illustrates a simplified cross-sectional view of a
DRAM capacitor stack fabricated in accordance with some
embodiments.
[0018] FIG. 5 illustrates a flow chart illustrating a method for
fabricating a DRAM capacitor stack in accordance with some
embodiments of the present invention.
[0019] FIG. 6 illustrates a simplified cross-sectional view of a
DRAM capacitor stack fabricated in accordance with some
embodiments.
[0020] FIG. 7 presents data for the % increase in sheet resistance
for several materials according to some embodiments.
[0021] FIG. 8 presents x-ray diffraction (XRD) data for MoO.sub.x
materials according to some embodiments.
[0022] FIG. 9 illustrates a simplified cross-sectional view of a
DRAM memory cell fabricated in accordance with some embodiments of
the present invention.
[0023] FIG. 10 illustrates a simplified cross-sectional view of a
DRAM memory cell fabricated in accordance with some embodiments of
the present invention.
[0024] FIG. 11 illustrates a simplified cross-sectional view of a
DRAM memory cell fabricated in accordance with some embodiments of
the present invention.
DETAILED DESCRIPTION
[0025] A detailed description of one or more embodiments is
provided below along with accompanying figures. The detailed
description is provided in connection with such embodiments, but is
not limited to any particular example. The scope is limited only by
the claims and numerous alternatives, modifications, and
equivalents are encompassed. Numerous specific details are set
forth in the following description in order to provide a thorough
understanding. These details are provided for the purpose of
example and the described techniques may be practiced according to
the claims without some or all of these specific details. For the
purpose of clarity, technical material that is known in the
technical fields related to the embodiments has not been described
in detail to avoid unnecessarily obscuring the description.
[0026] It must be noted that as used herein and in the claims, the
singular forms "a," "an," and "the" include plural referents unless
the context clearly dictates otherwise. Thus, for example,
reference to "a layer" includes two or more layers, and so
forth.
[0027] Where a range of values is provided, it is understood that
each intervening value, to the tenth of the unit of the lower limit
unless the context clearly dictates otherwise, between the upper
and lower limit of that range, and any other stated or intervening
value in that stated range, is encompassed within the invention.
The upper and lower limits of these smaller ranges may
independently be included in the smaller ranges, and are also
encompassed within the invention, subject to any specifically
excluded limit in the stated range. Where the stated range includes
one or both of the limits, ranges excluding either or both of those
included limits are also included in the invention. Where the
modifier "about" or "approximately" is used, the stated quantity
can vary by up to 10%. Where the modifier "substantially equal to"
or "substantially the same" is used, the two quantities may vary
from each other by no more than 5%.
[0028] The term "horizontal" as used herein will be understood to
be defined as a plane parallel to the plane or surface of the
substrate, regardless of the orientation of the substrate. The term
"vertical" will refer to a direction perpendicular to the
horizontal as previously defined. Terms such as "above", "below",
"bottom", "top", "side" (e.g. sidewall), "higher", "lower",
"upper", "over", and "under", are defined with respect to the
horizontal plane. The term "on" means there is direct contact
between the elements. The term "above" will allow for intervening
elements.
[0029] The discussion herein will use a simple capacitor stack as
an illustration. The capacitor stack will include a first electrode
layer (sometimes called a bottom electrode layer), a dielectric
layer, and a second electrode layer (sometimes called a top
electrode layer). Those skilled in the art will understand that
each of the first electrode layer, dielectric layer, and second
electrode layer may include multiple layers and multiple materials.
In some embodiments, an additional layer will be inserted between
the first electrode layer and the dielectric layer. As used herein,
this layer will be labeled a "flash" layer. In some embodiments, an
additional layer will be inserted between the dielectric layer and
the second electrode layer. As used herein, this layer will be
labeled a "capping" layer. The terms "first", "bottom", "second",
"top", "flash", "capping", etc. are included for convenience and to
assist in the description of the capacitor stack and are not meant
to be limiting.
[0030] As used herein, a material (e.g. a dielectric material or an
electrode material) will be considered to be "crystalline" if it
exhibits greater than or equal to 30% crystallinity as measured by
a technique such as x-ray diffraction (XRD).
[0031] As used herein, a "dopant" is a minor constituent of a layer
or material that is purposely added. As used herein, the dopant may
be electrically active or not electrically active. The definition
excludes residues and impurities such as carbon, etc. that may be
present in the material due to inefficiencies of the process or
impurities in the precursor materials.
[0032] Those skilled in the art will appreciate that each of the
layers discussed herein and used in the DRAM MIM capacitor may be
formed using any common formation technique such as atomic layer
deposition (ALD), plasma enhanced atomic layer deposition (PE-ALD),
atomic vapor deposition (AVD), ultraviolet assisted atomic layer
deposition (UV-ALD), chemical vapor deposition (CVD), plasma
enhanced chemical vapor deposition (PECVD), or physical vapor
deposition (PVD). Generally, because of the complex morphology of
the DRAM capacitor structure, ALD, PE-ALD, AVD, or CVD are
preferred methods of formation. However, any of these techniques
are suitable for forming each of the various layers discussed
herein. Those skilled in the art will appreciate that the teachings
described herein are not limited by the technology used for the
deposition process.
[0033] In FIGS. 2, 4, 6, and 9-11, a capacitor stack is illustrated
using a simple planar structure. Those skilled in the art will
appreciate that the description and teachings herein can be readily
applied to any simple or complex capacitor morphology. The drawings
are for illustrative purposes only and do not limit the application
of the present disclosure.
[0034] One class of high-k dielectric materials possessing the
characteristics required for implementation in advanced DRAM
capacitors includes high-k metal oxide materials. Titanium oxide
and zirconium oxide are two metal oxide dielectric materials which
display significant promise in terms of serving as high-k
dielectric materials for implementation in DRAM capacitors. Other
metal oxide high-k dielectric materials that have attracted
attention include aluminum oxide, barium-strontium-titanate (BST),
erbium oxide, hafnium oxide, hafnium silicate, lanthanum oxide,
niobium oxide, lead-zirconium-titanate (PZT), a bilayer of silicon
oxide and silicon nitride, silicon oxy-nitride, strontium titanate
(STO), tantalum oxide, titanium oxide, zirconium oxide, etc.
[0035] The dielectric constant of a dielectric material may be
dependent upon the crystalline phase(s) of the material. For
example, in the case of titanium oxide (specifically TiO.sub.2),
the anatase crystalline phase of TiO.sub.2 has a dielectric
constant of approximately 40, while the rutile crystalline phase of
TiO.sub.2 can have a dielectric constant of approximately >80.
Due to the higher k-value of the rutile-phase, it is desirable to
produce TiO.sub.2 based DRAM capacitors with the TiO.sub.2 in the
rutile-phase. The relative amounts of the anatase phase and the
rutile phase can be determined from x-ray diffraction (XRD). From
Eqn. 1 above, a TiO.sub.2 material in the rutile-phase could be
physically thicker and maintain the desired capacitance. The
increased physical thickness is important for lowering the leakage
current of the capacitor. The anatase phase will transition to the
rutile phase at high temperatures (>8000). However, high
temperature processes are undesirable in the manufacture of DRAM
devices. Similarly, the cubic and tetragonal phases of ZrO.sub.2
have a higher-k value than the monoclinic phase. So, it is
desirable to produce ZrO.sub.2 based DRAM capacitors with the
ZrO.sub.2 in the cubic or tetragonal phase.
[0036] The crystal phase of an adjacent material can be used to
influence the growth of a specific crystal phase of a material if
their crystal structures are similar and their lattice constants
are similar. This technique is well known in technologies such as
epitaxial growth. The same concepts have been extended to the
growth of thin films where the adjacent material can be used as a
"template" to encourage the growth of a desired crystalline phase
over other competing crystal phases.
[0037] Generally, as the dielectric constant of a material
increases, the band gap of the material decreases. This leads to
high leakage current in the device. As a result, without the
utilization of countervailing measures, capacitor stacks
implementing high-k dielectric materials may experience large
leakage currents. High work function electrodes (e.g., electrodes
having a work function of greater than 5.0 eV) may be utilized in
order to counter the effects of implementing a reduced band gap
high-k dielectric material within the DRAM capacitor. Metals, such
as platinum, gold, ruthenium, and ruthenium oxide are examples of
high work function electrode materials suitable for inhibiting
device leakage in a DRAM capacitor having a high-k dielectric
material. The noble metal systems, however, are prohibitively
expensive when employed in a mass production context. Moreover,
electrodes fabricated from noble metals often suffer from poor
manufacturing qualities, such as surface roughness and poor
adhesion, and form a contamination risk in the fab.
[0038] Additionally, DRAM capacitor stacks may undergo various
refinement process steps after fabrication. These refinement
processes may include post-fabrication chemical and thermal
processing (i.e., oxidation or reduction). For instance, after
initial DRAM capacitor stack fabrication, a number of high
temperature (up to about 60.degree. C.) processes may be applied to
complete the device fabrication. During these subsequent process
steps, the DRAM capacitor materials must remain chemically,
physically, and structurally stable. They must maintain the
structural, compositional, physical, and electrical properties that
have been developed. Furthermore, they should not undergo
significant interaction or reaction which may degrade the
performance of the DRAM capacitor.
[0039] Conductive metal oxides, conductive metal silicides,
conductive metal carbides, conductive metal nitrides, or
combinations thereof comprise other classes of materials that may
be suitable as DRAM capacitor electrodes. Generally, transition
metals and their conductive binary compounds form good candidates
as electrode materials. The transition metals exist in several
oxidation states. Therefore, a wide variety of compounds are
possible. Conductive metal nitrides such as titanium nitride,
tantalum nitride, tungsten nitride, etc. have attracted interest as
DRAM capacitor electrodes with titanium nitride being the most
popular. Different compounds may have different crystal structures,
electrical properties, etc. It is important to utilize the proper
compound for the desired application.
[0040] In one example, molybdenum has several binary oxides of
which MoO.sub.2 and MoO.sub.3 are two examples. These two oxides of
molybdenum have different properties. MoO.sub.2 is conductive and
has shown great promise as an electrode material in DRAM
capacitors. MoO.sub.2 has a distorted rutile crystal structure and
can serve as an acceptable template to promote the deposition of
the rutile-phase of titanium oxide as discussed above. MoO.sub.2
also has a high work function (can be >5.0 eV depending on
process history) which helps to minimize the leakage current of the
DRAM device. However, oxygen-rich phases (MoO.sub.2+x) of MoO.sub.2
degrade the performance of the MoO.sub.2 electrode material because
they act more like insulators and have crystal structures that do
not promote the formation of the rutile-phase of titanium oxide.
For example, MoO.sub.3 (the most oxygen-rich phase) is a dielectric
material and has an orthorhombic crystal structure.
[0041] Generally, a deposited thin film may be amorphous,
crystalline, or a mixture thereof. Furthermore, several different
crystalline phases may exist. Therefore, processes (both deposition
and post-treatment) must be developed to maximize the formation of
crystalline MoO.sub.2 and to minimize the presence of MoO.sub.2+x
phases. Deposition processes and post-treatment processes in an
inert or reducing atmosphere have been developed that allow
crystalline MoO.sub.2 to be used as the first electrode material
(i.e. bottom electrode) in MIM DRAM capacitors with TiO.sub.2 or
doped-TiO.sub.2 high-k dielectric materials. Examples of the
post-treatment process are further described in U.S. application
Ser. No. 13/084,666 filed on Apr. 12, 2011, entitled "METHOD FOR
FABRICATING A DRAM CAPACITOR", (US Publication 2012/0262835), which
is incorporated herein by reference for all purposes. Other
conductive metal oxides that may be used as a template for the
rutile phase of TiO.sub.2 include the conductive compounds of
chromium oxide, cobalt oxide, iridium oxide, manganese oxide,
nickel oxide, ruthenium oxide, tin oxide, or tungsten oxide.
[0042] The use of MoO.sub.2 as a first electrode material has a
number of additional issues. Although the work function can be
around 5.0 eV, this is not high enough to minimize the leakage
current to meet the specifications of some advanced devices.
Additionally, the resistivity of MoO.sub.2 is high (1000
.mu..OMEGA. cm). This impacts the speed and power usage of the
device.
[0043] FIG. 1 describes a method, 100, for fabricating a DRAM
capacitor stack. The initial step, 102, includes forming a first
bottom electrode layer above a substrate, wherein the first bottom
electrode layer comprises a metal element. Examples of suitable
electrode materials include metals, conductive metal oxides,
conductive metal silicides, conductive metal nitrides, and
combinations thereof. Two particularly interesting classes of
materials are the conductive metal oxides and the conductive metal
nitrides. The purpose of the first bottom electrode layer is to
serve as a primary conductor. Examples of suitable materials for
the first bottom electrode layer include titanium nitride, titanium
aluminum nitride, titanium silicon nitride, tantalum nitride,
tantalum aluminum nitride, and tantalum silicon nitride or
combinations thereof.
[0044] The next step, 104, includes forming a second bottom
electrode layer above the first bottom electrode layer, wherein the
second bottom electrode layer comprises a metal element. Examples
of suitable electrode materials include metals, conductive metal
oxides, conductive metal silicides, conductive metal nitrides, and
combinations thereof. Two particularly interesting classes of
materials are the conductive metal oxides and the conductive metal
nitrides. The purpose of the second bottom electrode layer is to
promote a desired crystallographic structure and orientation of a
subsequently deposited dielectric layer. As discussed previously,
the k-value of a dielectric material may vary as a function of its
crystallographic structure and orientation. Examples of suitable
materials for the second bottom electrode layer include molybdenum
oxide, chromium oxide, cobalt oxide, iridium oxide, manganese
oxide, nickel oxide, ruthenium oxide, tin oxide, or tungsten oxide.
The first bottom electrode layer and the second bottom electrode
layer can then be subjected to an annealing process (not shown).
The annealing step serves to crystallize the second bottom
electrode layer.
[0045] The next step, 106, includes forming a dielectric layer
above the second bottom electrode layer. Optionally, the dielectric
layer can then be subjected to a post dielectric anneal (PDA)
treatment (not shown). The PDA step serves to crystallize the
dielectric material and fill oxygen vacancies.
[0046] The next step, 108, includes forming a fourth top electrode
layer above the dielectric layer to form a capacitor stack, wherein
the fourth top electrode layer comprises a metal element. Examples
of suitable fourth top electrode materials include metals,
conductive metal oxides, conductive metal silicides, conductive
metal nitrides, and combinations thereof. Examples of suitable
materials for the fourth top electrode layer include titanium
nitride, titanium aluminum nitride, titanium silicon nitride,
tantalum nitride, tantalum aluminum nitride, or tantalum silicon
nitride, or combinations thereof. Optionally, the capacitor stack
can then be subjected to a post metallization anneal (PMA)
treatment process (not shown). In some embodiments, the PMA
treatment is performed soon (i.e. before further processing steps)
after the forming of the fourth top electrode layer. The PMA
treatments are typically performed in an inert gas (e.g. nitrogen
or argon) or in a dilute oxygen atmosphere (e.g. less than about
10% oxygen in nitrogen or argon). Preferably, the PMA treatments
are performed in an inert gas. Examples of the PDA and PMA
treatments are further described in U.S. patent application Ser.
No. 13/159,842, filed on Jun. 14, 2011, (US Publication
2012/0322220), which is herein incorporated by reference for all
purposes.
[0047] FIG. 2 illustrates a simple capacitor stack, 200, consistent
with some embodiments. Using the method as outlined in FIG. 1 and
described above, first bottom electrode layer, 204, is formed above
substrate, 202. Generally, the substrate has already received
several processing steps in the manufacture of a full DRAM device.
First bottom electrode layer, 204, can include one of metals,
conductive metal oxides, conductive metal nitrides, conductive
metal silicides, and combinations thereof. In some embodiments, the
first bottom electrode material is a conductive metal nitride.
Examples of suitable conductive metal nitrides include titanium
nitride, titanium aluminum nitride, titanium silicon nitride,
tantalum nitride, tantalum aluminum nitride, or tantalum silicon
nitride, nickel nitride, tungsten nitride, vanadium nitride,
molybdenum nitride, and cobalt nitride, or combinations
thereof.
[0048] In the next step, a second bottom electrode layer, 206, is
formed above the first bottom electrode layer, wherein the second
bottom electrode layer comprises a metal element. Examples of
suitable electrode materials include metals, conductive metal
oxides, conductive metal silicides, conductive metal nitrides, and
combinations thereof. Two particularly interesting classes of
materials are the conductive metal oxides and the conductive metal
nitrides. Examples of suitable materials for the second bottom
electrode layer include molybdenum oxide, chromium oxide, cobalt
oxide, iridium oxide, manganese oxide, nickel oxide, ruthenium
oxide, tin oxide, or tungsten oxide.
[0049] In the next step, dielectric layer, 208, would then be
formed above the second bottom electrode layer, 206. A wide variety
of dielectric materials have been targeted for use in DRAM
capacitors. Examples of suitable dielectric materials include
aluminum oxide, barium-strontium-titanate (BST), erbium oxide,
hafnium oxide, lanthanum oxide, niobium oxide,
lead-zirconium-titanate (PZT), a bilayer of silicon oxide and
silicon nitride, silicon oxy-nitride, strontium titanate (STO),
tantalum oxide, titanium oxide, zirconium oxide, or doped versions
of the same. These dielectric materials may be formed as a single
layer or may be formed as a hybrid or nanolaminate structure. In
some embodiments, the dielectric material is titanium oxide. In
some embodiments, the dielectric material is doped titanium oxide.
Typical dopants for titanium oxide include Al, Ce, Co, Er, Ga, Gd,
Ge, Hf, In, La, Lu, Mg, Mn, Nd, Pr, Sc, Si, Sn, Sr, Y, Zr, or
combinations thereof.
[0050] In the next step, the fourth top electrode layer, 210, is
formed above dielectric layer, 208, to form a capacitor stack. The
fourth top electrode layer can include at least one of metals,
conductive metal oxides, conductive metal nitrides, conductive
metal silicides, conductive metal carbides, and combinations
thereof. Examples of suitable conductive metal nitrides include
titanium nitride, titanium aluminum nitride, titanium silicon
nitride, tantalum nitride, tantalum aluminum nitride, or tantalum
silicon nitride, nickel nitride, tungsten nitride, vanadium
nitride, molybdenum nitride, and cobalt nitride, or combinations
thereof. Typically, the capacitor stack would then be subjected to
a PMA treatment. In some embodiments, the PMA treatment is
performed soon (i.e. before further processing steps) after the
forming of the fourth top electrode layer.
[0051] In some embodiments, a DRAM MIM capacitor stack includes a
first bottom electrode layer including between about 5 nm and about
10 nm of a conductive metal nitride formed on a substrate. Examples
of suitable conductive metal nitrides include titanium nitride,
titanium aluminum nitride, titanium silicon nitride, tantalum
nitride, tantalum aluminum nitride, or tantalum silicon nitride,
nickel nitride, tungsten nitride, vanadium nitride, molybdenum
nitride, and cobalt nitride, or combinations thereof. The
conductive metal nitride first bottom electrode material is formed
at a process temperature between about 150C and 400C using an ALD
or CVD process technology. Optionally, the substrate with the first
bottom electrode layer is then treated as discussed previously.
[0052] In some embodiments, a second bottom electrode layer
including between about 5 nm and about 10 nm of molybdenum oxide is
formed above the first bottom electrode layer. The molybdenum oxide
second bottom electrode layer is formed at a process temperature
between about 150C and 400C using an ALD process technology.
Optionally, the substrate with the first bottom electrode layer and
the second bottom electrode layer is then annealed in an inert
(e.g. argon or nitrogen) or a reducing atmosphere for between about
1 millisecond and about 60 minutes. In some embodiments, the
reducing atmosphere includes between about 1% and about 20% H.sub.2
in N.sub.2 and advantageously between about 5% and about 10%
H.sub.2 in N.sub.2 between 400 and 520C.
[0053] A dielectric layer would then be formed on the annealed
second bottom electrode layer. A wide variety of dielectric
materials have been targeted for use in DRAM capacitors. Examples
of suitable dielectric materials include aluminum oxide,
barium-strontium-titanate (BST), erbium oxide, hafnium oxide,
lanthanum oxide, niobium oxide, lead-zirconium-titanate (PZT), a
bilayer of silicon oxide and silicon nitride, silicon oxy-nitride,
strontium titanate (STO), tantalum oxide, titanium oxide, zirconium
oxide, or doped versions of the same. These dielectric materials
may be formed as a single layer or may be formed as a hybrid or
nanolaminate structure. Typical dopants for titanium oxide include
Al, Ce, Co, Er, Ga, Gd, Ge, Hf, In, La, Lu, Mg, Mn, Nd, Pr, Sc, Si,
Sn, Sr, Y, Zr, or combinations thereof. Typically, the dielectric
layer is subjected to a PDA treatment before the formation of the
fourth top electrode layer as discussed previously. A dielectric
material of interest is titanium oxide doped with aluminum (e.g. as
aluminum oxide) to between about 5 atomic % and about 15 atomic %
Al as calculated by (Al/(Al+Ti)).
[0054] In a specific example, the dielectric layer comprises
between about 6 nm to about 10 nm of TiO.sub.2 wherein at least 30%
of the TiO.sub.2 is present in the rutile phase. Generally, the
TiO.sub.2 dielectric layer may either be a single film or may
comprise a nanolaminate. Advantageously, the TiO.sub.2 material is
doped with Al at a concentration between about 5 atomic % and about
15 atomic % Al as calculated by (Al/(Al+Ti)). The TiO.sub.2
dielectric layer is formed at a process temperature between about
200C and 350C using an ALD process technology. The substrate with
the first electrode and dielectric layer is then annealed in an
oxidizing atmosphere comprising between about 0% O.sub.2 to about
100% O.sub.2 in N.sub.2 and advantageously between about 0% O.sub.2
to about 20% O.sub.2 in N.sub.2 at temperatures between about 400C
to about 600C for between about 1 millisecond to about 60
minutes.
[0055] In the next step, the fourth top electrode layer is formed
above the dielectric layer to complete the formation of the
capacitor stack. The fourth top electrode layer may include one of,
metals, metal alloys, conductive metal oxides, conductive metal
nitrides, conductive metal silicides, or combinations thereof, etc.
In some embodiments, the fourth top electrode layer is a noble
metal such as platinum or ruthenium. In some embodiments, the
fourth top electrode layer is a conductive metal nitride. Examples
of suitable conductive metal nitrides include titanium nitride,
titanium aluminum nitride, titanium silicon nitride, tantalum
nitride, tantalum aluminum nitride, or tantalum silicon nitride,
nickel nitride, tungsten nitride, vanadium nitride, molybdenum
nitride, and cobalt nitride, or combinations thereof. The capacitor
stack may receive a PMA treatment as discussed previously. In some
embodiments, the PMA treatment is performed soon (i.e. before
further processing steps) after the forming of the fourth top
electrode layer.
[0056] In some embodiments, the first bottom electrode layer
includes titanium nitride and the second bottom electrode layer
includes molybdenum oxide. Optionally, the first bottom electrode
layer and the second bottom electrode layer are subjected to an
annealing treatment before the deposition of a subsequent
dielectric layer. In some embodiments, the dielectric layer
includes doped titanium oxide. Optionally, the dielectric layer is
subjected to an annealing treatment before the deposition of a
subsequent fourth top electrode layer. In some embodiments, the
fourth top electrode layer includes titanium nitride. Optionally,
the capacitor stack may be subjected to a PMA treatment. In some
embodiments, the PMA treatment is performed soon (i.e. before
further processing steps) after the forming of the fourth top
electrode layer.
[0057] In some embodiments, the first bottom electrode layer
includes titanium aluminum nitride and the second bottom electrode
layer includes molybdenum oxide. Optionally, the first bottom
electrode layer and the second bottom electrode layer are subjected
to an annealing treatment before the deposition of a subsequent
dielectric layer. In some embodiments, the dielectric layer
includes doped titanium oxide. Optionally, the dielectric layer is
subjected to an annealing treatment before the deposition of a
subsequent fourth top electrode layer. In some embodiments, the
fourth top electrode layer includes titanium aluminum nitride.
Optionally, the capacitor stack may be subjected to a PMA
treatment. In some embodiments, the PMA treatment is performed soon
(i.e. before further processing steps) after the forming of the
fourth top electrode layer.
[0058] In some embodiments, the first bottom electrode layer
includes titanium silicon nitride and the second bottom electrode
layer includes molybdenum oxide. Optionally, the first bottom
electrode layer and the second bottom electrode layer are subjected
to an annealing treatment before the deposition of a subsequent
dielectric layer. In some embodiments, the dielectric layer
includes doped titanium oxide. Optionally, the dielectric layer is
subjected to an annealing treatment before the deposition of a
subsequent fourth top electrode layer. In some embodiments, the
fourth top electrode layer includes titanium silicon nitride.
Optionally, the capacitor stack may be subjected to a PMA
treatment. In some embodiments, the PMA treatment is performed soon
(i.e. before further processing steps) after the forming of the
fourth top electrode layer.
[0059] In some embodiments, the first bottom electrode layer
includes tantalum nitride and the second bottom electrode layer
includes molybdenum oxide. Optionally, the first bottom electrode
layer and the second bottom electrode layer are subjected to an
annealing treatment before the deposition of a subsequent
dielectric layer. In some embodiments, the dielectric layer
includes doped titanium oxide. Optionally, the dielectric layer is
subjected to an annealing treatment before the deposition of a
subsequent fourth top electrode layer. In some embodiments, the
fourth top electrode layer includes tantalum nitride. Optionally,
the capacitor stack may be subjected to a PMA treatment. In some
embodiments, the PMA treatment is performed soon (i.e. before
further processing steps) after the forming of the fourth top
electrode layer.
[0060] In some embodiments, the first bottom electrode layer
includes tantalum aluminum nitride and the second bottom electrode
layer includes molybdenum oxide. Optionally, the first bottom
electrode layer and the second bottom electrode layer are subjected
to an annealing treatment before the deposition of a subsequent
dielectric layer. In some embodiments, the dielectric layer
includes doped titanium oxide. Optionally, the dielectric layer is
subjected to an annealing treatment before the deposition of a
subsequent fourth top electrode layer. In some embodiments, the
fourth top electrode layer includes tantalum aluminum nitride.
Optionally, the capacitor stack may be subjected to a PMA
treatment. In some embodiments, the PMA treatment is performed soon
(i.e. before further processing steps) after the forming of the
fourth top electrode layer.
[0061] In some embodiments, the first bottom electrode layer
includes tantalum silicon nitride and the second bottom electrode
layer includes molybdenum oxide. Optionally, the first bottom
electrode layer and the second bottom electrode layer are subjected
to an annealing treatment before the deposition of a subsequent
dielectric layer. In some embodiments, the dielectric layer
includes doped titanium oxide. Optionally, the dielectric layer is
subjected to an annealing treatment before the deposition of a
subsequent fourth top electrode layer. In some embodiments, the
fourth top electrode layer includes tantalum silicon nitride.
Optionally, the capacitor stack may be subjected to a PMA
treatment. In some embodiments, the PMA treatment is performed soon
(i.e. before further processing steps) after the forming of the
fourth top electrode layer.
[0062] FIG. 3 describes a method, 300, for fabricating a DRAM
capacitor stack. The initial step, 302, includes forming a first
bottom electrode layer above a substrate, wherein the first bottom
electrode layer comprises a metal element. Examples of suitable
electrode materials include metals, conductive metal oxides,
conductive metal silicides, conductive metal nitrides, and
combinations thereof. Two particularly interesting classes of
materials are the conductive metal oxides and the conductive metal
nitrides. The purpose of the first bottom electrode layer is to
serve as a primary conductor. Examples of suitable materials for
the first bottom electrode layer include titanium nitride, titanium
aluminum nitride, titanium silicon nitride, tantalum nitride,
tantalum aluminum nitride, or tantalum silicon nitride or
combinations thereof.
[0063] The next step, 304, includes forming a second bottom
electrode layer above the first bottom electrode layer, wherein the
second bottom electrode layer comprises a metal element. Examples
of suitable electrode materials include metals, conductive metal
oxides, conductive metal silicides, conductive metal nitrides, and
combinations thereof. Two particularly interesting classes of
materials are the conductive metal oxides and the conductive metal
nitrides. The purpose of the second bottom electrode layer is to
promote a desired crystallographic orientation of a subsequently
deposited dielectric layer. As discussed previously, the k-value of
a dielectric material may vary as a function of its
crystallographic orientation. Examples of suitable materials for
the second bottom electrode layer include molybdenum oxide,
chromium oxide, cobalt oxide, iridium oxide, manganese oxide,
nickel oxide, ruthenium oxide, tin oxide, or tungsten oxide. The
first bottom electrode layer and the second bottom electrode layer
can then be subjected to an annealing process (not shown). The
annealing step serves to crystallize the bottom electrode
layers.
[0064] The next step, 306, includes forming a dielectric layer
above the second bottom electrode layer. Optionally, the dielectric
layer can then be subjected to a post dielectric anneal (PDA)
treatment (not shown). The PDA step serves to crystallize the
dielectric material and fill oxygen vacancies.
[0065] The next step, 308, includes forming an oxygen-rich metal
oxide layer above the dielectric layer. As used herein, an
oxygen-rich metal oxide layer will be understood to contain more
oxygen than at least one of the stoichiometric metal oxide
compounds of that metal. As an example, if the stoichiometric
formula of a metal oxide is MO.sub.2 (where M stands for the metal
component), then an oxygen-rich compound would be given
MO.sub.(2+x). Those skilled in the art will understand that the
same metal may have additional metal oxide compounds such as
MO.sub.3. As used herein, the MO.sub.(2+x) layer would still be
considered oxygen-rich since it has more oxygen than the MO.sub.2
compound. The oxygen-rich metal oxide layer can serve as a source
of oxygen to ensure that the concentration of oxygen vacancies in
the dielectric layer does not increase during subsequent heat
treatments. At least a portion of oxygen-rich metal layer is
converted to a stoichiometric metal oxide compound by supplying
oxygen to the dielectric layer during the heat treatment.
[0066] The next step, 310, includes forming a fourth top electrode
layer above the oxygen-rich metal oxide layer to form a capacitor
stack, wherein the fourth top electrode layer comprises a metal
element. Examples of suitable fourth top electrode materials
include metals, conductive metal oxides, conductive metal
silicides, conductive metal nitrides, and combinations thereof.
Examples of suitable conductive metal nitrides include titanium
nitride, titanium aluminum nitride, titanium silicon nitride,
tantalum nitride, tantalum aluminum nitride, or tantalum silicon
nitride, nickel nitride, tungsten nitride, vanadium nitride,
molybdenum nitride, and cobalt nitride, or combinations thereof.
Optionally, the capacitor stack can then be subjected to PMA
treatment process (not shown) as discussed previously. In some
embodiments, the PMA treatment is performed soon (i.e. before
further processing steps) after the forming of the fourth top
electrode layer.
[0067] FIG. 4 illustrates a simple capacitor stack, 400, consistent
with some embodiments. Using the method as outlined in FIG. 3 and
described above, first bottom electrode layer, 404, is formed above
substrate, 402. Generally, the substrate has already received
several processing steps in the manufacture of a full DRAM device.
First bottom electrode layer, 404, can include one of metals,
conductive metal oxides, conductive metal nitrides, conductive
metal silicides, and combinations thereof. In some embodiments, the
first bottom electrode material is a conductive metal nitride.
Examples of suitable conductive metal nitrides include titanium
nitride, titanium aluminum nitride, titanium silicon nitride,
tantalum nitride, tantalum aluminum nitride, or tantalum silicon
nitride, nickel nitride, tungsten nitride, vanadium nitride,
molybdenum nitride, and cobalt nitride, or combinations
thereof.
[0068] In the next step, a second bottom electrode layer, 406, is
formed above the first bottom electrode layer, wherein the second
bottom electrode layer comprises a metal element. Examples of
suitable electrode materials include metals, conductive metal
oxides, conductive metal silicides, conductive metal nitrides, and
combinations thereof. Two particularly interesting classes of
materials are the conductive metal oxides and the conductive metal
nitrides. Examples of suitable materials for the second bottom
electrode layer include molybdenum oxide, chromium oxide, cobalt
oxide, iridium oxide, manganese oxide, nickel oxide, ruthenium
oxide, tin oxide, or tungsten oxide.
[0069] In the next step, dielectric layer, 408, would then be
formed above the second bottom electrode layer, 406. A wide variety
of dielectric materials have been targeted for use in DRAM
capacitors. Examples of suitable dielectric materials include
aluminum oxide, barium-strontium-titanate (BST), erbium oxide,
hafnium oxide, lanthanum oxide, niobium oxide,
lead-zirconium-titanate (PZT), a bilayer of silicon oxide and
silicon nitride, silicon oxy-nitride, strontium titanate (STO),
tantalum oxide, titanium oxide, zirconium oxide, or doped versions
of the same. These dielectric materials may be formed as a single
layer or may be formed as a hybrid or nanolaminate structure. In
some embodiments, the dielectric material is titanium oxide. In
some embodiments, the dielectric material is doped titanium oxide.
Typical dopants for titanium oxide include Al, Ce, Co, Er, Ga, Gd,
Ge, Hf, In, La, Lu, Mg, Mn, Nd, Pr, Sc, Si, Sn, Sr, Y, Zr, or
combinations thereof.
[0070] In the next step, oxygen-rich metal oxide layer 410, would
then be formed above the dielectric layer, 408.
[0071] In the next step, the fourth top electrode layer, 412, is
formed above oxygen-rich metal oxide layer, 410, to form a
capacitor stack. The fourth top electrode layer can include at
least one of metals, conductive metal oxides, conductive metal
nitrides, conductive metal silicides, conductive metal carbides,
and combinations thereof. Examples of suitable conductive metal
nitrides include titanium nitride, titanium aluminum nitride,
titanium silicon nitride, tantalum nitride, tantalum aluminum
nitride, or tantalum silicon nitride, nickel nitride, tungsten
nitride, vanadium nitride, molybdenum nitride, and cobalt nitride,
or combinations thereof. Typically, the capacitor stack would then
be subjected to a PMA treatment. In some embodiments, the PMA
treatment is performed soon (i.e. before further processing steps)
after the forming of the fourth top electrode layer.
[0072] In some embodiments, a DRAM MIM capacitor stack includes a
first bottom electrode layer including between about 5 nm and about
10 nm of a conductive metal nitride formed on a substrate. Examples
of suitable conductive metal nitrides include titanium nitride,
titanium aluminum nitride, titanium silicon nitride, tantalum
nitride, tantalum aluminum nitride, or tantalum silicon nitride,
nickel nitride, tungsten nitride, vanadium nitride, molybdenum
nitride, and cobalt nitride, or combinations thereof. The
conductive metal nitride first bottom electrode material is formed
at a process temperature between about 150C and 400C using an ALD
or CVD process technology. Optionally, the substrate with the first
bottom electrode layer is then treated as discussed previously.
[0073] In some embodiments, a second bottom electrode layer
including between about 5 nm and about 10 nm of molybdenum oxide is
formed above the first bottom electrode layer. The molybdenum oxide
second bottom electrode layer is formed at a process temperature
between about 150C and 400C using an ALD process technology. The
substrate with the first bottom electrode layer and the second
bottom electrode layer is then annealed in an inert (e.g. argon or
nitrogen) or a reducing atmosphere for between about 1 millisecond
and about 60 minutes. In some embodiments, the reducing atmosphere
includes between about 1% and about 20% H.sub.2 in N.sub.2 and
advantageously between about 5% and about 10% H.sub.2 in N.sub.2
between 400 and 520C.
[0074] A dielectric layer would then be formed on the annealed
second bottom electrode layer. A wide variety of dielectric
materials have been targeted for use in DRAM capacitors. Examples
of suitable dielectric materials include aluminum oxide,
barium-strontium-titanate (BST), erbium oxide, hafnium oxide,
lanthanum oxide, niobium oxide, lead-zirconium-titanate (PZT), a
bilayer of silicon oxide and silicon nitride, silicon oxy-nitride,
strontium titanate (STO), tantalum oxide, titanium oxide, zirconium
oxide, or doped versions of the same. These dielectric materials
may be formed as a single layer or may be formed as a hybrid or
nanolaminate structure. Typically, the dielectric layer is
subjected to a PDA treatment before the formation of the fourth top
electrode layer as discussed previously. A dielectric material of
interest is titanium oxide doped with aluminum (e.g. as aluminum
oxide) to between about 5 atomic % and about 15 atomic % Al as
calculated by (Al/(Al+Ti)).
[0075] In a specific example, the dielectric layer comprises
between about 6 nm to about 10 nm of TiO.sub.2 wherein at least 30%
of the TiO.sub.2 is present in the rutile phase. Generally, the
TiO.sub.2 dielectric layer may either be a single film or may
comprise a nanolaminate. Advantageously, the TiO.sub.2 material is
doped with Al at a concentration between about 5 atomic % and about
15 atomic % Al as calculated by (Al/(Al+Ti)). The TiO.sub.2
dielectric layer is formed at a process temperature between about
200C and 350C using an ALD process technology. The substrate with
the first electrode and dielectric layer is then annealed in an
oxidizing atmosphere comprising between about 0% O.sub.2 to about
100% O.sub.2 in N.sub.2 and advantageously between about 0% O.sub.2
to about 20% O.sub.2 in N.sub.2 at temperatures between about 400C
to about 600C for between about 1 millisecond to about 60
minutes.
[0076] In the next step, an oxygen-rich metal oxide layer including
between about 0.5 nm and about 2.0 nm of molybdenum oxide is formed
above the dielectric layer. The molybdenum oxide oxygen-rich metal
oxide layer is formed at a process temperature between about 150C
and 400C using an ALD process technology. The molybdenum oxide
oxygen-rich metal oxide layer may be formed by extending the ozone
step time longer than the molybdenum precursor step time during the
ALD deposition process. The molybdenum oxide oxygen-rich metal
oxide layer can have a general formula of MoO.sub.(2+x).
[0077] In the next step, the fourth top electrode layer is formed
above the molybdenum oxide oxygen-rich metal oxide layer to
complete the formation of the capacitor stack. The fourth top
electrode layer may include one of metals, metal alloys, conductive
metal oxides, conductive metal nitrides, conductive metal
silicides, or combinations thereof, etc. In some embodiments, the
fourth top electrode layer is a noble metal such as platinum or
ruthenium. In some embodiments, the fourth top electrode layer is a
conductive metal nitride. Examples of suitable materials for the
fourth top electrode layer include titanium nitride, titanium
aluminum nitride, titanium silicon nitride, tantalum nitride,
tantalum aluminum nitride, or tantalum silicon nitride. Examples of
suitable conductive metal nitrides include titanium nitride,
titanium aluminum nitride, titanium silicon nitride, tantalum
nitride, tantalum aluminum nitride, or tantalum silicon nitride,
nickel nitride, tungsten nitride, vanadium nitride, molybdenum
nitride, and cobalt nitride, or combinations thereof. The capacitor
stack may receive a PMA treatment as discussed previously. In some
embodiments, the PMA treatment is performed soon (i.e. before
further processing steps) after the forming of the fourth top
electrode layer.
[0078] In some embodiments, the first bottom electrode layer
includes titanium nitride and the second bottom electrode layer
includes molybdenum oxide. Optionally, the first bottom electrode
layer and the second bottom electrode layer are subjected to an
annealing treatment before the deposition of a subsequent
dielectric layer. In some embodiments, the dielectric layer
includes doped titanium oxide. Optionally, the dielectric layer is
subjected to an annealing treatment before the deposition of a
subsequent oxygen-rich metal oxide layer. In some embodiments, the
oxygen-rich metal oxide layer includes molybdenum oxide. In some
embodiments, the fourth top electrode layer includes titanium
nitride. Optionally, the capacitor stack may be subjected to a PMA
treatment. In some embodiments, the PMA treatment is performed soon
(i.e. before further processing steps) after the forming of the
fourth top electrode layer.
[0079] In some embodiments, the first bottom electrode layer
includes titanium aluminum nitride and the second bottom electrode
layer includes molybdenum oxide. Optionally, the first bottom
electrode layer and the second bottom electrode layer are subjected
to an annealing treatment before the deposition of a subsequent
dielectric layer. In some embodiments, the dielectric layer
includes doped titanium oxide. Optionally, the dielectric layer is
subjected to an annealing treatment before the deposition of a
subsequent oxygen-rich metal oxide layer. In some embodiments, the
oxygen-rich metal oxide layer includes molybdenum oxide. In some
embodiments, the fourth top electrode layer includes titanium
aluminum nitride. Optionally, the capacitor stack may be subjected
to a PMA treatment. In some embodiments, the PMA treatment is
performed soon (i.e. before further processing steps) after the
forming of the fourth top electrode layer.
[0080] In some embodiments, the first bottom electrode layer
includes titanium silicon nitride and the second bottom electrode
layer includes molybdenum oxide. Optionally, the first bottom
electrode layer and the second bottom electrode layer are subjected
to an annealing treatment before the deposition of a subsequent
dielectric layer. In some embodiments, the dielectric layer
includes doped titanium oxide. Optionally, the dielectric layer is
subjected to an annealing treatment before the deposition of a
subsequent oxygen-rich metal oxide layer. In some embodiments, the
oxygen-rich metal oxide layer includes molybdenum oxide. In some
embodiments, the fourth top electrode layer includes titanium
silicon nitride. Optionally, the capacitor stack may be subjected
to a PMA treatment. In some embodiments, the PMA treatment is
performed soon (i.e. before further processing steps) after the
forming of the fourth top electrode layer.
[0081] In some embodiments, the first bottom electrode layer
includes tantalum nitride and the second bottom electrode layer
includes molybdenum oxide. Optionally, the first bottom electrode
layer and the second bottom electrode layer are subjected to an
annealing treatment before the deposition of a subsequent
dielectric layer. In some embodiments, the dielectric layer
includes doped titanium oxide. Optionally, the dielectric layer is
subjected to an annealing treatment before the deposition of a
subsequent oxygen-rich metal oxide layer. In some embodiments, the
oxygen-rich metal oxide layer includes molybdenum oxide. In some
embodiments, the fourth top electrode layer includes tantalum
nitride. Optionally, the capacitor stack may be subjected to a PMA
treatment. In some embodiments, the PMA treatment is performed soon
(i.e. before further processing steps) after the forming of the
fourth top electrode layer.
[0082] In some embodiments, the first bottom electrode layer
includes tantalum aluminum nitride and the second bottom electrode
layer includes molybdenum oxide. Optionally, the first bottom
electrode layer and the second bottom electrode layer are subjected
to an annealing treatment before the deposition of a subsequent
dielectric layer. In some embodiments, the dielectric layer
includes doped titanium oxide. Optionally, the dielectric layer is
subjected to an annealing treatment before the deposition of a
subsequent oxygen-rich metal oxide layer. In some embodiments, the
oxygen-rich metal oxide layer includes molybdenum oxide. In some
embodiments, the fourth top electrode layer includes tantalum
aluminum nitride. Optionally, the capacitor stack may be subjected
to a PMA treatment. In some embodiments, the PMA treatment is
performed soon (i.e. before further processing steps) after the
forming of the fourth top electrode layer.
[0083] In some embodiments, the first bottom electrode layer
includes tantalum silicon nitride and the second bottom electrode
layer includes molybdenum oxide. Optionally, the first bottom
electrode layer and the second bottom electrode layer are subjected
to an annealing treatment before the deposition of a subsequent
dielectric layer. In some embodiments, the dielectric layer
includes doped titanium oxide. Optionally, the dielectric layer is
subjected to an annealing treatment before the deposition of a
subsequent oxygen-rich metal oxide layer. In some embodiments, the
oxygen-rich metal oxide layer includes molybdenum oxide. In some
embodiments, the fourth top electrode layer includes tantalum
silicon nitride. Optionally, the capacitor stack may be subjected
to a PMA treatment. In some embodiments, the PMA treatment is
performed soon (i.e. before further processing steps) after the
forming of the fourth top electrode layer.
[0084] FIG. 5 describes a method, 500, for fabricating a DRAM
capacitor stack. The initial step, 502, includes forming a first
bottom electrode layer above a substrate, wherein the first bottom
electrode layer comprises a metal element. Examples of suitable
electrode materials include metals, conductive metal oxides,
conductive metal silicides, conductive metal nitrides, and
combinations thereof. Two particularly interesting classes of
materials are the conductive metal oxides and the conductive metal
nitrides. The purpose of the first bottom electrode layer is to
serve as a primary conductor. Examples of suitable materials for
the first bottom electrode layer include titanium nitride, titanium
aluminum nitride, titanium silicon nitride, tantalum nitride,
tantalum aluminum nitride, or tantalum silicon nitride.
[0085] The next step, 504, includes forming a second bottom
electrode layer above the first bottom electrode layer, wherein the
second bottom electrode layer comprises a metal element. Examples
of suitable electrode materials include metals, conductive metal
oxides, conductive metal silicides, conductive metal nitrides, and
combinations thereof. Two particularly interesting classes of
materials are the conductive metal oxides and the conductive metal
nitrides. The purpose of the second bottom electrode layer is to
promote a desired crystallographic orientation of a subsequently
deposited dielectric layer. As discussed previously, the k-value of
a dielectric material may vary as a function of its
crystallographic orientation. Examples of suitable materials for
the second bottom electrode layer include molybdenum oxide,
chromium oxide, cobalt oxide, iridium oxide, manganese oxide,
nickel oxide, ruthenium oxide, tin oxide, or tungsten oxide. The
first bottom electrode layer and the second bottom electrode layer
can then be subjected to an annealing process (not shown). The
annealing step serves to crystallize the bottom electrode
layers.
[0086] The next step, 506, includes forming a dielectric layer
above the second bottom electrode layer. Optionally, the dielectric
layer can then be subjected to a post dielectric anneal (PDA)
treatment (not shown). The PDA step serves to crystallize the
dielectric material and fill oxygen vacancies.
[0087] The next step, 508, includes forming an oxygen-rich metal
oxide layer above the dielectric layer. The oxygen-rich metal oxide
layer can serve as a source of oxygen to ensure that the
concentration of oxygen vacancies in the dielectric layer does not
increase during subsequent heat treatments.
[0088] The next step, 510, includes forming a third top electrode
layer above the dielectric layer, wherein the third top electrode
layer comprises a metal element. Examples of suitable electrode
materials include metals, conductive metal oxides, conductive metal
silicides, conductive metal nitrides, and combinations thereof. Two
particularly interesting classes of materials are the conductive
metal oxides and the conductive metal nitrides. The purpose of the
third top electrode layer is to promote a desired crystallographic
orientation of a previously deposited dielectric layer. As
discussed previously, the k-value of a dielectric material may vary
as a function of its crystallographic orientation. Examples of
suitable materials for the third top electrode layer include
molybdenum oxide, chromium oxide, cobalt oxide, iridium oxide,
manganese oxide, nickel oxide, ruthenium oxide, tin oxide, or
tungsten oxide.
[0089] The next step, 512, includes forming a fourth top electrode
layer above the third top electrode layer to form a capacitor
stack, wherein the fourth top electrode layer comprises a metal
element. Examples of suitable fourth top electrode materials
include metals, conductive metal oxides, conductive metal
silicides, conductive metal nitrides, and combinations thereof.
Examples of suitable materials for the fourth top electrode layer
include titanium nitride, titanium aluminum nitride, titanium
silicon nitride, tantalum nitride, tantalum aluminum nitride, or
tantalum silicon nitride, or combinations thereof. Optionally, the
capacitor stack can then be subjected to PMA treatment process (not
shown) as discussed previously. In some embodiments, the PMA
treatment is performed soon (i.e. before further processing steps)
after the forming of the fourth top electrode layer.
[0090] FIG. 6 illustrates a simple capacitor stack, 600, consistent
with some embodiments. Using the method as outlined in FIG. 5 and
described above, first bottom electrode layer, 604, is formed above
substrate, 602. Generally, the substrate has already received
several processing steps in the manufacture of a full DRAM device.
First bottom electrode layer, 604, can include one of metals,
conductive metal oxides, conductive metal nitrides, conductive
metal silicides, and combinations thereof. In some embodiments, the
first bottom electrode material is a conductive metal nitride.
Examples of suitable conductive metal nitrides include titanium
nitride, titanium aluminum nitride, titanium silicon nitride,
tantalum nitride, tantalum aluminum nitride, or tantalum silicon
nitride, nickel nitride, tungsten nitride, vanadium nitride,
molybdenum nitride, and cobalt nitride, or combinations
thereof.
[0091] In the next step, a second bottom electrode layer, 606, is
formed above the first bottom electrode layer, wherein the second
bottom electrode layer comprises a metal element. Examples of
suitable electrode materials include metals, conductive metal
oxides, conductive metal silicides, conductive metal nitrides, and
combinations thereof. Two particularly interesting classes of
materials are the conductive metal oxides and the conductive metal
nitrides. Examples of suitable materials for the second bottom
electrode layer include molybdenum oxide, chromium oxide, cobalt
oxide, iridium oxide, manganese oxide, nickel oxide, ruthenium
oxide, tin oxide, or tungsten oxide.
[0092] In the next step, dielectric layer, 608, would then be
formed above the second bottom electrode layer, 606. A wide variety
of dielectric materials have been targeted for use in DRAM
capacitors. Examples of suitable dielectric materials include
aluminum oxide, barium-strontium-titanate (BST), erbium oxide,
hafnium oxide, lanthanum oxide, niobium oxide,
lead-zirconium-titanate (PZT), a bilayer of silicon oxide and
silicon nitride, silicon oxy-nitride, strontium titanate (STO),
tantalum oxide, titanium oxide, zirconium oxide, or doped versions
of the same. These dielectric materials may be formed as a single
layer or may be formed as a hybrid or nanolaminate structure. In
some embodiments, the dielectric material is titanium oxide. In
some embodiments, the dielectric material is doped titanium oxide.
Typical dopants for titanium oxide include Al, Ce, Co, Er, Ga, Gd,
Ge, Hf, In, La, Lu, Mg, Mn, Nd, Pr, Sc, Si, Sn, Sr, Y, Zr, or
combinations thereof.
[0093] In the next step, oxygen-rich metal oxide layer 610, would
then be formed above the dielectric layer, 608.
[0094] In the next step, third top electrode layer 612, would then
be formed above the oxygen-rich metal oxide layer, 610, wherein the
third top electrode layer comprises a metal element. Examples of
suitable electrode materials include metals, conductive metal
oxides, conductive metal silicides, conductive metal nitrides, and
combinations thereof. Two particularly interesting classes of
materials are the conductive metal oxides and the conductive metal
nitrides. Examples of suitable materials for the third top
electrode layer include molybdenum oxide, chromium oxide, cobalt
oxide, iridium oxide, manganese oxide, nickel oxide, ruthenium
oxide, tin oxide, or tungsten oxide.
[0095] In the next step, the fourth top electrode layer, 614, is
formed above third top electrode layer, 612, to form a capacitor
stack. The fourth top electrode layer can include at least one of
metals, conductive metal oxides, conductive metal nitrides,
conductive metal silicides, conductive metal carbides, and
combinations thereof. Examples of suitable materials for the fourth
top electrode layer include titanium nitride, titanium aluminum
nitride, titanium silicon nitride, tantalum nitride, tantalum
aluminum nitride, or tantalum silicon nitride, or combinations
thereof. Typically, the capacitor stack would then be subjected to
a PMA treatment. In some embodiments, the PMA treatment is
performed soon (i.e. before further processing steps) after the
forming of the fourth top electrode layer.
[0096] In some embodiments, a DRAM MIM capacitor stack includes a
first bottom electrode layer including between about 5 nm and about
10 nm of a conductive metal nitride formed on a substrate. Examples
of suitable conductive metal nitrides include titanium nitride,
titanium aluminum nitride, titanium silicon nitride, tantalum
nitride, tantalum aluminum nitride, or tantalum silicon nitride,
nickel nitride, tungsten nitride, vanadium nitride, molybdenum
nitride, and cobalt nitride, or combinations thereof. The
conductive metal nitride first bottom electrode material is formed
at a process temperature between about 150C and 400C using an ALD
or CVD process technology. Optionally, the substrate with the first
bottom electrode layer is then treated as discussed previously.
[0097] In some embodiments, a second bottom electrode layer
including between about 5 nm and about 10 nm of molybdenum oxide is
formed above the first bottom electrode layer. The molybdenum oxide
second bottom electrode layer is formed at a process temperature
between about 150C and 400C using an ALD process technology.
Optionally, the substrate with the first bottom electrode layer and
the second bottom electrode layer is then annealed in an inert
(e.g. argon or nitrogen) or a reducing atmosphere for between about
1 millisecond and about 60 minutes. In some embodiments, the
reducing atmosphere includes between about 1% and about 20% H.sub.2
in N.sub.2 and advantageously between about 5% and about 10%
H.sub.2 in N.sub.2 between 400 and 520C.
[0098] A dielectric layer would then be formed on the annealed
second bottom electrode layer. A wide variety of dielectric
materials have been targeted for use in DRAM capacitors. Examples
of suitable dielectric materials include aluminum oxide,
barium-strontium-titanate (BST), erbium oxide, hafnium oxide,
lanthanum oxide, niobium oxide, lead-zirconium-titanate (PZT), a
bilayer of silicon oxide and silicon nitride, silicon oxy-nitride,
strontium titanate (STO), tantalum oxide, titanium oxide, zirconium
oxide, or doped versions of the same. These dielectric materials
may be formed as a single layer or may be formed as a hybrid or
nanolaminate structure. Typically, the dielectric layer is
subjected to a PDA treatment before the formation of the fourth top
electrode layer as discussed previously. A dielectric material of
interest is titanium oxide doped with aluminum (e.g. as aluminum
oxide) to between about 5 atomic % and about 15 atomic % Al as
calculated by (Al/(Al+Ti)).
[0099] In a specific example, the dielectric layer comprises
between about 6 nm to about 10 nm of TiO.sub.2 wherein at least 30%
of the TiO.sub.2 is present in the rutile phase. Generally, the
TiO.sub.2 dielectric layer may either be a single film or may
comprise a nanolaminate. Advantageously, the TiO.sub.2 material is
doped with Al at a concentration between about 5 atomic % and about
15 atomic % Al as calculated by (Al/(Al+Ti)). The TiO.sub.2
dielectric layer is formed at a process temperature between about
200C and 350C using an ALD process technology. The substrate with
the first electrode and dielectric layer is then annealed in an
oxidizing atmosphere comprising between about 0% O.sub.2 to about
100% O.sub.2 in N.sub.2 and advantageously between about 0% O.sub.2
to about 20% O.sub.2 in N.sub.2 at temperatures between about 400C
to about 600C for between about 1 millisecond to about 60
minutes.
[0100] In the next step, an oxygen-rich metal oxide layer including
between about 0.1 nm and about 5.0 nm of molybdenum oxide is formed
above the dielectric layer. In some embodiments, the oxygen-rich
metal oxide layer includes between about 0.1 nm and 2.0 nm of
molybdenum oxide. The oxygen-rich metal oxide layer (e.g.
molybdenum oxide) is formed at a process temperature between about
150C and 400C using an ALD process technology. The molybdenum oxide
oxygen-rich metal oxide layer can have a general formula of
Mo.sub.(2+x).
[0101] In some embodiments, a third top electrode layer including
between about 2 nm and about 10 nm of molybdenum oxide is formed
above the oxygen-rich metal oxide layer. The molybdenum oxide third
top electrode layer is formed at a process temperature between
about 150C and 400C using an ALD process technology.
[0102] In the next step, the fourth top electrode layer is formed
above the third top electrode layer to complete the formation of
the capacitor stack. The fourth top electrode layer may include one
of metals, metal alloys, conductive metal oxides, conductive metal
nitrides, conductive metal silicides, or combinations thereof, etc.
In some embodiments, the fourth top electrode layer is a noble
metal such as platinum or ruthenium. In some embodiments, the
fourth top electrode layer is a conductive metal nitride. Examples
of suitable conductive metal nitrides include titanium nitride,
titanium aluminum nitride, titanium silicon nitride, tantalum
nitride, tantalum aluminum nitride, or tantalum silicon nitride,
nickel nitride, tungsten nitride, vanadium nitride, molybdenum
nitride, and cobalt nitride, or combinations thereof. The capacitor
stack may receive a PMA treatment as discussed previously. In some
embodiments, the PMA treatment is performed soon (i.e. before
further processing steps) after the forming of the fourth top
electrode layer.
[0103] In some embodiments, the first bottom electrode layer
includes titanium nitride and the second bottom electrode layer
includes molybdenum oxide. Optionally, the first bottom electrode
layer and the second bottom electrode layer are subjected to an
annealing treatment before the deposition of a subsequent
dielectric layer. In some embodiments, the dielectric layer
includes doped titanium oxide. Optionally, the dielectric layer is
subjected to an annealing treatment before the deposition of a
subsequent oxygen-rich metal oxide layer. In some embodiments, the
oxygen-rich metal oxide layer includes molybdenum oxide. In some
embodiments, the third top electrode layer includes molybdenum
oxide. In some embodiments, the fourth top electrode layer includes
titanium nitride. Optionally, the capacitor stack may be subjected
to a PMA treatment. In some embodiments, the PMA treatment is
performed soon (i.e. before further processing steps) after the
forming of the fourth top electrode layer.
[0104] In some embodiments, the first bottom electrode layer
includes titanium aluminum nitride and the second bottom electrode
layer includes molybdenum oxide. Optionally, the first bottom
electrode layer and the second bottom electrode layer are subjected
to an annealing treatment before the deposition of a subsequent
dielectric layer. In some embodiments, the dielectric layer
includes doped titanium oxide. Optionally, the dielectric layer is
subjected to an annealing treatment before the deposition of a
subsequent oxygen-rich metal oxide layer. In some embodiments, the
oxygen-rich metal oxide layer includes molybdenum oxide. In some
embodiments, the third top electrode layer includes molybdenum
oxide. In some embodiments, the fourth top electrode layer includes
titanium aluminum nitride. Optionally, the capacitor stack may be
subjected to a PMA treatment. In some embodiments, the PMA
treatment is performed soon (i.e. before further processing steps)
after the forming of the fourth top electrode layer.
[0105] In some embodiments, the first bottom electrode layer
includes titanium silicon nitride and the second bottom electrode
layer includes molybdenum oxide. Optionally, the first bottom
electrode layer and the second bottom electrode layer are subjected
to an annealing treatment before the deposition of a subsequent
dielectric layer. In some embodiments, the dielectric layer
includes doped titanium oxide. Optionally, the dielectric layer is
subjected to an annealing treatment before the deposition of a
subsequent oxygen-rich metal oxide layer. In some embodiments, the
oxygen-rich metal oxide layer includes molybdenum oxide. In some
embodiments, the third top electrode layer includes molybdenum
oxide. In some embodiments, the fourth top electrode layer includes
titanium silicon nitride. Optionally, the capacitor stack may be
subjected to a PMA treatment. In some embodiments, the PMA
treatment is performed soon (i.e. before further processing steps)
after the forming of the fourth top electrode layer.
[0106] In some embodiments, the first bottom electrode layer
includes tantalum nitride and the second bottom electrode layer
includes molybdenum oxide. Optionally, the first bottom electrode
layer and the second bottom electrode layer are subjected to an
annealing treatment before the deposition of a subsequent
dielectric layer. In some embodiments, the dielectric layer
includes doped titanium oxide. Optionally, the dielectric layer is
subjected to an annealing treatment before the deposition of a
subsequent oxygen-rich metal oxide layer. In some embodiments, the
oxygen-rich metal oxide layer includes molybdenum oxide. In some
embodiments, the third top electrode layer includes molybdenum
oxide. In some embodiments, the fourth top electrode layer includes
tantalum nitride. Optionally, the capacitor stack may be subjected
to a PMA treatment. In some embodiments, the PMA treatment is
performed soon (i.e. before further processing steps) after the
forming of the fourth top electrode layer.
[0107] In some embodiments, the first bottom electrode layer
includes tantalum aluminum nitride and the second bottom electrode
layer includes molybdenum oxide. Optionally, the first bottom
electrode layer and the second bottom electrode layer are subjected
to an annealing treatment before the deposition of a subsequent
dielectric layer. In some embodiments, the dielectric layer
includes doped titanium oxide. Optionally, the dielectric layer is
subjected to an annealing treatment before the deposition of a
subsequent oxygen-rich metal oxide layer. In some embodiments, the
oxygen-rich metal oxide layer includes molybdenum oxide. In some
embodiments, the third top electrode layer includes molybdenum
oxide. In some embodiments, the fourth top electrode layer includes
tantalum aluminum nitride. Optionally, the capacitor stack may be
subjected to a PMA treatment. In some embodiments, the PMA
treatment is performed soon (i.e. before further processing steps)
after the forming of the fourth top electrode layer.
[0108] In some embodiments, the first bottom electrode layer
includes tantalum silicon nitride and the second bottom electrode
layer includes molybdenum oxide. Optionally, the first bottom
electrode layer and the second bottom electrode layer are subjected
to an annealing treatment before the deposition of a subsequent
dielectric layer. In some embodiments, the dielectric layer
includes doped titanium oxide. Optionally, the dielectric layer is
subjected to an annealing treatment before the deposition of a
subsequent oxygen-rich metal oxide layer. In some embodiments, the
oxygen-rich metal oxide layer includes molybdenum oxide. In some
embodiments, the third top electrode layer includes molybdenum
oxide. In some embodiments, the fourth top electrode layer includes
tantalum silicon nitride. Optionally, the capacitor stack may be
subjected to a PMA treatment. In some embodiments, the PMA
treatment is performed soon (i.e. before further processing steps)
after the forming of the fourth top electrode layer.
[0109] Titanium nitride has been widely used as both the first
bottom electrode layer and the fourth top electrode layer in DRAM
devices. However, titanium nitride is sensitive to oxidation. The
surface of the titanium nitride layer will react with oxidants to
form a titanium oxy-nitride layer. This titanium oxy-nitride layer
has high resistivity and poor materials properties, leading to
increased leakage current through the device. The titanium nitride
can be subject to oxidation when exposed to aggressive oxidants
such as ozone during subsequent layer depositions using ALD
techniques.
[0110] Tantalum nitride is a metal nitride candidate to replace
titanium nitride in the electrode structures of DRAM devices.
Tantalum nitride has a higher resistance to oxidation than titanium
nitride. FIG. 7 presents data for the % increase in sheet
resistance for several materials according to some embodiments.
Sheet resistance is an indicator of oxidation because oxynitrides
have higher sheet resistance than the corresponding nitrides. A
titanium nitride control group of samples was prepared using
reactive sputtering in 100% nitrogen in argon (represented by
square data points). The titanium nitride samples each had a
thickness of about 20 nm. Two groups of tantalum nitride samples
were prepared using reactive sputtering using nitrogen in argon. A
first group of tantalum nitride samples were prepared using 12.5%
nitrogen in argon (represented by diamond data points). A second
group of tantalum nitride samples were prepared using 20.0%
nitrogen in argon (represented by triangular data points). The
tantalum nitride samples each had a thickness of about 20 nm.
[0111] Samples from each group were subjected to a rapid thermal
process (RTP) treatment using 4% oxygen in nitrogen at temperatures
between 360C and 500C. Each RTP treatment was made for 10 minutes.
The sheet resistance (Rs) was measured for each sample before and
after the RTP treatment. FIG. 7 presents data for the %-increase in
the Rs for each of the sample groups as a function of RTP treatment
temperature. The sheet resistance of the titanium nitride control
samples (represented by square data points) increased by more than
5000% at an RTP treatment temperature of 500C. In contrast, the
sheet resistance of both of the tantalum nitride sample groups
(represented by diamond data points and triangular data points)
increased by less than 40% at an RTP treatment temperature of 500C.
From this data, it can be concluded that tantalum nitride has a
stronger resistance to oxidation than titanium nitride.
[0112] One of the benefits of titanium nitride is its ability to
promote the MoO.sub.2 compound of molybdenum oxide. As discussed
previously, MoO.sub.2 has a distorted rutile crystal structure and
serves as a good template of the high-k rutile phase of titanium
oxide. If tantalum nitride is to replace titanium nitride in the
electrode structures of DRAM capacitors, it must also promote the
MoO.sub.2 compound of molybdenum oxide.
[0113] FIG. 8 presents x-ray diffraction (XRD) data for MoO.sub.x
materials according to some embodiments. The spectra present XRD
data for 20 nm of molybdenum oxide deposited on 60 nm of tantalum
nitride. The tantalum nitride layer was deposited by reactive
sputtering using 15.0% nitrogen in argon. The molybdenum oxide was
deposited by ALD. The spectrum, 802, presents XRD data for the film
stack "as deposited". That is, no subsequent annealing treatments
have been performed. The peaks at .about.42 degrees 2-theta and
.about.36 degrees 2-theta correspond to the tantalum nitride layer.
There are no peaks at .about.26 degrees 2-theta and .about.54
degrees 2-theta, indicating that the molybdenum oxide is amorphous
in the as-deposited state. The spectrum, 804, presents XRD data for
the film stack after annealing the stack for 10 minutes at 400C in
nitrogen. There are peaks at .about.26 degrees 2-theta and
.about.54 degrees 2-theta, indicating that the molybdenum oxide has
begun to crystallize to the MoO.sub.2 phase after this annealing
treatment. The spectrum, 806, presents XRD data for the film stack
after annealing the stack for 10 minutes at 450C in nitrogen. There
are peaks at .about.26 degrees 2-theta and .about.54 degrees
2-theta, indicating that the molybdenum oxide has begun to
crystallize to the MoO.sub.2 phase after this annealing treatment.
The MoO.sub.2 peaks are more intense and sharper (e.g. narrower)
than the peaks in spectrum 804. This indicates that the molybdenum
oxide layer annealed at 450C has higher crystallinity than the
sample annealed at 400C. The spectrum, 808, presents XRD data for
the film stack after annealing the stack for 10 minutes at 500C in
nitrogen. There are peaks at .about.26 degrees 2-theta and
.about.54 degrees 2-theta, indicating that the molybdenum oxide has
begun to crystallize to the MoO.sub.2 phase after this annealing
treatment. The MoO.sub.2 peaks are more intense and sharper (e.g.
narrower) than the peaks in spectrum 804 or 806. This indicates
that the molybdenum oxide layer annealed at 500C has higher
crystallinity than the samples annealed at 400C or 450C.
[0114] Capacitor stacks were formed to evaluate the electrical
performance using tantalum nitride as the first bottom electrode
layer. A first bottom electrode layer including 60 nm of tantalum
nitride was formed using reactive sputtering in 15% nitrogen. A
second bottom electrode layer including 5 nm of molybdenum oxide
was formed using ALD on top of the tantalum nitride. The tantalum
nitride and the molybdenum oxide were subjected to an anneal at
500C for 10 minutes in nitrogen to crystallize the molybdenum
oxide.
[0115] A dielectric layer including 5.2 nm of titanium oxide doped
with 15% of Al, calculated as (Al/(Al+Ti)), was formed using ALD on
top of the molybdenum oxide. A dielectric layer including 1.2 nm of
zirconium oxide was formed using ALD on top of the titanium oxide.
The doped titanium oxide layer and the zirconium oxide layer form a
dielectric nanolaminate. This nanolaminate will be designated as
"TAZ" in the discussion below. The dielectric nanolaminate was
subjected to an anneal at 400C for 10 minutes in dilute oxygen
(e.g. less than 10% oxygen).
[0116] A top electrode including platinum was deposited using PVD
through a shadow mask to form stacked capacitor structures.
Current-Voltage (IN), Capacitance-Voltage (CN), and leakage current
density (J in units of A/cm.sup.2) data were collected in the
voltage range between -5V and +5V. Table 1 presents data for two
groups of samples using tantalum nitride compared to a control
group of samples using titanium nitride. Each sample group
represents the average of 18 devices. The data in Table 1 indicate
that the use of tantalum nitride in the electrode structures for
DRAM capacitors has no negative effects.
TABLE-US-00001 TABLE 1 Dielec- Dielec- Bottom tric tric Top J at 1
V EOT Electrode Material Thickness Electrode (A/cm.sup.2) (nm)
K-value TaN/MoO.sub.2 TAZ 6.4 Pt 1.3E-7 0.53 47.4 TaN/MoO.sub.2 TAZ
6.4 Pt 1.7E-7 0.52 48.0 TiN/MoO.sub.2 TAZ 6.4 Pt 1.7E-7 0.52
48.0
[0117] An example of a specific application of some embodiments is
in the fabrication of capacitors used in the memory cells in DRAM
devices. DRAM memory cells effectively use a capacitor to store
charge for a period of time, with the charge being electronically
"read" to determine whether a logical "one" or "zero" has been
stored in the associated cell. Conventionally, a cell transistor is
used to access the cell. The cell transistor is turned "on" in
order to store data on each associated capacitor and is otherwise
turned "off" to isolate the capacitor and preserve its charge. More
complex DRAM cell structures exist, but this basic DRAM structure
will be used for illustrating the application of this disclosure to
capacitor manufacturing and to DRAM manufacturing. FIG. 9 is used
to illustrate one DRAM cell, 920, manufactured using a dielectric
structure as discussed previously. The cell, 920, is illustrated
schematically to include two principal components, a cell
capacitor, 900, and a cell transistor, 902. The cell transistor is
usually constituted by a MOS transistor having a gate, 918, source,
914, and drain, 916. The gate is usually connected to a word line
and one of the source or drain is connected to a bit line. The cell
capacitor has a lower or storage electrode, 906+908, and an upper
or plate electrode, 912. The storage electrode is connected to the
other of the source or drain and the plate electrode is connected
to a reference potential conductor (not shown). The cell transistor
is, when selected, turned "on" by an active level of the word line
to read or write data from or into the cell capacitor via the bit
line.
[0118] As was described previously, the cell capacitor, 900,
includes a first bottom electrode layer, 906, formed above
substrate, 904. The first bottom electrode layer, 906, is connected
to the source or drain of the cell transistor, 902. For
illustrative purposes, the first bottom electrode has been
connected to the source, 914, in this example. First bottom
electrode layer, 906, can include one of metals, conductive metal
oxides, conductive metal nitrides, conductive metal silicides, and
combinations thereof. In some embodiments, the first bottom
electrode material is a conductive metal nitride. Examples of
suitable conductive metal nitrides include titanium nitride,
titanium aluminum nitride, titanium silicon nitride, tantalum
nitride, tantalum aluminum nitride, or tantalum silicon nitride,
nickel nitride, tungsten nitride, vanadium nitride, molybdenum
nitride, and cobalt nitride, or combinations thereof. In some
embodiments, the first bottom electrode material is tantalum
nitride.
[0119] A second bottom electrode layer, 908, is formed above the
first bottom electrode layer. Examples of suitable second bottom
electrode materials include metals, conductive metal oxides,
conductive metal silicides, conductive metal nitrides, and
combinations thereof. Two particularly interesting classes of 2
materials are the conductive metal oxides and the conductive metal
nitrides. Examples of suitable materials for the second bottom
electrode layer include molybdenum oxide, chromium oxide, cobalt
oxide, iridium oxide, manganese oxide, nickel oxide, ruthenium
oxide, tin oxide, or tungsten oxide. In some embodiments, second
bottom electrode layer includes molybdenum oxide. As discussed
previously, first bottom electrode layer, 906, and second bottom
electrode layer, 908, may be subjected to an anneal before the
formation of the dielectric layer if the second bottom electrode
layer is a conductive metal oxide (e.g. molybdenum oxide).
[0120] Crystalline, doped, high-k dielectric layer, 910, is formed
above the second bottom electrode layer. Examples of suitable
dielectric materials include aluminum oxide,
barium-strontium-titanate (BST), erbium oxide, hafnium oxide,
lanthanum oxide, niobium oxide, lead-zirconium-titanate (PZT), a
bilayer of silicon oxide and silicon nitride, silicon oxy-nitride,
strontium titanate (STO), tantalum oxide, titanium oxide, zirconium
oxide, or doped versions of the same. These dielectric materials
may be formed as a single layer or may be formed as a hybrid or
nanolaminate structure. In some embodiments, the dielectric
material is titanium oxide. In some embodiments, the dielectric
material is doped titanium oxide. Typical dopants for titanium
oxide include Al, Ce, Co, Er, Ga, Gd, Ge, Hf, In, La, Lu, Mg, Mn,
Nd, Pr, Sc, Si, Sn, Sr, Y, Zr, or combinations thereof. Typically,
the first bottom electrode layer, the second bottom electrode
layer, and the high-k dielectric layer are then subjected to a PDA
treatment. The fourth top electrode layer, 912, is then formed
above the dielectric layer. The fourth top electrode layer can
include at least one of metals, conductive metal oxides, conductive
metal nitrides, conductive metal silicides, conductive metal
carbides, and combinations thereof. Examples of suitable conductive
metal nitrides include titanium nitride, titanium aluminum nitride,
titanium silicon nitride, tantalum nitride, tantalum aluminum
nitride, or tantalum silicon nitride, nickel nitride, tungsten
nitride, vanadium nitride, molybdenum nitride, and cobalt nitride,
or combinations thereof. This completes the formation of the
capacitor stack. Typically, the capacitor stack is then subjected
to a PMA treatment. In some embodiments, the PMA treatment is
performed soon (i.e. before further processing steps) after the
forming of the fourth top electrode layer.
[0121] In some embodiments, first bottom electrode layer, 906,
includes tantalum nitride, second bottom electrode layer, 908,
includes molybdenum oxide, dielectric layer, 910, includes a
nanolaminate of aluminum-doped titanium oxide and zirconium oxide,
and fourth top electrode layer, 912, includes titanium nitride.
[0122] An example of a specific application of some embodiments is
in the fabrication of capacitors used in the memory cells in DRAM
devices. DRAM memory cells effectively use a capacitor to store
charge for a period of time, with the charge being electronically
"read" to determine whether a logical "one" or "zero" has been
stored in the associated cell. Conventionally, a cell transistor is
used to access the cell. The cell transistor is turned "on" in
order to store data on each associated capacitor and is otherwise
turned "off" to isolate the capacitor and preserve its charge. More
complex DRAM cell structures exist, but this basic DRAM structure
will be used for illustrating the application of this disclosure to
capacitor manufacturing and to DRAM manufacturing. FIG. 10 is used
to illustrate one DRAM cell, 1022, manufactured using a dielectric
structure as discussed previously. The cell, 1022, is illustrated
schematically to include two principal components, a cell
capacitor, 1000, and a cell transistor, 1002. The cell transistor
is usually constituted by a MOS transistor having a gate, 1020,
source, 1016, and drain, 1018. The gate is usually connected to a
word line and one of the source or drain is connected to a bit
line. The cell capacitor has a lower or storage electrode,
1006+1008, and an upper or plate electrode, 1014. The storage
electrode is connected to the other of the source or drain and the
plate electrode is connected to a reference potential conductor.
The cell transistor is, when selected, turned "on" by an active
level of the word line to read or write data from or into the cell
capacitor via the bit line.
[0123] As was described previously, the cell capacitor, 1000,
includes a first bottom electrode layer, 1006, formed above
substrate, 1004. The first bottom electrode layer, 1006, is
connected to the source or drain of the cell transistor, 1002. For
illustrative purposes, the first bottom electrode has been
connected to the source, 1016, in this example. First bottom
electrode layer, 1006, can include one of metals, conductive metal
oxides, conductive metal nitrides, conductive metal silicides, and
combinations thereof. In some embodiments, the first bottom
electrode material is a conductive metal nitride. Examples of
suitable conductive metal nitrides include titanium nitride,
titanium aluminum nitride, titanium silicon nitride, tantalum
nitride, tantalum aluminum nitride, or tantalum silicon nitride,
nickel nitride, tungsten nitride, vanadium nitride, molybdenum
nitride, and cobalt nitride, or combinations thereof. In some
embodiments, the first bottom electrode material is tantalum
nitride.
[0124] A second bottom electrode layer, 1008, is formed above the
first bottom electrode layer. Examples of suitable second bottom
electrode materials include metals, conductive metal oxides,
conductive metal silicides, conductive metal nitrides, and
combinations thereof. Two particularly interesting classes of
materials are the conductive metal oxides and the conductive metal
nitrides. Examples of suitable materials for the second bottom
electrode layer include molybdenum oxide, chromium oxide, cobalt
oxide, iridium oxide, manganese oxide, nickel oxide, ruthenium
oxide, tin oxide, or tungsten oxide. In some embodiments, second
bottom electrode layer includes molybdenum oxide. As discussed
previously, first bottom electrode layer, 1006, and second bottom
electrode layer, 1008, may be subjected to an anneal before the
formation of the dielectric layer if the second bottom electrode
layer is a conductive metal oxide (e.g. molybdenum oxide).
[0125] Crystalline, doped, high-k dielectric layer, 1010, is formed
above the second bottom electrode layer. Examples of suitable
dielectric materials include aluminum oxide,
barium-strontium-titanate (BST), erbium oxide, hafnium oxide,
lanthanum oxide, niobium oxide, lead-zirconium-titanate (PZT), a
bilayer of silicon oxide and silicon nitride, silicon oxy-nitride,
strontium titanate (STO), tantalum oxide, titanium oxide, zirconium
oxide, or doped versions of the same. These dielectric materials
may be formed as a single layer or may be formed as a hybrid or
nanolaminate structure. In some embodiments, the dielectric
material is titanium oxide. In some embodiments, the dielectric
material is doped titanium oxide. Typical dopants for titanium
oxide include Al, Ce, Co, Er, Ga, Gd, Ge, Hf, In, La, Lu, Mg, Mn,
Nd, Pr, Sc, Si, Sn, Sr, Y, Zr, or combinations thereof. Typically,
the first bottom electrode layer, the second bottom electrode
layer, and the high-k dielectric layer are then subjected to a PDA
treatment.
[0126] Oxygen-rich metal oxide layer, 1012, is then formed above
the dielectric layer, 1010. The oxygen-rich metal oxide layer can
serve as a source of oxygen to ensure that the concentration of
oxygen vacancies in the dielectric layer does not increase during
subsequent heat treatments.
[0127] The fourth top electrode layer, 1014, is then formed above
the oxygen-rich metal oxide layer, 1012. The fourth top electrode
layer can include at least one of metals, conductive metal oxides,
conductive metal nitrides, conductive metal silicides, conductive
metal carbides, and combinations thereof. Examples of suitable
conductive metal nitrides include titanium nitride, titanium
aluminum nitride, titanium silicon nitride, tantalum nitride,
tantalum aluminum nitride, or tantalum silicon nitride, nickel
nitride, tungsten nitride, vanadium nitride, molybdenum nitride,
and cobalt nitride, or combinations thereof. This completes the
formation of the capacitor stack. Typically, the capacitor stack is
then subjected to a PMA treatment. In some embodiments, the PMA
treatment is performed soon (i.e. before further processing steps)
after the forming of the fourth top electrode layer.
[0128] In some embodiments, first bottom electrode layer, 1006,
includes tantalum nitride, second bottom electrode layer, 1008,
includes molybdenum oxide, dielectric layer, 1010, includes a
nanolaminate of aluminum-doped titanium oxide and zirconium oxide,
oxygen-rich metal oxide layer, 1012, includes oxygen-rich
molybdenum oxide, and fourth top electrode layer, 1014, includes
titanium nitride.
[0129] An example of a specific application of some embodiments is
in the fabrication of capacitors used in the memory cells in DRAM
devices. DRAM memory cells effectively use a capacitor to store
charge for a period of time, with the charge being electronically
"read" to determine whether a logical "one" or "zero" has been
stored in the associated cell. Conventionally, a cell transistor is
used to access the cell. The cell transistor is turned "on" in
order to store data on each associated capacitor and is otherwise
turned "off" to isolate the capacitor and preserve its charge. More
complex DRAM cell structures exist, but this basic DRAM structure
will be used for illustrating the application of this disclosure to
capacitor manufacturing and to DRAM manufacturing. FIG. 11 is used
to illustrate one DRAM cell, 1124, manufactured using a dielectric
structure as discussed previously. The cell, 1124, is illustrated
schematically to include two principal components, a cell
capacitor, 1100, and a cell transistor, 1102. The cell transistor
is usually constituted by a MOS transistor having a gate, 1122,
source, 1118, and drain, 1120. The gate is usually connected to a
word line and one of the source or drain is connected to a bit
line. The cell capacitor has a lower or storage electrode,
1106+1108, and an upper or plate electrode, 1116. The storage
electrode is connected to the other of the source or drain and the
plate electrode is connected to a reference potential conductor.
The cell transistor is, when selected, turned "on" by an active
level of the word line to read or write data from or into the cell
capacitor via the bit line.
[0130] As was described previously, the cell capacitor, 1100,
includes a first bottom electrode layer, 1106, formed above
substrate, 1104. The first bottom electrode layer, 1106, is
connected to the source or drain of the cell transistor, 1102. For
illustrative purposes, the first bottom electrode has been
connected to the source, 1118, in this example. First bottom
electrode layer, 1106, can include one of metals, conductive metal
oxides, conductive metal nitrides, conductive metal silicides, and
combinations thereof. In some embodiments, the first bottom
electrode material is a conductive metal nitride. Examples of
suitable conductive metal nitrides include titanium nitride,
titanium aluminum nitride, titanium silicon nitride, tantalum
nitride, tantalum aluminum nitride, or tantalum silicon nitride,
nickel nitride, tungsten nitride, vanadium nitride, molybdenum
nitride, and cobalt nitride, or combinations thereof. In some
embodiments, the first bottom electrode material is tantalum
nitride.
[0131] A second bottom electrode layer, 1108, is formed above the
first bottom electrode layer. Examples of suitable second bottom
electrode materials include metals, conductive metal oxides,
conductive metal silicides, conductive metal nitrides, and
combinations thereof. Two particularly interesting classes of
materials are the conductive metal oxides and the conductive metal
nitrides. Examples of suitable materials for the second bottom
electrode layer include molybdenum oxide, chromium oxide, cobalt
oxide, iridium oxide, manganese oxide, nickel oxide, ruthenium
oxide, tin oxide, or tungsten oxide. In some embodiments, second
bottom electrode layer includes molybdenum oxide. As discussed
previously, first bottom electrode layer, 1106, and second bottom
electrode layer, 1108, may be subjected to an anneal before the
formation of the dielectric layer if the second bottom electrode
layer is a conductive metal oxide (e.g. molybdenum oxide).
[0132] Crystalline, doped, high-k dielectric layer, 1110, is formed
above the second bottom electrode layer. Examples of suitable
dielectric materials include aluminum oxide,
barium-strontium-titanate (BST), erbium oxide, hafnium oxide,
lanthanum oxide, niobium oxide, lead-zirconium-titanate (PZT), a
bilayer of silicon oxide and silicon nitride, silicon oxy-nitride,
strontium titanate (STO), tantalum oxide, titanium oxide, zirconium
oxide, or doped versions of the same. These dielectric materials
may be formed as a single layer or may be formed as a hybrid or
nanolaminate structure. In some embodiments, the dielectric
material is titanium oxide. In some embodiments, the dielectric
material is doped titanium oxide. Typical dopants for titanium
oxide include Al, Ce, Co, Er, Ga, Gd, Ge, Hf, In, La, Lu, Mg, Mn,
Nd, Pr, Sc, Si, Sn, Sr, Y, Zr, or combinations thereof. Typically,
the first bottom electrode layer, the second bottom electrode
layer, and the high-k dielectric layer are then subjected to a PDA
treatment.
[0133] Oxygen-rich metal oxide layer, 1112, is then formed above
the dielectric layer, 1110. The oxygen-rich metal oxide layer can
serve as a source of oxygen to ensure that the concentration of
oxygen vacancies in the dielectric layer does not increase during
subsequent heat treatments.
[0134] In the next step, third top electrode layer 1114, would then
be formed above the oxygen-rich metal oxide layer, 1112, wherein
the third top electrode layer comprises a metal element. Examples
of suitable electrode materials include metals, conductive metal
oxides, conductive metal silicides, conductive metal nitrides, and
combinations thereof. Two particularly interesting classes of
materials are the conductive metal oxides and the conductive metal
nitrides. Examples of suitable materials for the third top
electrode layer include molybdenum oxide, chromium oxide, cobalt
oxide, iridium oxide, manganese oxide, nickel oxide, ruthenium
oxide, tin oxide, or tungsten oxide.
[0135] The fourth top electrode layer, 1116, is then formed above
the third top electrode layer, 1114. The fourth top electrode layer
can include at least one of metals, conductive metal oxides,
conductive metal nitrides, conductive metal silicides, conductive
metal carbides, and combinations thereof. Examples of suitable
conductive metal nitrides include titanium nitride, titanium
aluminum nitride, titanium silicon nitride, tantalum nitride,
tantalum aluminum nitride, or tantalum silicon nitride, nickel
nitride, tungsten nitride, vanadium nitride, molybdenum nitride,
and cobalt nitride, or combinations thereof. This completes the
formation of the capacitor stack. Typically, the capacitor stack is
then subjected to a PMA treatment. In some embodiments, the PMA
treatment is performed soon (i.e. before further processing steps)
after the forming of the fourth top electrode layer.
[0136] In some embodiments, first bottom electrode layer, 1106,
includes tantalum nitride, second bottom electrode layer, 1108,
includes molybdenum oxide, dielectric layer, 1110, includes a
nanolaminate of aluminum-doped titanium oxide and zirconium oxide,
oxygen-rich metal oxide layer, 1112, includes oxygen-rich
molybdenum oxide, third top electrode layer, 1114, includes
molybdenum oxide, and fourth top electrode layer, 1116, includes
titanium nitride.
[0137] Although the foregoing examples have been described in some
detail for purposes of clarity of understanding, the invention is
not limited to the details provided. There are many alternative
ways of implementing the invention. The disclosed examples are
illustrative and not restrictive.
* * * * *