U.S. patent application number 14/507418 was filed with the patent office on 2016-04-07 for doped electrode for dram capacitor stack.
The applicant listed for this patent is Intermolecular, Inc.. Invention is credited to Prashant B. Phatak.
Application Number | 20160099303 14/507418 |
Document ID | / |
Family ID | 55633377 |
Filed Date | 2016-04-07 |
United States Patent
Application |
20160099303 |
Kind Code |
A1 |
Phatak; Prashant B. |
April 7, 2016 |
Doped Electrode for DRAM Capacitor Stack
Abstract
In some embodiments, a metal oxide second electrode material is
formed as part of a MIM DRAM capacitor stack. The second electrode
material is doped with one or more dopants. The dopants may
influence the crystallinity, resistivity, and/or work function of
the second electrode material. The dopants may be uniformly
distributed throughout the second electrode material or may be
distributed with a gradient in their concentration profile.
Inventors: |
Phatak; Prashant B.; (San
Jose, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Intermolecular, Inc. |
San Jose |
CA |
US |
|
|
Family ID: |
55633377 |
Appl. No.: |
14/507418 |
Filed: |
October 6, 2014 |
Current U.S.
Class: |
257/532 |
Current CPC
Class: |
H01L 27/108 20130101;
H01L 21/02197 20130101; H01L 27/10805 20130101; H01L 28/65
20130101; H01L 28/75 20130101; H01L 21/2855 20130101 |
International
Class: |
H01L 49/02 20060101
H01L049/02; H01L 27/108 20060101 H01L027/108 |
Claims
1. A capacitor stack comprising: a first electrode layer formed
above a substrate; a dielectric material formed above the first
electrode layer; and a second electrode structure formed above the
dielectric material; wherein the second electrode structure
comprises a first material layer and a second material layer having
a different composition than the first material layer, wherein the
first material layer directly interfaces the dielectric material
and comprises molybdenum oxide, wherein the first material layer
further comprises a dopant having a concentration of between 1
atomic % and 20 atomic %, wherein the dopant comprises titanium
oxide, and wherein the second material layer comprising titanium
nitride.
2. The capacitor stack of claim 1 wherein the first electrode layer
comprises one of metals, conductive metal oxides, conductive metal
nitrides, or conductive metal silicides.
3. The capacitor stack of claim 2 wherein the first electrode
structure comprises a conductive compound of molybdenum oxide.
4. (canceled)
5. The capacitor stack of claim 1 wherein the dielectric material
comprises one of titanium oxide or zirconium oxide.
6. The capacitor stack of claim 1 wherein the first material layer
of the second electrode structure comprises one of metals,
conductive metal oxides, conductive metal nitrides, or conductive
metal silicides.
7-20. (canceled)
21. The capacitor stack of claim 1 wherein the dopant has a
concentration gradient at least within the first material layer of
the second electrode structure.
22. The capacitor stack of claim 21 wherein the concentration of
the dopant is lowest at an interface with the dielectric
material.
23. The capacitor stack of claim 1 wherein the concentration of the
dopant in the first material layer of the second electrode
structure is between 5 atomic % and 15 atomic %.
24. The capacitor stack of claim 1 wherein the first material layer
of the second electrode structure comprises one of conductive metal
oxides.
25. The capacitor stack of claim 1 wherein the first material layer
of the second electrode structure comprises a conductive compound
of molybdenum oxide.
26. The capacitor stack of claim 1 wherein the first material layer
of the second electrode structure has a rutile crystal
structure.
27. The capacitor stack of claim 1 wherein the dielectric material
comprises one of 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, or zirconium oxide.
28. The capacitor stack of claim 27 wherein the dielectric material
further comprises a dopant.
29. The capacitor stack of claim 1 wherein the dielectric material
has a hybrid structure or a nanolaminate structure.
30. The capacitor stack of claim 1 wherein the dielectric material
is zirconium oxide.
31. The capacitor stack of claim 30 wherein zirconium oxide of the
dielectric material has a tetragonal phase.
32. The capacitor stack of claim 1 wherein the dielectric material
is titanium oxide.
33. The capacitor stack of claim 32 wherein titanium oxide of the
dielectric material has a rutile phase.
34. The capacitor stack of claim 1 wherein the dopant is uniformly
distributed within the first material layer of the second electrode
structure.
Description
FIELD OF THE DISCLOSURE
[0001] The present invention 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 OF THE DISCLOSURE
[0002] 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.o represents the vacuum permittivity.
[0003] 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 (generally <10.sup.-7 A cm.sup.-2). The physical
thickness of the dielectric layers in DRAM capacitors cannot be
reduced without limit in order to avoid leakage current caused by
tunneling mechanisms which exponentially increases as the thickness
of the dielectric layer decreases.
[0004] 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.
[0005] 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.
[0006] 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:
EOT = 3.9 .kappa. d ( Eqn . 2 ) ##EQU00002##
where d represents the physical thickness of the capacitor
dielectric.
[0007] 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.
[0008] One class of high-k dielectric materials possessing the
characteristics required for implementation in advanced DRAM
capacitors are 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.
[0009] 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.
[0010] 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.
[0011] 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, poor adhesion,
and form a contamination risk in the fab.
[0012] 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 600 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.
[0013] 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.
[0014] 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.
[0015] 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. patent
application Ser. No. 13/084,666 (now U.S. Pat. No. 8,813,325) filed
on Apr. 12, 2011 which is herein incorporated by reference for all
purposes. However, it has been difficult to integrate the use of
crystalline MoO.sub.2 as the second (e.g. top) electrode in a DRAM
MIM stack without affecting the underlying dielectric layer.
SUMMARY OF THE DISCLOSURE
[0016] The following summary 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 in a
simplified form as a prelude to the more detailed description that
is presented below.
[0017] In some embodiments, a metal oxide second electrode material
is formed as part of a MIM DRAM capacitor stack. The second
electrode material is doped with one or more dopants. The dopants
may influence the crystallinity, resistivity, and/or work function
of the second electrode material. The dopants may be uniformly
distributed throughout the second electrode material or may be
distributed with a gradient in their concentration profile. The
second electrode material may be formed as a single layer or may be
formed from multiple layers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] 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.
[0019] The techniques of the present invention can readily be
understood by considering the following detailed description in
conjunction with the accompanying drawings, in which:
[0020] FIG. 1 illustrates a flow chart illustrating a method for
fabricating a DRAM capacitor stack in accordance with some
embodiments.
[0021] FIGS. 2A and 2B illustrate simplified cross-sectional views
of a DRAM capacitor stack fabricated in accordance with some
embodiments.
[0022] FIG. 3 illustrates a simplified cross-sectional view of a
DRAM memory cell fabricated in accordance with some
embodiments.
[0023] FIG. 4 illustrates a simplified cross-sectional view of a
DRAM memory cell fabricated in accordance with some
embodiments.
DETAILED DESCRIPTION
[0024] 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.
[0025] 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.
[0026] 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%.
[0027] As used herein, the term "substantially" generally refers to
.+-.5% of a stated value.
[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] 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).
[0030] The term "substrate" as used herein may refer to any
workpiece on which formation or treatment of material layers is
desired. Non-limiting examples include silicon, germanium, silica,
sapphire, zinc oxide, silicon carbide, aluminum nitride, gallium
nitride, Spinel, silicon on oxide, silicon carbide on oxide, glass,
gallium nitride, indium nitride, aluminum nitride, glasses,
combinations or alloys thereof, and other solid materials.
[0031] As used herein, the notation "Mo--O" and "MoO" and
"MoO.sub.x" will be understood to be equivalent and will be used
interchangeably and will be understood to include a material
containing these elements in any ratio. Where a specific
composition is discussed, the atomic concentrations (or ranges)
will be provided. The notation is extendable to other materials and
other elemental combinations (e.g. Mo--O--N, MoON, MoON.sub.x,
etc.) discussed herein.
[0032] As used herein, the terms "film" and "layer" will be
understood to represent a portion of a stack. They will be
understood to cover both a single layer as well as a multilayered
structure (i.e. a nanolaminate). As used herein, these terms will
be used synonymously and will be considered equivalent.
[0033] As used herein, the term "between" (when used with a range
of values) will be understood to mean that both boundary values and
any value between the boundaries can be within the scope of the
range.
[0034] As used herein, the terms "first," "second," and other
ordinals will be understood to provide differentiation only, rather
than imposing any specific spatial or temporal order.
[0035] As used herein, the term "oxide" (of an element) will be
understood to include additional components besides the element and
oxygen, including but not limited to a dopant or alloy.
[0036] As used herein, the term "nitride" (of an element) will be
understood to include additional components besides the element and
nitrogen, including but not limited to a dopant or alloy.
[0037] Dopants can be added to the dielectric material to increase
the k-value and/or decrease the leakage current. 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. The
concentration of the dopant is one factor that affects the
crystallinity of the dielectric material. Other factors that affect
the crystallinity of the dielectric material comprise annealing
time, annealing temperature, film thickness, etc. Generally, as the
concentration of the dopant is increased, the crystallization
temperature of the dielectric material increases.
[0038] Dopants can be added to the electrode material to alter the
resistivity and/or influence the crystallinity. 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. The concentration
of the dopant is one factor that affects the crystallinity of the
dielectric material. Other factors that affect the crystallinity of
the electrode material comprise annealing time, annealing
temperature, film thickness, etc.
[0039] The term "nanolaminate", as used herein, will be understood
to be defined as a material or layer that is formed from the
deposition of a plurality of sub-layers. Typically, the sub-layers
include different materials and the different sub-layers are
alternated in a predetermined ratio of thicknesses and/or
compositions.
[0040] As used herein, the term "flash layer" will be understood to
describe an additional layer inserted between the first (e.g.
bottom) electrode layer and the dielectric layer.
[0041] As used herein, the term "capping layer" will be understood
to describe an additional layer inserted between the second (e.g.
top) electrode layer and the dielectric layer.
[0042] As used herein, the term "blocking layer" will be understood
to describe an additional generic layer inserted either between the
first (e.g. bottom) electrode layer and the dielectric layer,
between the second (e.g. top) electrode layer and the dielectric
layer, or both. As defined above, both "flash layers" and "capping
layers" are examples of the more general "blocking layer".
[0043] As used herein, the term "inert gas" will be understood to
include noble gases (He, Ne, Ar, Kr, Xe) and, unless the text or
context excludes it (e.g., by describing nitride formation as
undesirable), nitrogen (N.sub.2).
[0044] As used herein, the term "monolayer" will be understood to
include a single layer of atoms or molecules covering a surface,
with substantially all available bonding sites satisfied and
substantially all individual members of the adsorbed species in
direct physical contact with the underlying surface.
[0045] As used herein, the term "sub-monolayer" or "pre-wetting
layer" will be understood to include a partial or incomplete
monolayer; maximum thickness is one atom or molecule, but not all
available bonding sites on the surface are covered, so that the
average thickness is less than one atom or molecule.
[0046] As used herein, the term "Surface" will be understood to
describe the boundary between the ambient environment and a feature
of the substrate.
[0047] DRAM capacitor stacks are formed from a number of deposited
thin films. 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
the desired composition and crystalline phase of the thin film. The
thin films used to form the MIM DRAM capacitor stack may be formed
using any common 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 materials discussed below. Those
skilled in the art will appreciate that the teachings described
below are not limited by the technology used for the deposition
process.
[0048] In FIGS. 2-4 below, a capacitor stack is illustrated using a
simple planar structure. Those skilled in the art will appreciate
that the description and teachings to follow 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 invention.
[0049] Leakage current in capacitor dielectric materials can be due
to Schottky emission, Frenkel-Poole defects (e.g. oxygen vacancies
(V.sub.ox) or grain boundaries), or Fowler-Nordheim tunneling.
Schottky emission, also called thermionic emission, is a common
mechanism and is the thermally activated flow of charge over an
energy barrier whereby the effective barrier height of a MIM
capacitor controls leakage current. The nominal barrier height is a
function of the difference between the work function of the
electrode and the electron affinity of the dielectric. The electron
affinity of a dielectric is closely related to the conduction band
offset of the dielectric. The Schottky emission behavior of a
dielectric layer is generally determined by the properties of the
dielectric/electrode interface. Frenkel-Poole emission allows the
conduction of charges through a dielectric layer through the
interaction with defect sites such as vacancies, grain boundaries,
and the like. As such, the Frenkel-Poole emission behavior of a
dielectric layer is generally determined by the dielectric layer's
bulk properties. Fowler-Nordheim emission allows the conduction of
charges through a dielectric layer through direct tunneling without
any intermediary interaction with e.g. defects. As such, the
Fowler-Nordheim emission behavior of a dielectric layer is
generally determined by the physical thickness of the dielectric
layer. This leakage current is a primary driving force in the
adoption of high-k dielectric materials. The use of high-k
materials allows the physical thickness of the dielectric layer to
be as thick as possible while maintaining the required capacitance
(see Eqn 1 above).
[0050] The mechanisms for charge transport discussed above suggest
that there are several parameters that influence the leakage
current across the metal-dielectric interface. Examples of the
parameters include physical thickness of the dielectric material,
the band gap of the dielectric material, the work function of the
metal, the Schottky barrier height (SBH) between the metal and the
dielectric material, etc. The SBH has been found to be influenced
by many variables such as the composition of the metal and the
dielectric, doping levels, defect densities, processing conditions,
etc.
[0051] As discussed previously, conductive metal oxide materials
such as molybdenum oxide are candidates for electrode materials due
to their high work function values. Additionally, they have crystal
structures that are generally complimentary to those of high k
dielectric materials (e.g. the rutile phase of titanium oxide).
Transition metals such as molybdenum can exist in a number of
valence states. As an example, the molybdenum in MoO.sub.2 is in
the +4 valence state and the molybdenum in MoO.sub.3 is in the +6
valence state. For very thin molybdenum oxide films (i.e. <about
10 nm), it is difficult to precisely control the Mo:O atomic ratio.
This leads to a higher resistance material which may not meet the
resistivity and device speed requirements for future DRAM devices.
Typically, molybdenum oxide is present as MoO.sub.3 (or more
generally MoO.sub.2+x) after deposition. The film may be treated to
convert the MoO.sub.3 to conductive MoO.sub.2. When used as the
first (e.g. bottom) electrode in the capacitor stack, this
treatment may include a thermal anneal treatment. This anneal
treatment serves to convert the MoO.sub.3 to MoO.sub.2 and to
crystallize the MoO.sub.2 before the dielectric layer is deposited
above the first electrode.
[0052] The integration of molybdenum oxide as a second electrode
(e.g. top) layer has been difficult. The thermal treatments
employed to the first electrode that convert the MoO.sub.3 to
MoO.sub.2 and to crystallize the MoO.sub.2 may have a negative
impact on the performance of the dielectric layer. Typically, an
"oxygen sink" must be employed to scavenge the excess oxygen
without impacting the underlying dielectric layer. In some
embodiments, one or more dopants are added to the molybdenum oxide
to alter the crystallinity. Some materials that are attractive as
dopants for molybdenum oxide comprise elements Group-4 (e.g. Ti,
Zr, Hf) of the periodic table (using the new IUPAC designations).
These elements may be incorporated into the molybdenum oxide as
either the metal oxide (e.g. titanium oxide) or as the metal
nitride (e.g. titanium nitride).
[0053] FIG. 1 describes a method, 100, for fabricating a DRAM
capacitor stack. The initial step, 102, includes forming a first
electrode material above a substrate, wherein the first electrode
material comprises a metal element. Examples of suitable electrode
materials comprise metals, conductive metal oxides, conductive
metal silicides, conductive metal nitrides, and combinations
thereof. Particularly interesting classes of materials include the
conductive metal oxides and the conductive metal nitrides. The next
step, 104, includes forming a dielectric material above the first
electrode material. Optionally, the dielectric material 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. The next step, 106, includes forming a second
electrode material above the dielectric material, wherein the
second electrode material comprises a metal element. Examples of
suitable second electrode materials comprise metals, conductive
metal oxides, conductive metal silicides, conductive metal
nitrides, and combinations thereof. A particularly interesting
class of materials is the conductive metal oxides. The second
electrode material is formed with one or more dopants added that
alter the work function, crystallinity, and/or the resistivity of
the second electrode material. The dopants may be uniformly
distributed throughout the second electrode material or may be
distributed with a gradient in their concentration profile. In some
embodiments, the second electrode material is formed from layers of
different materials. As an example, the second electrode material
may be formed from a metal or conductive metal nitride and a
conductive metal oxide. Optionally, the capacitor stack can then be
subjected to PMA treatment process (not shown). Examples of the PDA
and PMA treatments are further described in U.S. patent application
Ser. No. 13/159,842 (now U.S. Pat. No. 8,815,677) filed on Jun. 14,
2011, which is herein incorporated by reference for all
purposes.
[0054] In some embodiments wherein the dopants are distributed
throughout the second electrode material with a gradient in their
concentration profile, it may be advantageous to distribute the
dopant such that the concentration of the dopant is lowest at the
second electrode material/dielectric material interface. This
distribution will decrease the amount of the dopant that may
diffuse into the dielectric material during subsequent anneal
steps. Some dopants may negatively impact the performance of the
dielectric material (i.e. lower the k-value, increase the EOT
performance, increase the leakage current, etc.).
[0055] The dopants may be added to the second electrode material by
introducing the dopant species during the formation of the second
electrode material. Typically, the second electrode materials are
formed using ALD or CVD technologies. In these cases, precursors
containing the dopant atoms may be introduced during the process
sequence of the ALD or CVD deposition step. The dopants may be
metals, metal oxides, metal nitrides, metal silicides, metal
carbides, non-metals, halogens, or combinations thereof (i.e.
metal-silicon-nitride, or metal-silicon-oxygen-nitride, etc). The
metal oxides, metal nitrides, metal silicides, metal carbides, and
combinations may be suitable as dopants because many of these
compounds are conductive, and as such, may advantageously alter the
work function, crystallinity, and/or resistivity of the electrode
material. The dopants may be added individually or may be added in
combination. The dopants may be uniformly distributed throughout
the second electrode material or may be distributed with a gradient
in their concentration profile. The dopants may be added to a
concentration that will not negatively impact the ability of the
second electrode material to form the desired crystalline phase.
The maximum doping concentration will vary depending on the dopant
material and subsequent anneal conditions. Generally, the doping
concentration is chosen such that it does not prevent the second
electrode from crystallizing during the subsequent anneal step. As
used herein, the second electrode material will be considered to be
crystallized if it is .gtoreq.30% crystalline after the anneal as
determined by techniques such as x-ray diffraction (XRD).
[0056] In some embodiments, dopants including titanium oxide are
added to a second electrode material that includes molybdenum
oxide. In some embodiments, the dopants are added in a range
between about 1 atomic % and about 20 atomic %, such as between
about 5 atomic % and about 15 atomic %. Without being limited by
theory, it is believed that the titanium oxide serves two purposes
as a dopant within the molybdenum oxide. Firstly, the titanium
oxide may serve as an "oxygen sink" and scavenge oxygen from the
molybdenum oxide as it is converted from MoO.sub.3 to MoO.sub.2.
Secondly, the titanium oxide may exist in a rutile crystal
structure. Molybdenum oxide may also exist as a distorted rutile
crystal structure. Therefore, the titanium oxide may serve to
promote the crystallization of the molybdenum oxide during
subsequent anneal treatments. This may allow the molybdenum oxide
to be crystallized at lower temperatures that will not negatively
affect performance of the underlying dielectric materials.
[0057] In some embodiments, dopants including titanium nitride are
added to a second electrode material that includes molybdenum
oxide. In some embodiments, the dopants are added in a range
between about 1 atomic % and about 20 atomic %, such as between
about 5 atomic % and about 15 atomic %. Without being limited by
theory, it is believed that the titanium nitride serves two
purposes as a dopant within the molybdenum oxide. Firstly, the
titanium nitride may serve as an "oxygen sink" and scavenge oxygen
from the molybdenum oxide as it is converted from MoO.sub.3 to
MoO.sub.2. Secondly, the titanium nitride may exist in a cubic
crystal structure. Molybdenum oxide may exist as a distorted rutile
crystal structure. Molybdenum oxide in the form of MoO.sub.2 forms
readily on titanium nitride. Therefore, the titanium nitride may
serve to promote the crystallization of the molybdenum oxide during
subsequent anneal treatments. This may allow the molybdenum oxide
to be crystallized at lower temperatures that will not negatively
affect performance of the underlying dielectric materials.
[0058] FIG. 2A illustrates a simple capacitor stack, 200,
consistent with some embodiments. Using the method as outlined in
FIG. 1 and described above, first electrode material, 202, is
formed above substrate, 201. Generally, the substrate has already
received several processing steps in the manufacture of a full DRAM
device. First electrode material, 202, comprises one of metals,
conductive metal oxides, conductive metal nitrides, conductive
metal silicides, etc. In some embodiments, the first electrode
material is a conductive metal oxide. The first electrode material,
502, can be annealed to crystallize the material.
[0059] In the next step, dielectric material, 204, would then be
formed above the first electrode material, 202. A wide variety of
dielectric materials have been targeted for use in DRAM capacitors.
Examples of suitable dielectric materials comprise 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. 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 zirconium
oxide. Typically, dielectric material, 204, is subjected to a PDA
treatment before the formation of the second electrode material as
mentioned earlier.
[0060] In the next step, the second electrode material, 206, is
formed above dielectric material, 204. The second electrode
material comprises one of metals, conductive metal oxides,
conductive metal nitrides, conductive metal silicides, conductive
metal carbides, etc. The second electrode material is formed with
one or more dopants added that alter the work function,
crystallinity, and/or the resistivity of the second electrode
material. The dopants may be uniformly distributed throughout the
second electrode material or may be distributed with a gradient in
their concentration profile.
[0061] Dopants may be added to the second electrode material to
alter properties such as the work function, crystallinity, and/or
the resistivity. The dopants may be added to the second electrode
material by introducing the dopant species during the formation of
the second electrode material. Typically, the second electrode
materials are formed using ALD or CVD technologies. In these cases,
precursors containing the dopant atoms may be introduced during the
process sequence of the ALD or CVD deposition step. The dopants may
be metals, metal oxides, metal nitrides, metal silicides, metal
carbides, non-metals, halogens, or combinations thereof (i.e.
metal-silicon-nitride, or metal-silicon-oxygen-nitride, etc). The
metal oxides, metal nitrides, metal silicides, metal carbides, and
combinations may be suitable as dopants because many of these
compounds are conductive, and as such, may advantageously alter the
work function, crystallinity, and/or resistivity of the electrode
material. The dopants may be added individually or may be added in
combination. The dopants may be uniformly distributed throughout
the second electrode material or may be distributed with a gradient
in their concentration profile. A second class of dopants may be
added to the second electrode material to alter the resistivity.
The dopants may be metals, metal oxides, metal nitrides, metal
silicides, metal carbides, non-metals, halogens, or combinations
thereof (i.e. metal-silicon-nitride, or
metal-silicon-oxygen-nitride, etc). The metal oxides, metal
nitrides, metal silicides, metal carbides, and combinations may be
suitable as dopants because many of these compounds are conductive,
and as such, may advantageously alter the work function,
crystallinity, and/or resistivity of the electrode material. The
dopants may be added individually or may be added in combination.
The dopants may be uniformly distributed throughout the second
electrode material or may be distributed with a gradient in their
concentration profile. The maximum doping concentration will vary
depending on the dopant material and subsequent anneal conditions.
Generally, the doping concentration is chosen such that it does not
prevent the second electrode material from crystallizing during the
subsequent anneal step. As used herein, the second electrode
material will be considered to be crystallized if it is .gtoreq.30%
crystalline after the anneal as determined by techniques such as
x-ray diffraction (XRD). Typically, the capacitor stack would then
be subjected to a PMA treatment. The doped second electrode
material may contribute in lowering the leakage current of the
capacitor stack.
[0062] In some embodiments, dopants including titanium oxide are
added to a second electrode material that includes molybdenum
oxide. In some embodiments, the dopants are added in a range
between about 1 atomic % and about 20 atomic %, such as between
about 5 atomic % and about 15 atomic %. Without being limited by
theory, it is believed that the titanium oxide serves two purposes
as a dopant within the molybdenum oxide. Firstly, the titanium
oxide may serve as an "oxygen sink" and scavenge oxygen from the
molybdenum oxide as it is converted from MoO.sub.3 to MoO.sub.2.
Secondly, the titanium oxide may exist in a rutile crystal
structure. Molybdenum oxide may also exist as a distorted rutile
crystal structure. Therefore, the titanium oxide may serve to
promote the crystallization of the molybdenum oxide during
subsequent anneal treatments. This may allow the molybdenum oxide
to be crystallized at lower temperatures that will not negatively
affect performance of the underlying dielectric materials.
[0063] In some embodiments, dopants including titanium nitride are
added to a second electrode material that includes molybdenum
oxide. In some embodiments, the dopants are added in a range
between about 1 atomic % and about 20 atomic %, such as between
about 5 atomic % and about 15 atomic %. Without being limited by
theory, it is believed that the titanium nitride serves two
purposes as a dopant within the molybdenum oxide. Firstly, the
titanium nitride may serve as an "oxygen sink" and scavenge oxygen
from the molybdenum oxide as it is converted from MoO.sub.3 to
MoO.sub.2. Secondly, the titanium nitride may exist in a cubic
crystal structure. Molybdenum oxide may exist as a distorted rutile
crystal structure. Molybdenum oxide in the form of MoO.sub.2 forms
readily on titanium nitride. Therefore, the titanium nitride may
serve to promote the crystallization of the molybdenum oxide during
subsequent anneal treatments. This may allow the molybdenum oxide
to be crystallized at lower temperatures that will not negatively
affect performance of the underlying dielectric materials.
[0064] FIG. 2B illustrates a simple capacitor stack, 208,
consistent with some embodiments. Using the method as outlined in
FIG. 1 and described above, first electrode material, 210, is
formed above substrate, 201. Generally, the substrate has already
received several processing steps in the manufacture of a full DRAM
device. First electrode material, 210, comprises one of metals,
conductive metal oxides, conductive metal nitrides, conductive
metal silicides, etc. In some embodiments, the first electrode
material is a conductive metal oxide. The first electrode material,
210, can be annealed to crystallize the material.
[0065] In the next step, dielectric material, 212, would then be
formed above the first electrode material, 210. A wide variety of
dielectric materials have been targeted for use in DRAM capacitors.
Examples of suitable dielectric materials comprise 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. 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 zirconium
oxide. Typically, dielectric material, 212, is subjected to a PDA
treatment before the formation of the second electrode material as
mentioned earlier.
[0066] In the next step, the second electrode structure is
comprised of multiple layers of material. The third material layer,
214, is formed above dielectric material, 212. The third material
layer comprises one of metals, conductive metal oxides, conductive
metal nitrides, conductive metal silicides, conductive metal
carbides, etc. The third material layer additionally comprises one
or more dopants added that alter the work function, crystallinity,
and/or the resistivity of the third material layer. The dopants may
be uniformly distributed throughout the third material layer or may
be distributed with a gradient in their concentration profile.
Fourth material layer, 216, is formed above third material layer,
214, and comprises one of metals, conductive metal oxides,
conductive metal nitrides, conductive metal silicides, etc.
Optionally, the fourth material layer, 216, can be doped as
discussed below. The purpose of this layer is to provide high
conductivity to the second electrode structure. In some
embodiments, the fourth material layer is a metal or a conductive
metal nitride.
[0067] Dopants may be added to the second electrode structure
materials to alter properties such as the work function,
crystallinity, and/or the resistivity. The dopants may be added to
the second electrode structure materials by introducing the dopant
species during the formation of the second electrode structure
materials. Typically, the second electrode structure materials are
formed using ALD or CVD technologies. In these cases, precursors
containing the dopant atoms may be introduced during the process
sequence of the ALD or CVD deposition step. The dopants may be
metals, metal oxides, metal nitrides, metal silicides, metal
carbides, non-metals, halogens, or combinations thereof (i.e.
metal-silicon-nitride, or metal-silicon-oxygen-nitride, etc). The
metal oxides, metal nitrides, metal silicides, metal carbides, and
combinations may be suitable as dopants because many of these
compounds are conductive, and as such, may advantageously alter the
work function, crystallinity, and/or resistivity of the electrode
material. The dopants may be added individually or may be added in
combination. The dopants may be uniformly distributed throughout
the second electrode structure materials or may be distributed with
a gradient in their concentration profile. A second class of
dopants may be added to the second electrode material to alter the
resistivity. The dopants may be metals, metal oxides, metal
nitrides, metal silicides, metal carbides, non-metals, halogens, or
combinations thereof (i.e. metal-silicon-nitride, or
metal-silicon-oxygen-nitride, etc). The metal oxides, metal
nitrides, metal silicides, metal carbides, and combinations may be
suitable as dopants because many of these compounds are conductive,
and as such, may advantageously alter the work function,
crystallinity, and/or resistivity of the electrode material. The
dopants may be added individually or may be added in combination.
The dopants may be uniformly distributed throughout the second
electrode structure materials or may be distributed with a gradient
in their concentration profile. The maximum doping concentration
will vary depending on the dopant material and subsequent anneal
conditions. Generally, the doping concentration is chosen such that
it does not prevent the second electrode structure materials from
crystallizing during the subsequent anneal step. As used herein,
the second electrode structure materials will be considered to be
crystallized if they are .gtoreq.30% crystalline after the anneal
as determined by techniques such as x-ray diffraction (XRD).
Typically, the capacitor stack would then be subjected to a PMA
treatment. The doped second electrode structure may contribute in
lowering the leakage current of the capacitor stack.
[0068] In some embodiments, dopants including titanium oxide are
added to a second electrode material that includes molybdenum
oxide. In some embodiments, the dopants are added in a range
between about 1 atomic % and about 20 atomic %, such as between
about 5 atomic % and about 15 atomic %. Without being limited by
theory, it is believed that the titanium oxide serves two purposes
as a dopant within the molybdenum oxide. Firstly, the titanium
oxide may serve as an "oxygen sink" and scavenge oxygen from the
molybdenum oxide as it is converted from MoO.sub.3 to MoO.sub.2.
Secondly, the titanium oxide may exist in a rutile crystal
structure. Molybdenum oxide may also exist as a distorted rutile
crystal structure. Therefore, the titanium oxide may serve to
promote the crystallization of the molybdenum oxide during
subsequent anneal treatments. This may allow the molybdenum oxide
to be crystallized at lower temperatures that will not negatively
affect performance of the underlying dielectric materials.
[0069] In some embodiments, dopants including titanium nitride are
added to a second electrode material that includes molybdenum
oxide. In some embodiments, the dopants are added in a range
between about 1 atomic % and about 20 atomic %, such as between
about 5 atomic % and about 15 atomic %. Without being limited by
theory, it is believed that the titanium nitride serves two
purposes as a dopant within the molybdenum oxide. Firstly, the
titanium nitride may serve as an "oxygen sink" and scavenge oxygen
from the molybdenum oxide as it is converted from MoO.sub.3 to
MoO.sub.2. Secondly, the titanium nitride may exist in a cubic
crystal structure. Molybdenum oxide may exist as a distorted rutile
crystal structure. Molybdenum oxide in the form of MoO.sub.2 forms
readily on titanium nitride. Therefore, the titanium nitride may
serve to promote the crystallization of the molybdenum oxide during
subsequent anneal treatments. This may allow the molybdenum oxide
to be crystallized at lower temperatures that will not negatively
affect performance of the underlying dielectric materials.
[0070] In some embodiments, a first electrode material, 202,
comprising between about 3 nm and about 15 nm of molybdenum oxide
is formed above a substrate, 201. The molybdenum oxide electrode
material is formed at a process temperature between about 125 C and
about 400 C using an ALD process technology. Optionally, the
substrate with the first electrode material is then annealed in an
inert or reducing atmosphere comprising between about 1% and about
10% H.sub.2 in N.sub.2 or other inert gases and advantageously
between about 5% and about 10% H.sub.2 in N.sub.2 or other inert
gases between about 300 C and about 650 C for between about 1
millisecond and about 60 minutes.
[0071] In the next step, dielectric material, 204, would then be
formed above the annealed first electrode material, 202. A wide
variety of dielectric materials have been targeted for use in DRAM
capacitors. Examples of suitable dielectric materials comprise
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. 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, dielectric material, 204, is subjected to a
PDA treatment before the formation of the second electrode as
discussed previously. A specific dielectric material of interest is
titanium oxide doped with aluminum to between about 5 atomic % and
about 15 atomic % aluminum. The rutile phase of titanium oxide will
form preferentially on the underlying doped molybdenum oxide
electrode resulting in a higher k value.
[0072] In a specific example, the dielectric material comprises
between about 4 nm to about 10 nm of titanium oxide wherein at
least 30% of the titanium oxide is present in the rutile phase
after an anneal treatment. Generally, the titanium oxide dielectric
material may either be a single film or may comprise a
nanolaminate. Advantageously, the titanium oxide material is doped
with aluminum at a concentration between about 5 atomic % and about
15 atomic % aluminum. The titanium oxide dielectric material is
formed at a process temperature between about 200 C and 350 C using
an ALD process technology. The substrate with the first electrode
material and dielectric material 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 300 C to
about 650 C for between about 1 millisecond to about 60
minutes.
[0073] In a specific example, the dielectric material comprises
between about 4 nm to about 10 nm of zirconium oxide wherein at
least 30% of the zirconium oxide is present in the tetragonal phase
after an anneal treatment. Generally, the zirconium oxide
dielectric material may either be a single film or may comprise a
nanolaminate. Advantageously, the zirconium oxide material is doped
with aluminum at a concentration between about 5 atomic % and about
15 atomic % aluminum. The zirconium oxide dielectric material is
formed at a process temperature between about 200 C and 350 C using
an ALD process technology. The substrate with the first electrode
material and dielectric material 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 300 C to
about 650 C for between about 1 millisecond to about 60
minutes.
[0074] Second electrode material, 206, is then formed above
dielectric material, 204. The second electrode is typically a metal
such as ruthenium, platinum, titanium nitride, tantalum nitride,
titanium-aluminum-nitride, tungsten, tungsten nitride, molybdenum,
molybdenum oxide, molybdenum nitride, vanadium nitride, or others.
Advantageously, the second electrode material is molybdenum oxide.
The second electrode material is typically between about 3 nm and
50 nm in thickness. As discussed previously, the second electrode
material may also be doped with one or more dopants to alter the
work function, crystallinity, and/or the resistivity of the second
electrode material as described previously.
[0075] In some embodiments, dopants including titanium oxide are
added to a second electrode material that includes molybdenum
oxide. In some embodiments, the dopants are added in a range
between about 1 atomic % and about 20 atomic %, such as between
about 5 atomic % and about 15 atomic %. Without being limited by
theory, it is believed that the titanium oxide serves two purposes
as a dopant within the molybdenum oxide. Firstly, the titanium
oxide may serve as an "oxygen sink" and scavenge oxygen from the
molybdenum oxide as it is converted from MoO.sub.3 to MoO.sub.2.
Secondly, the titanium oxide may exist in a rutile crystal
structure. Molybdenum oxide may also exist as a distorted rutile
crystal structure. Therefore, the titanium oxide may serve to
promote the crystallization of the molybdenum oxide during
subsequent anneal treatments. This may allow the molybdenum oxide
to be crystallized at lower temperatures that will not negatively
affect performance of the underlying dielectric materials.
[0076] In some embodiments, dopants including titanium nitride are
added to a second electrode material that includes molybdenum
oxide. In some embodiments, the dopants are added in a range
between about 1 atomic % and about 20 atomic %, such as between
about 5 atomic % and about 15 atomic %. Without being limited by
theory, it is believed that the titanium nitride serves two
purposes as a dopant within the molybdenum oxide. Firstly, the
titanium nitride may serve as an "oxygen sink" and scavenge oxygen
from the molybdenum oxide as it is converted from MoO.sub.3 to
MoO.sub.2. Secondly, the titanium nitride may exist in a cubic
crystal structure. Molybdenum oxide may exist as a distorted rutile
crystal structure. Molybdenum oxide in the form of MoO.sub.2 forms
readily on titanium nitride. Therefore, the titanium nitride may
serve to promote the crystallization of the molybdenum oxide during
subsequent anneal treatments. This may allow the molybdenum oxide
to be crystallized at lower temperatures that will not negatively
affect performance of the underlying dielectric materials.
[0077] Typically, the capacitor stack is then subjected to a post
metallization anneal (PMA) treatment. The PMA treatment serves to
crystallize the second electrode material and to anneal defects and
interface states that are formed at the dielectric/second electrode
interface during the deposition. The doped second electrode
material may contribute in lowering the leakage current of the
capacitor stack.
[0078] Using the method as outlined in FIG. 1 and described above,
first electrode material, 210, is formed above substrate, 201.
Generally, the substrate has already received several processing
steps in the manufacture of a full DRAM device. First electrode
material, 210, comprises one of metals, conductive metal oxides,
conductive metal nitrides, conductive metal silicides, etc. In some
embodiments, the first electrode material is a conductive metal
oxide. The first electrode material, 210, can be annealed to
crystallize the material.
[0079] In the next step, dielectric material, 212, would then be
formed above the first electrode material, 210. A wide variety of
dielectric materials have been targeted for use in DRAM capacitors.
Examples of suitable dielectric materials comprise 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. 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 zirconium
oxide. Typically, dielectric material, 212, is subjected to a PDA
treatment before the formation of the second electrode material as
mentioned earlier.
[0080] In a specific example, the dielectric material comprises
between about 4 nm to about 10 nm of titanium oxide wherein at
least 30% of the titanium oxide is present in the rutile phase
after an anneal treatment. Generally, the titanium oxide dielectric
material may either be a single film or may comprise a
nanolaminate. Advantageously, the titanium oxide material is doped
with aluminum at a concentration between about 5 atomic % and about
15 atomic % aluminum. The titanium oxide dielectric material is
formed at a process temperature between about 200 C and 350 C using
an ALD process technology. The substrate with the first electrode
structure and dielectric material 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 300 C to
about 650 C for between about 1 millisecond to about 60
minutes.
[0081] In a specific example, the dielectric material comprises
between about 4 nm to about 10 nm of zirconium oxide wherein at
least 30% of the zirconium oxide is present in the tetragonal phase
after an anneal treatment. Generally, the zirconium oxide
dielectric material may either be a single film or may comprise a
nanolaminate. Advantageously, the zirconium oxide material is doped
with aluminum at a concentration between about 5 atomic % and about
15 atomic % aluminum. The zirconium oxide dielectric material is
formed at a process temperature between about 200 C and 350 C using
an ALD process technology. The substrate with the first electrode
structure and dielectric material 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 300 C to
about 650 C for between about 1 millisecond to about 60
minutes.
[0082] In the next step, the second electrode structure is
comprised of multiple layers of material. The third material layer,
214, is formed above dielectric material, 212. The third material
layer comprises one of metals, conductive metal oxides, conductive
metal nitrides, conductive metal silicides, conductive metal
carbides, etc. More specifically, in some embodiments, third
electrode material, 214, comprises conductive metal compounds of
molybdenum oxide. The third material layer additionally comprises
one or more dopants added that alter the work function,
crystallinity, and/or the resistivity of the third material layer.
The dopants may be uniformly distributed throughout the third
material layer or may be distributed with a gradient in their
concentration profile. Fourth material layer, 216, is formed above
third material layer, 214, and comprises one of metals, conductive
metal oxides, conductive metal nitrides, conductive metal
silicides, etc. In one example, fourth material layer, 216,
comprises titanium nitride. Optionally, the fourth material layer,
216, can be doped as discussed below. The purpose of this layer is
to provide high conductivity to the second electrode structure. In
some embodiments, the fourth material layer is a metal or a
conductive metal nitride.
[0083] Dopants may be added to the second electrode structure
materials to alter properties such as the work function,
crystallinity, and the resistivity. In some embodiments, the
dopants are added in a range between about 1 atomic % and about 20
atomic %, such as between about 5 atomic % and about 15 atomic %.
The dopants may be added to the second electrode structure
materials by introducing the dopant species during the formation of
the second electrode structure materials. Typically, the second
electrode structure materials are formed using ALD or CVD
technologies. In these cases, precursors containing the dopant
atoms may be introduced during the process sequence of the ALD or
CVD deposition step. The dopants may be metals, metal oxides, metal
nitrides, metal silicides, metal carbides, non-metals, halogens, or
combinations thereof (i.e. metal-silicon-nitride, or
metal-silicon-oxygen-nitride, etc). The metal oxides, metal
nitrides, metal silicides, metal carbides, and combinations may be
suitable as dopants because many of these compounds are conductive,
and as such, may advantageously alter the work function,
crystallinity, and/or resistivity of the electrode material. The
dopants may be added individually or may be added in combination.
The dopants may be uniformly distributed throughout the second
electrode structure materials or may be distributed with a gradient
in their concentration profile. A second class of dopants may be
added to the second electrode materials to alter the resistivity.
The dopants may be metals, metal oxides, metal nitrides, metal
silicides, metal carbides, non-metals, halogens, or combinations
thereof (i.e. metal-silicon-nitride, or
metal-silicon-oxygen-nitride, etc). The metal oxides, metal
nitrides, metal silicides, metal carbides, and combinations may be
suitable as dopants because many of these compounds are conductive,
and as such, may advantageously alter the work function,
crystallinity, and/or resistivity of the electrode material. The
dopants may be added individually or may be added in combination.
The dopants may be uniformly distributed throughout the second
electrode structure materials or may be distributed with a gradient
in their concentration profile. The maximum doping concentration
will vary depending on the dopant material and subsequent anneal
conditions. Generally, the doping concentration is chosen such that
it does not prevent the second electrode structure materials from
crystallizing during the subsequent anneal step. As used herein,
the second electrode structure materials will be considered to be
crystallized if they are .gtoreq.30% crystalline after the anneal
as determined by techniques such as x-ray diffraction (XRD).
Typically, the capacitor stack would then be subjected to a PMA
treatment.
[0084] In some embodiments, a fourth electrode material comprising
about 50 nm of titanium nitride is formed above a third electrode
material comprising between about 5 nm and about 20 nm of
molybdenum oxide. These thicknesses are used as examples. Future
DRAM devices will require molybdenum oxide thickness of about 2 nm
to 3 nm and titanium nitride thicknesses of about 2 nm to 3 nm. The
total thickness of the second electrode structure for future DRAM
devices will be about 6 nm. The molybdenum oxide electrode material
is formed at a process temperature between about 125 C and about
400 C using an ALD process technology. One or more dopants are
added to the molybdenum oxide which alter the work function,
crystallinity, and/or the resistivity. Examples of suitable dopants
comprise titanium, zirconium, hafnium, or combinations thereof.
Typically, the capacitor stack would then be subjected to a PMA
treatment.
[0085] In some embodiments, dopants including titanium oxide are
added to a second electrode material that includes molybdenum
oxide. In some embodiments, the dopants are added in a range
between about 1 atomic % and about 20 atomic %, such as between
about 5 atomic % and about 15 atomic %. Without being limited by
theory, it is believed that the titanium oxide serves two purposes
as a dopant within the molybdenum oxide. Firstly, the titanium
oxide may serve as an "oxygen sink" and scavenge oxygen from the
molybdenum oxide as it is converted from MoO.sub.3 to MoO.sub.2.
Secondly, the titanium oxide may exist in a rutile crystal
structure. Molybdenum oxide may also exist as a distorted rutile
crystal structure. Therefore, the titanium oxide may serve to
promote the crystallization of the molybdenum oxide during
subsequent anneal treatments. This may allow the molybdenum oxide
to be crystallized at lower temperatures that will not negatively
affect performance of the underlying dielectric materials.
[0086] In some embodiments, dopants including titanium nitride are
added to a second electrode material that includes molybdenum
oxide. In some embodiments, the dopants are added in a range
between about 1 atomic % and about 20 atomic %, such as between
about 5 atomic % and about 15 atomic %. Without being limited by
theory, it is believed that the titanium nitride serves two
purposes as a dopant within the molybdenum oxide. Firstly, the
titanium nitride may serve as an "oxygen sink" and scavenge oxygen
from the molybdenum oxide as it is converted from MoO.sub.3 to
MoO.sub.2. Secondly, the titanium nitride may exist in a cubic
crystal structure. Molybdenum oxide may exist as a distorted rutile
crystal structure. Molybdenum oxide in the form of MoO.sub.2 forms
readily on titanium nitride. Therefore, the titanium nitride may
serve to promote the crystallization of the molybdenum oxide during
subsequent anneal treatments. This may allow the molybdenum oxide
to be crystallized at lower temperatures that will not negatively
affect performance of the underlying dielectric materials.
[0087] 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. 3 is used
to illustrate one DRAM cell, 320, manufactured using a doped first
electrode structure as discussed previously. The cell, 320, is
illustrated schematically to include two principle components, a
cell capacitor, 300, and a cell transistor, 302. The cell
transistor is usually constituted by a MOS transistor having a
gate, 314, source, 310, and drain, 312. 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 and an upper or plate electrode. 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.
[0088] As was described previously, the cell capacitor, 300,
comprises a first electrode, 304, formed on substrate, 301. The
first electrode, 304, is connected to the source or drain of the
cell transistor, 302. For illustrative purposes, the first
electrode has been connected to the source, 310, in this example.
For the purposes of illustration, first electrode material, 304,
will be crystalline MoO.sub.2 in this example as described
previously. The first electrode material may contribute in lowering
the leakage current of the capacitor stack. As discussed
previously, first electrode material, 304, may be subjected to an
anneal in an inert or reducing atmosphere before the formation of
the dielectric material to crystallize the MoO.sub.2 and to reduce
any MoO.sub.2+x compounds that may have formed during the formation
of the first electrode material. Dielectric material, 306, is
formed above the first electrode material. Examples of suitable
dielectric materials comprise 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. or doped
versions of the same. For the purposes of illustration, dielectric
material, 806, will be rutile-phase TiO.sub.2 or tetragonal phase
ZrO.sub.2. As discussed previously, the TiO.sub.2 or the ZrO.sub.2
may be doped. Typically, the dielectric material is then subjected
to a PDA treatment. The second electrode material, 308, is then
formed above the dielectric material. For the purposes of
illustration, the second electrode material, 308, will be MoO.sub.2
in this example. As discussed previously, the second electrode
material may be doped with one or more dopants to alter the work
function and/or the resistivity of the second electrode material as
described previously. The capacitor stack is then subjected to a
PMA treatment. This completes the formation of the capacitor
stack.
[0089] In some embodiments, dopants including titanium oxide are
added to a second electrode material that includes molybdenum
oxide. In some embodiments, the dopants are added in a range
between about 1 atomic % and about 20 atomic %, such as between
about 5 atomic % and about 15 atomic %. Without being limited by
theory, it is believed that the titanium oxide serves two purposes
as a dopant within the molybdenum oxide. Firstly, the titanium
oxide may serve as an "oxygen sink" and scavenge oxygen from the
molybdenum oxide as it is converted from MoO.sub.3 to MoO.sub.2.
Secondly, the titanium oxide may exist in a rutile crystal
structure. Molybdenum oxide may also exist as a distorted rutile
crystal structure. Therefore, the titanium oxide may serve to
promote the crystallization of the molybdenum oxide during
subsequent anneal treatments. This may allow the molybdenum oxide
to be crystallized at lower temperatures that will not negatively
affect performance of the underlying dielectric materials.
[0090] In some embodiments, dopants including titanium nitride are
added to a second electrode material that includes molybdenum
oxide. In some embodiments, the dopants are added in a range
between about 1 atomic % and about 20 atomic %, such as between
about 5 atomic % and about 15 atomic %. Without being limited by
theory, it is believed that the titanium nitride serves two
purposes as a dopant within the molybdenum oxide. Firstly, the
titanium nitride may serve as an "oxygen sink" and scavenge oxygen
from the molybdenum oxide as it is converted from MoO.sub.3 to
MoO.sub.2. Secondly, the titanium nitride may exist in a cubic
crystal structure. Molybdenum oxide may exist as a distorted rutile
crystal structure. Molybdenum oxide in the form of MoO.sub.2 forms
readily on titanium nitride. Therefore, the titanium nitride may
serve to promote the crystallization of the molybdenum oxide during
subsequent anneal treatments. This may allow the molybdenum oxide
to be crystallized at lower temperatures that will not negatively
affect performance of the underlying dielectric materials.
[0091] FIG. 4 is used to illustrate another DRAM cell, 420,
manufactured using a first electrode structure and a doped second
electrode structure as discussed previously. In this example, the
second electrode structure includes multiple layers of materials.
The cell, 420, is illustrated schematically to include two
principle components, a cell capacitor, 400, and a cell transistor,
402. The cell transistor is usually constituted by a MOS transistor
having a gate, 418, source, 414, and drain, 416. 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 and an upper or plate electrode. 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.
[0092] As was described previously, the cell capacitor, 400,
comprises a first electrode material. First material layer, 404, is
formed on substrate, 401. The first electrode structure is
connected to the source or drain of the cell transistor, 402. For
illustrative purposes, the first electrode structure has been
connected to the source, 414, in this example. First material
layer, 404, comprises one of metals, conductive metal oxides,
conductive metal nitrides, conductive metal silicides, etc.
Optionally, the first material layer, 404, can be doped as
discussed below. The purpose of this layer is to provide high
conductivity to the first electrode structure. In some embodiments
the first material is a metal or a conductive metal nitride. As an
example, the first material may be titanium nitride. For the
purposes of another example, first electrode layer, 404, may be
crystalline MoO.sub.2 doped with one or more dopants in this
example as described previously. As used herein, the first
electrode structure materials will be considered to be crystallized
if they are .gtoreq.3% crystalline after the anneal as determined
by techniques such as x-ray diffraction (XRD). The doped first
electrode structure may contribute in lowering the leakage current
of the capacitor stack. As discussed previously, first electrode
structure, 404, may be subjected to an anneal in an inert or
reducing atmosphere before the formation of the dielectric material
to crystallize the MoO.sub.2 and to reduce any MoO.sub.2+x
compounds that may have formed during the formation of the first
electrode material.
[0093] Dielectric material, 408, is formed above the first
electrode structure. Examples of suitable dielectric materials
comprise 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. or doped
versions of the same. For the purposes of illustration, dielectric
material, 408, will be rutile-phase TiO.sub.2 or tetragonal phase
ZrO.sub.2. As discussed previously, the TiO.sub.2 or ZrO.sub.2 may
be doped. Typically, the dielectric material is then subjected to a
PDA treatment.
[0094] In the next step, the second electrode structure is
comprised of multiple layers of material. The third material layer,
410, is formed above dielectric material, 1008. The third material
layer comprises one of metals, conductive metal oxides, conductive
metal nitrides, conductive metal silicides, conductive metal
carbides, etc. For the purposes of illustration, third material
layer, 410, will be crystalline MoO.sub.2 doped with one or more
dopants in this example as described previously. The dopants may be
uniformly distributed throughout the third material layer or may be
distributed with a gradient in their concentration profile. Fourth
material layer, 412, is formed above third material layer, 410, and
comprises one of metals, conductive metal oxides, conductive metal
nitrides, conductive metal silicides, etc. Optionally, the fourth
material layer, 412, and be doped as discussed below. The purpose
of this layer is to provide high conductivity to the second
electrode structure. In some embodiments, the fourth material layer
is a metal or a conductive metal nitride. As an example, fourth
material layer, 412, comprises titanium nitride.
[0095] Dopants may be added to the second electrode structure
materials to alter properties such as the work function and the
resistivity. In some embodiments, the dopants are added in a range
between about 1 atomic % and about 20 atomic %, such as between
about 5 atomic % and about 15 atomic %. The dopants may be added to
the second electrode structure materials by introducing the dopant
species during the formation of the second electrode structure
materials. Typically, the second electrode structure materials are
formed using ALD or CVD technologies. In these cases, precursors
containing the dopant atoms may be introduced during the process
sequence of the ALD or CVD deposition step. The dopants may be
metals, metal oxides, metal nitrides, metal silicides, metal
carbides, non-metals, halogens, or combinations thereof (i.e.
metal-silicon-nitride, or metal-silicon-oxygen-nitride, etc). The
metal oxides, metal nitrides, metal silicides, metal carbides, and
combinations may be suitable as dopants because many of these
compounds are conductive, and as such, may advantageously alter the
work function and/or resistivity of the electrode material. The
dopants may be added individually or may be added in combination.
The dopants may be uniformly distributed throughout the second
electrode structure materials or may be distributed with a gradient
in their concentration profile. A second class of dopants may be
added to the second electrode material to alter the resistivity.
The dopants may be metals, metal oxides, metal nitrides, metal
silicides, metal carbides, non-metals, halogens, or combinations
thereof (i.e. metal-silicon-nitride, or
metal-silicon-oxygen-nitride, etc). The metal oxides, metal
nitrides, metal silicides, metal carbides, and combinations may be
suitable as dopants because many of these compounds are conductive,
and as such, may advantageously alter the work function and/or
resistivity of the electrode material. The dopants may be added
individually or may be added in combination. The dopants may be
uniformly distributed throughout the second electrode structure
materials or may be distributed with a gradient in their
concentration profile. The maximum doping concentration will vary
depending on the dopant material and subsequent anneal conditions.
Generally, the doping concentration is chosen such that it does not
prevent the second electrode structure materials from crystallizing
during the subsequent anneal step. As used herein, the second
electrode structure materials will be considered to be crystallized
if they are .gtoreq.30% crystalline after the anneal as determined
by techniques such as x-ray diffraction (XRD). Typically, the
capacitor stack would then be subjected to a PMA treatment. The
doped second electrode material may contribute in lowering the
leakage current of the capacitor stack.
[0096] In some embodiments, dopants including titanium oxide are
added to a second electrode material that includes molybdenum
oxide. In some embodiments, the dopants are added in a range
between about 1 atomic % and about 20 atomic %, such as between
about 5 atomic % and about 15 atomic %. Without being limited by
theory, it is believed that the titanium oxide serves two purposes
as a dopant within the molybdenum oxide. Firstly, the titanium
oxide may serve as an "oxygen sink" and scavenge oxygen from the
molybdenum oxide as it is converted from MoO.sub.3 to MoO.sub.2.
Secondly, the titanium oxide may exist in a rutile crystal
structure. Molybdenum oxide may also exist as a distorted rutile
crystal structure. Therefore, the titanium oxide may serve to
promote the crystallization of the molybdenum oxide during
subsequent anneal treatments. This may allow the molybdenum oxide
to be crystallized at lower temperatures that will not negatively
affect performance of the underlying dielectric materials.
[0097] In some embodiments, dopants including titanium nitride are
added to a second electrode material that includes molybdenum
oxide. In some embodiments, the dopants are added in a range
between about 1 atomic % and about 20 atomic %, such as between
about 5 atomic % and about 15 atomic %. Without being limited by
theory, it is believed that the titanium nitride serves two
purposes as a dopant within the molybdenum oxide. Firstly, the
titanium nitride may serve as an "oxygen sink" and scavenge oxygen
from the molybdenum oxide as it is converted from MoO.sub.3 to
MoO.sub.2. Secondly, the titanium nitride may exist in a cubic
crystal structure. Molybdenum oxide may exist as a distorted rutile
crystal structure. Molybdenum oxide in the form of MoO.sub.2 forms
readily on titanium nitride. Therefore, the titanium nitride may
serve to promote the crystallization of the molybdenum oxide during
subsequent anneal treatments. This may allow the molybdenum oxide
to be crystallized at lower temperatures that will not negatively
affect performance of the underlying dielectric materials.
[0098] 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.
* * * * *