U.S. patent application number 13/829856 was filed with the patent office on 2014-09-18 for silane and borane treatments for titanium carbide films.
The applicant listed for this patent is ASM IP HOLDING B.V.. Invention is credited to Tom E. Blomberg, Jerry Chen, Suvi Haukka, Dong Li, Vladimir Machkaoutsan, Jan Willem Maes, Brennan Milligan, Eric Shero.
Application Number | 20140273510 13/829856 |
Document ID | / |
Family ID | 51529008 |
Filed Date | 2014-09-18 |
United States Patent
Application |
20140273510 |
Kind Code |
A1 |
Chen; Jerry ; et
al. |
September 18, 2014 |
SILANE AND BORANE TREATMENTS FOR TITANIUM CARBIDE FILMS
Abstract
Methods of treating metal-containing thin films, such as films
comprising titanium carbide, with a silane/borane agent are
provided. In some embodiments a film comprising titanium carbide is
deposited on a substrate by an atomic layer deposition (ALD)
process. The process may include a plurality of deposition cycles
involving alternating and sequential pulses of a first source
chemical that comprises titanium and at least one halide ligand, a
second source chemical comprising metal and carbon, wherein the
metal and the carbon from the second source chemical are
incorporated into the thin film, and a third source chemical,
wherein the third source chemical is a silane or borane that at
least partially reduces oxidized portions of the titanium carbide
layer formed by the first and second source chemicals. In some
embodiments treatment forms a capping layer on the metal carbide
film.
Inventors: |
Chen; Jerry; (Chandler,
AZ) ; Machkaoutsan; Vladimir; (Wilrijk, BE) ;
Milligan; Brennan; (Gold Canyon, AZ) ; Maes; Jan
Willem; (Wilrijk, BE) ; Haukka; Suvi;
(Helsinki, FI) ; Shero; Eric; (Phoenix, AZ)
; Blomberg; Tom E.; (Vantaa, FI) ; Li; Dong;
(Phoenix, AZ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ASM IP HOLDING B.V. |
Almere |
|
NL |
|
|
Family ID: |
51529008 |
Appl. No.: |
13/829856 |
Filed: |
March 14, 2013 |
Current U.S.
Class: |
438/763 ;
438/785 |
Current CPC
Class: |
H01L 21/28568 20130101;
H01L 21/2807 20130101; H01L 21/02337 20130101; H01L 21/28556
20130101; H01L 21/02186 20130101; H01L 21/02321 20130101; H01L
21/28044 20130101; H01L 21/0228 20130101; H01L 21/28088
20130101 |
Class at
Publication: |
438/763 ;
438/785 |
International
Class: |
H01L 21/02 20060101
H01L021/02 |
Claims
1. A process for treating a film comprising titanium carbide, the
process comprising depositing a film comprising titanium carbide by
an atomic layer deposition process comprising a plurality of
deposition cycles, at least one cycle comprising: contacting a
substrate in a reaction space with alternating and sequential
pulses of a first source chemical that comprises a titanium halide
and a second source chemical that comprises a metal and an organic
ligand; and exposing the titanium carbide film to a silane/borane
agent, wherein after exposing the titanium carbide film comprises
less than about 20% titanium on an atomic basis.
2. The process of claim 1, wherein the film comprises at least
about 10% silicon on an atomic basis after exposing.
3. The process of claim 1, wherein the film comprises at least
about 25% silicon on an atomic basis after exposing.
4. The process of claim 1, wherein the film comprises more than
about 40% silicon, boron, and aluminum, combined, on an atomic
basis after exposing.
5. The process of claim 1, wherein the film forms part of a
dielectric/electrode stack having an equivalent oxide thickness of
less than about 1.3 nm.
6. The process of claim 1, wherein the film has a workfunction from
about 4.0 eV to about 4.4 eV.
7. The process of claim 1, wherein the silane/borane agent is
selected from the group consisting of monosilane, disilane,
trisilane, organosilanes, borane, diborane, and organoboranes.
8. The process of claim 1, wherein at least six deposition cycles
are completed prior to exposing the titanium carbide thin film to
the silane or borane agent.
9. The process of claim 1, wherein the film is exposed to the
silane or borane agent after each deposition cycle.
10. The process of claim 1, wherein the organic ligand is selected
from the group consisting of methyl and ethyl groups.
11. The process of claim 1, wherein the second source chemical is
trimethylaluminum (TMA) or triethylaluminum (TEA).
12. The process of claim 1, wherein the at least one deposition
cycle comprises: contacting the substrate with a titanium halide;
removing excess titanium halide from the reaction space; contacting
the substrate with an organometallic or metalorganic compound;
removing excess organometallic or metalorganic compound from the
reaction space; and the silane/borane agent is trisilane.
13. A method for depositing a metal carbide thin film on a
substrate in a reaction chamber, the method comprising a plurality
of deposition cycles, each cycle comprising contacting the
substrate with separate pulses of a first source chemical
comprising a titanium halide, a second source chemical comprising
carbon and aluminum, and a third source chemical comprising a
silane or a borane, and wherein the metal carbide film comprises
less than about 40% titanium on an atomic basis.
14. The method of claim 13, wherein the second source chemical is a
metalorganic compound.
15. The method of claim 13, wherein the third source chemical is
selected from the group consisting of monosilane, disilane,
trisilane, organosilanes, borane, diborane, and organoboranes.
16. The method of claim 13, wherein the second source chemical is
the next source chemical provided after the first source
chemical.
17. The method of claim 13, wherein the second source chemical is
the next source chemical provided after the third source
chemical.
18. A method of forming a silicon capping layer on a film
comprising titanium carbide, the method comprising: exposing the
film comprising titanium carbide to a silane or borane
compound.
19. The method of claim 18, wherein the titanium carbide layer is
exposed to the silane or borane compound for about 45 seconds to
about 180 seconds.
20. The method of claim 18, wherein the silicon capping layer is
less than about 3 nm thick.
21. The method of claim 18, wherein the film comprising titanium
carbide is directly over and contacting a dielectric layer.
22. The method of claim 18, additionally comprising depositing a
metal nitride layer directly over and contacting the titanium
carbide layer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to processes for
producing metal carbide thin films on a substrate by atomic layer
deposition. In some embodiments, titanium carbide films produced by
the atomic layer deposition (ALD) processes disclosed herein can be
used in metal gate and metal electrode applications in metal oxide
semiconductor field effect transistors (MOSFETs), such as n-channel
MOSFETs (NMOS).
[0003] 2. Description of the Related Art
[0004] Atomic layer deposition (ALD) is a generally self-limiting
process, whereby alternated pulses of reaction precursors saturate
a substrate surface and leave no more than about one monolayer of
material per pulse. The deposition conditions and precursors are
selected to provide self-saturating reactions, such that an
adsorbed layer in one pulse leaves a surface termination that is
non-reactive with the gas phase reactants of the same pulse. A
subsequent pulse of different reactants reacts with the previous
termination to enable continued deposition. Thus, each cycle of
alternated pulses leaves no more than about one molecular layer of
the desired material. The principles of ALD type processes have
been presented by T. Suntola, e.g. in the Handbook of Crystal
Growth 3, Thin Films and Epitaxy, Part B: Growth Mechanisms and
Dynamics, Chapter 14, Atomic Layer Epitaxy, pp. 601-663, Elsevier
Science B.V. 1994, the disclosure of which is incorporated herein
by reference.
[0005] In a typical ALD process for depositing thin films, one
deposition cycle comprises exposing the substrate to a first
precursor, removing unreacted first reactant and reaction
byproducts from the reaction chamber, exposing the substrate to a
second precursor, followed by a second removal step. Typically,
halide precursors, such as TiCl.sub.4 and HfCl.sub.4, are used as
precursors in ALD deposition because those precursors are
inexpensive and relatively stable, but at the same time reactive
towards different types of surface groups. H.sub.2O and NH.sub.3
are widely used for oxide and nitride deposition, respectively, as
second precursors.
[0006] ALD processes typically produce thin films that have lower
impurity content at the same deposition temperature than chemical
vapor deposition (CVD) processes. Despite the lower impurity levels
in ALD films, the impurity content in ALD films can still be a
problem. There are several possible reasons for the presence of
impurities in thin films deposited by ALD. In some cases, the
semiconductor process flow necessarily limits the maximum
deposition temperature such that that some residues are left in the
film. ALD films deposited from chloride or other halide-containing
precursors (e.g., WF.sub.6) at relatively low temperatures can
comprise relatively high levels of halide residues. Halide
impurities are present mainly at the interfaces, which can also
lead to problems. In some cases, like low temperature deposition of
transition metal nitrides and transition metal carbides from halide
containing precursors, the impurity contents can be above the
acceptable limit for some integrated circuit (IC) applications. In
another example, in some applications amorphous films are needed,
which limits the growth temperature.
[0007] In some ALD processes a deposited layer comprising Ti, Al,
and C can be undesirably oxidized by contaminants such as water and
air. In NMOS applications, oxidation of such a layer or thin film
may lead to a shift in the workfunction, for example, from N-type
to P-type.
SUMMARY OF THE INVENTION
[0008] According to some embodiments of the invention, an
organosilane, organoborane, silane, or borane (generally referred
to herein as a "silane/borane agent") is utilized in atomic layer
deposition (ALD) processes for depositing a boron- or
silicon-containing film comprising metal carbide from a
halide-containing precursor or in treating a deposited film that
comprises metal carbide. The silane/borane agent may be pulsed
during or after a deposition cycle, or it may be applied to a thin
film after some or all cycles have been completed. In some
embodiments, the silane/borane agent may serve to reduce oxidized
portions of a metal film. In some embodiments, the silane/borane
agent may form a barrier to at least partially prevent further
oxidation of the film itself or of films subsequently deposited
over the treated film. In some embodiments, the silane/borane agent
may help in gettering oxygen from deeper within a film, such as
oxygen coming from subsequent air exposure.
[0009] In some embodiments, the silane/borane treatment may form a
capping layer comprising silicon or boron. In some embodiments the
capping layer may comprise a portion of the metal carbide layer
that comprises silicon or boron. In some embodiments the capping
layer is formed directly on the metal carbide layer. In some
embodiments the capping layer comprises a portion of the metal
carbide film comprising silicon or boron as well as a layer
comprising silicon or boron formed on the metal carbide layer.
[0010] In some cases, the barrier effect of the silane/borane agent
treatment may also prevent or limit oxidation of one or more layers
deposited after the silane/borane treatment of the metal carbide
film. For example, the use of a silane/borane agent in the
formation or treatment of a metal carbide film, such as a titanium
carbide film, may limit oxidation of a second film deposited over
the titanium carbide film, such as a nitride film (for example TiN)
even if the second film is not itself treated with a silane/borane
agent. Additional subsequently deposited films may also be
protected from oxidation by the silane/borane agent treatment of
the metal carbide layer.
[0011] In some embodiments, however, additional films deposited
after the metal carbide, such as a titanium nitride film, a hafnium
oxide film, a silicon or silicon oxide film, or a tungsten film,
are themselves treated with a silane/borane agent to achieve at
least some of the advantages enjoyed by the treated metal carbide
films.
[0012] The duration of the silane/borane agent exposure can be
controlled to achieve a desired result. For example, the duration
of exposure can be based on a desired level of interaction with the
metal film and the desired depth of diffusion or penetration into
the film. In some embodiments the duration of the exposure is
controlled to form a capping layer of a desired thickness and/or
composition.
[0013] In some embodiments, the silane/borane is selected from the
group consisting of organosilanes and organoboranes, monosilane,
disilane, trisilane, borane, diborane, and triborane. The
silane/borane agent may be provided in each ALD cycle, at intervals
during the deposition process, or after the completion of some or
all of the cycles. In some embodiments, the silane/borane agent may
be provided to the substrate in vapor form. In some embodiments the
silane/borane agent, such as trisilane, may be applied to the
substrate in liquid form.
[0014] In some embodiments, ALD processes for forming a
titanium-carbide thin film are disclosed. The processes may
comprise contacting a substrate in a reaction space with
alternating and sequential pulses of a titanium source chemical
that comprises at least one halide ligand, a second source chemical
comprising a metal and carbon and a third source chemical, wherein
the third source chemical is a silane/borane. As discussed in more
detail below, the third source chemical may be applied as a part of
each deposition cycle, as a part of only some cycles, or after all
the cycles have been completed. The second source chemical may
comprise an organic ligand, and in some embodiments may be TMA
(trimethylaluminum) or TEA (triethylaluminum). In some embodiments,
the second source chemical is dimethylaluminumhydride DMAH or
tris(tertbutyl)aluminum TTBA.
[0015] In some embodiments, ALD processes for forming a titanium
carbide film are disclosed, in which alternating and
self-saturating pulses of reactants are provided in a plurality of
deposition cycles. Each cycle preferably comprises contacting a
substrate in a reaction space with alternating and sequential
pulses of a titanium source chemical, preferably a titanium halide
compound, a carbon source chemical, and a silane or borane source
chemical. The silane or borane source chemical can be selected from
monosilane, disilane, trisilane, borane, and diborane, organosilane
and organoborane, and in one embodiment is trisilane.
[0016] In yet another aspect of the invention, a semiconductor
device structure is disclosed. The structure comprises a substrate
and a thin film layer overlying the substrate, wherein the thin
film layer is formed by ALD by contacting the substrate with
alternating and sequential pulses of a metal source chemical, a
carbon source chemical, and a silane/borane agent.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The invention will be better understood from the Detailed
Description of the Preferred Embodiments and from the appended
drawings, which are meant to illustrate and not to limit the
invention, and wherein:
[0018] FIG. 1 is a flow chart generally illustrating a method of
forming a binary compound by ALD, in which supply of a
silane/borane agent follows removal of excess second reactant and
by-products, in accordance with some embodiments of the
invention;
[0019] FIG. 2 is a schematic cross-sectional side view of a
electrode structure, comprising a layer of a conductive metal
carbide, according to some embodiments of the invention; and
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0020] The present disclosure provides atomic layer deposition
(ALD) methods for forming metal carbide thin films, such as
titanium carbide thin films. Although described primarily in terms
of titanium carbide thin films, other types of thin films may be
deposited and/or treated with the disclosed methods, such as
niobium carbide films, as discussed in more detail below.
[0021] The ALD methods may comprise exposing the films to silane or
borane to reduce or substantially prevent oxidation of the titanium
carbide film and the accompanying buildup of oxygen at the
interface of the titanium carbide film and an overlying layer as
well as diffusion of possible oxygen beyond the interface between a
titanium carbide film and an underlying layer. As mentioned above,
such a buildup of oxidation can cause a shift in the workfunction
of the thin film. In some embodiments, a silane or borane treatment
can be used to reduce the resistivity of a thin titanium carbide
film. The silane or borane may be provided during each titanium
carbide deposition cycle, after a certain number of titanium
carbide deposition cycles, or after all the titanium carbide
deposition cycles have been completed. In some preferred
embodiments, the silane or borane agent is a borane or an
organoborane, such as diborane, or a silane or organosilate, such
as silane, disilane, or trisilane.
DEFINITIONS
[0022] As used in this disclosure, the term "ALD process" is used
in accordance with its ordinary meaning in this field and includes
a process for producing thin films over a substrate in which a thin
film is formed molecular layer by molecular layer due to
self-saturating chemical reactions. The general principles of ALD
are disclosed, for example, in U.S. Pat. Nos. 4,058,430 and
5,711,811, the disclosures of which are incorporated herein by
reference. In an ALD process, gaseous reactants, i.e., precursors,
are conducted into a reaction chamber of an ALD type reactor where
they contact a substrate located in the chamber to provide a
surface reaction. The pressure and the temperature of the reaction
chamber are adjusted to a range where physisorption (i.e. physical
adsorption or condensation of gases) and thermal decomposition of
the precursors are avoided. Consequently, only up to about one
monolayer (i.e. an atomic layer or a molecular layer) of material
is deposited at a time during each pulsing cycle. The actual growth
rate of the thin film, which is typically presented as
.ANG./pulsing cycle, depends, for example, on the number of
available reactive surface sites or active sites on the surface and
bulkiness of the chemisorbing molecules. Gas phase reactions
between precursors and any undesired reactions of by-products are
inhibited because precursor pulses are separated from each other by
time and the reaction chamber is purged with an inactive gas (e.g.
nitrogen or argon) and/or evacuated using, e.g., a pump between
precursor pulses to remove surplus gaseous reactants and reaction
by-products from the chamber.
[0023] As used in this disclosure, the term "reaction space" is
used in accordance with its ordinary meaning in this field and
includes a reactor or reaction chamber, or an arbitrarily defined
volume therein, in which conditions can be adjusted to effect thin
film growth by ALD. Typically the reaction space includes surfaces
subject to all reaction gas pulses from which gases or particles
can flow to the substrate, by entrained flow or diffusion, during
normal operation. The reaction space can be, for example, in a
single-wafer ALD reactor or a batch ALD reactor, where deposition
on multiple substrates takes place at the same time.
[0024] As used in this disclosure, the term "adsorption" is used in
accordance with its ordinary meaning in this field and includes a
chemical attachment of atoms or molecules on a surface.
[0025] As used in this disclosure, the term "soak" describes
exposing a thin film, such as a titanium carbide film, to a
chemical such as a silane/borane agent for a period of about 10
seconds to about 600 seconds, preferably from about 30 seconds to
about 300 seconds and more preferably from about 45 seconds to
about 180 seconds. In some cases, the duration of a soak is longer
than the duration of a pulse of titanium or carbon reactants in an
ALD cycle. The duration of a soak may be adjusted to obtain a
desired amount of silicon in a metal carbide film. For example the
duration of the soak can be adjusted to determine a penetration
depth or the extent of diffusion in the metal carbide film. In some
embodiments the Si does not necessarily penetrate into the film, as
its presence on the surface of the film may serve as an oxygen or
oxidation barrier (or nitrogen barrier, for example where a
subsequent layer such as a TiN is deposited on the treated
film).
[0026] As used in this disclosure, the term "thin film" is used in
accordance with its ordinary meaning in this field and includes a
film that is grown from elements or compounds that are transported
as separate ions, atoms or molecules via vacuum, gaseous phase or
liquid phase from the source to the substrate. The thickness of the
film depends upon the application and may vary in a wide range,
preferably from one atomic layer to 1,000 nm or more. In some
embodiments, the thin film is less than about 20 nm in thickness,
even more preferably less than about 10 nm and most preferably less
than about 5 nm or less than about 3 nm.
[0027] Subscripts "x" and "y" are used to designate species that
are not necessarily stoichiometric, having a wide range of phases
with varying metal/oxygen, metal/carbon, metal/nitrogen, or
metal/carbon/nitrogen ratios.
ALD Methods
[0028] The methods presented herein allow deposition of conformal
metal carbide thin films on substrate surfaces. In some
embodiments, thin films are deposited from halogen-containing
chemicals. Geometrically challenging applications are also possible
due to the self-limited nature of the surface reactions in ALD
processes.
[0029] According to some embodiments, an ALD type process is used
to form titanium carbide thin films on substrates, such as
integrated circuit workpieces. The surfaces on which the thin
titanium carbide (TiC) films are deposited can take a variety of
forms. Examples include, but are not limited to, silicon, silicon
oxide (SiO.sub.2), coated silicon, dielectric materials, low-k
materials, metals--such as copper and aluminum--metal alloys, metal
oxides and various nitrides, such as transition metal nitrides and
silicon nitride or a combination of said materials. In some
embodiments, the substrate comprises titanium nitride. In some
embodiments, the substrate comprises hafnium oxide.
[0030] In a some embodiments, a substrate or workpiece is placed in
a reaction chamber and subjected to alternately repeated surface
reactions. In particular, thin films are formed by repetition of an
ALD cycle. Each ALD cycle is typically self-limiting. In the case
of compound metallic thin film deposition, at least two different
source chemicals are alternatively employed. One reactant will form
no more than about one monolayer on the substrate surface and
includes a metal species desired in the layer being deposited. This
reactant, also referred to herein as "the metal reactant," is
preferably a titanium halide, such as TiCl.sub.4, or a niobium
halide, such as NbCl.sub.5, and thus the deposited monolayer is
terminated with halogen ligands.
[0031] A second reactant preferably contributes carbon to the
growing film. In some embodiments, the second reactant comprises a
metal and carbon, such as TMA or TEA. In some embodiments, the
second reactant is a metal-containing source chemical comprising at
least one ligand, such as a metalorganic compound. Further, in some
embodiments the second reactant can also leave some amount of metal
in the film being deposited. For example, in the case of TMA or
TEA, some amount of aluminum may be left in the film, depending on
the particular reaction conditions. In some embodiments, the
formation of an aluminum carbide in the form of Al.sub.xC.sub.y may
also provide protection against oxidation.
[0032] In some embodiments according to the present disclosure, a
third reactant is provided every cycle, after a certain number of
cycles, or after deposition of the metal carbide film is complete.
The third reactant may be a silicon compound, or a boron compound,
preferably one that is a strong reducer. In some embodiments the
third reactant comprises a silane/borane agent. The silane/borane
agent is more reactive to oxygen than is the metal of the metal
carbide film, for example titanium and/or niobium, and thus is
capable of reducing the amount of metal oxide in the film. In some
cases, little or no oxygen is actually removed from the thin film;
however, the silane/borane agent acts to reduce metal oxide, such
as titanium oxide by breaking the bonds between titanium and oxygen
to return the titanium to its pure titanium carbide form. In such
cases, although, the oxygen has not actually been removed from the
film, it is bound up by the silane/borane agent so as to not impede
the workfunction of the thin film. Accordingly, it could also be
said that application of a silane/borane agent increases the amount
of TiC compared to the amount of TiOC in the film. Moreover, in
some embodiments the third reactant also provides a species desired
in the thin film, such as silicon, boron, or carbon. However, it
should be mentioned that in some embodiments, there will be little
or no oxygen for the silane/borane agent to bond with during the
deposition process. In such cases, the silicon or boron deposited
with the TiC thin film may act as a barrier to oxygen if and when
the TiC film is exposed to oxygen, such as when a workpiece is
moved from one chamber to another. For example, treatment of a
titanium carbide layer during deposition may reduce or prevent
oxidation of the titanium carbide layer when it is moved to another
reactor for further processing, such as deposition of an overlying
titanium nitride layer.
[0033] The silane/borane agent may be selected from the group
consisting of monosilane, disilane, trisilane, organosilanes,
borane, diborane, organoboranes, or any other suitable material
that readily reacts with oxygen to reduce titanium, niobium or
other metal in the metal carbide. The silane/borane agent may be
supplied in vapor or liquid form, and may be applied as a
relatively short pulse every cycle or intermittently in the
deposition process or as a relatively longer soak to a partially or
completely formed titanium carbide layer.
[0034] The silane/borane agent may be provided in each ALD cycle,
at intervals during the deposition process, or after the deposition
process has been completed. For example, in some embodiments the
silane/borane agent is provided every one to four ALD cycles. In
some embodiments, at the time the silane/borane agent is provided,
the film grown in the most recent ALD cycles is preferably thin
enough that the silane/borane agent can penetrate the film. In some
embodiments, such as situations where more than one deposition
cycle has been completed prior to exposure to the silane/borane
agent, the amount of silane/borane penetration in the films can be
controlled by the quantity or concentration of the agent used or
the duration of the exposure.
[0035] The silane/borane agent may be provided as a part of one or
more cycles or may be applied after one or more cycles have been
completed. Thus, in some embodiments, the deposition of a metal
carbide film, such as TiC, is considered to be a cycle in an ALD
process independent of the application of a silane/borane agent. In
such cases, the cycle is repeated as many times as desired, and the
silane/borane treatment is applied after some or all of the cycles.
However, in some embodiments, the silane/borane agent is applied
during one or more cycles (as a part of an ALD cycle) as well as
after one or more cycles (separate from an ALD cycle).
[0036] In one phase of an ALD cycle ("the metal phase", for example
"the titanium phase" or the "first phase"), the reactant or source
chemical comprising titanium (or other metal such as niobium) is
supplied to the reaction chamber and chemisorbs to the substrate
surface. The reactant supplied in this phase is selected such that,
under the preferred conditions, the amount of reactant that can be
bound to the surface is determined by the number of available
binding sites and by the physical size of the chemisorbed species
(including ligands). The chemisorbed layer left by a pulse of the
titanium reactant is self-terminated with a surface that is
non-reactive with the remaining chemistry of that pulse. This
phenomenon is referred to herein as "self-saturation." One of skill
in the art will recognize that the self-limiting nature of this
phase makes the entire ALD cycle self-limiting. Excess reactant and
reactant byproducts (if any) are removed from the reaction space,
for example by purging with an inert gas and/or evacuation.
[0037] Maximum step coverage and conformality on the workpiece
surface is obtained when no more than about a single molecular
layer of metal source chemical molecules is chemisorbed in each
self-limiting pulse. Due to the size of the chemisorbed species and
the number of reactive sites, somewhat less than a monolayer may be
deposited in each pulse of metal reactant. However, the use of some
reactants, such as TEA or TMA, may result in more than a monolayer
because they may at least partially self-decompose at the
deposition temperature. The degree of self-decomposition can be a
function of pulse time.
[0038] In the next phase of the cycle, a pulse of a second source
chemical is provided that reacts with the molecules left on the
substrate surface by the preceding pulse. In some embodiments the
source chemical preferably comprises carbon that is to be
incorporated in the thin film. The carbon is incorporated into the
thin film by the interaction of the source chemical with the
monolayer left by the metal reactant. This phase is referred to
herein as "the second phase" or the "carbon-contributing phase." In
some embodiments, the second source chemical is a carbon containing
compound and its reaction with the chemisorbed metal species
produces a metal carbide layer on the substrate. In some
embodiments the second source chemical also comprises a second
metal, such as aluminum, and the second metal is incorporated into
the growing film along with the carbon. In some embodiments the
species-contributing source chemical comprises metal and carbon and
may be, for example, TMA or TEA.
[0039] Excess second source chemical and reaction byproducts, if
any, are removed from the reaction space by purging and/or
evacuation.
[0040] In some embodiments, a third phase of the ALD cycle
comprises providing the silane/borane agent. The silane/borane
agent may comprise a species that may be incorporated into the thin
film, such as boron or silicon. This is referred to as the "third
phase" or the "oxygen isolation phase."
[0041] Although referred to as the "first phase," the "second
phase" and the "third phase," these labels are for convenience and
do not indicate the actual order of the phases in each ALD cycle.
Thus, the initial ALD cycle may be started with any of the three
phases described above. However, one of skill in the art will
recognize that if the initial ALD cycle does not begin with the
metal reactant phase, at least two ALD cycles will typically need
to be completed to deposit about a monolayer of the desired metal
carbide thin film.
[0042] In addition, the order of the phases may be changed. That
is, in some embodiments the silane/borane agent may be the next
reactant provided after the second reactant, while in other
embodiments the silane/borane agent may be the next reactant
provided after the first metal source reactant. And in some
embodiments, the silane/borane agent may be supplied after only
some cycles or after all cycles have been completed. For example,
in some embodiments the third phase (provision of the silane/borane
agent) may immediately follow the first phase (provision of the
reactant comprising a metal species), which in turn is followed by
the carbon-contributing phase. And in some embodiments, the third
phase may be supplied as a vapor "soak" after the thin film has
been completely formed. That is, the deposited film is exposed to a
silane or a borane in vapor form for a period of time. A phase is
generally considered to immediately follow another phase if only a
purge or other reactant removal step intervenes.
[0043] In some embodiments the silane/borane agent is not provided
in every ALD cycle. Rather, a partially or completely deposited
titanium carbide film may be treated with a silane/borane agent.
This may be the case, for example, where a first film has been
formed using TiCl.sub.4 and TEA but the resulting TiAlC film has
been oxidized by water, air, or some other contaminant source to
form a layer that is essentially TiAlOC. A silane/borane agent can
be applied to the first film which may reduce the TiAlOC layer back
to essentially TiAlC with only the minor presence of
impurities.
[0044] In one embodiment, an ALD cycle comprises: [0045] 1.
providing a titanium halide to the reaction space; [0046] 2.
substantially purging and/or evacuation of excess titanium halide
and reaction byproducts; [0047] 3. providing a carbon-contributing
reactant to the reaction space, such TEA or TMA; [0048] 4.
substantially purging and/or evacuation of excess second reactant
and reaction byproducts; and [0049] 5. providing a silane/borane
agent to the reaction space.
[0050] Step 5 can be included in each ALD cycle, or steps 1-4 can
be repeated several times before step 5 is introduced. In some
embodiments steps 1-4 are repeated up to 10 times before step 5 is
included. In other embodiments steps 1-4 are repeated up to 100 or
even 1000 or more times before step 5 is included. In some
embodiments, a complete film of desired thickness is deposited
prior to step 5.
[0051] With reference to FIG. 1, in an embodiment of the invention,
after initial surface termination, if necessary, a first reactant
or source chemical pulse is supplied 102 to the substrate or
workpiece. In the illustrated embodiment, the first reactant is a
metal halide, and the thin film being formed comprises a metal
carbide. In accordance with a preferred embodiment, the first
reactant pulse comprises a carrier gas flow and a volatile titanium
halide species that is reactive with the workpiece surfaces of
interest. Accordingly, the halogen-containing titanium species
adsorbs upon the workpiece surfaces. The first reactant pulse
self-saturates the workpiece surfaces such that any excess
constituents of the first reactant pulse do not further react with
the monolayer formed by this process. Self-saturation results due
to halide tails terminating the monolayer, protecting the layer
from further reaction.
[0052] The first reactant is then removed 104 from the reaction
space. Step 104 may entail merely stopping the flow of the first
reactant or chemistry while continuing to flow a carrier gas for a
sufficient time to diffuse or purge excess reactants and reactant
by-products from the reaction space. Preferably the removal 104
comprises continuing to flow purge gas for between about 0.1
seconds and 20 seconds after stopping the flow of the first
reactant pulse. Inter-pulse purging is described in co-pending U.S.
Pat. No. 6,511,539, entitled "IMPROVED APPARATUS AND METHOD FOR
GROWTH OF A THIN FILM," the disclosure of which is incorporated
herein by reference. In other arrangements, the chamber may be
pumped down between alternating chemistries. See, for example, PCT
publication number WO 96/17107, published Jun. 6, 1996, entitled
"METHOD AND APPARATUS FOR GROWING THIN FILMS," the disclosure of
which is incorporated herein by reference. Together, the adsorption
102 and reactant removal 104 represent a first phase 105 in an ALD
cycle. The first phase in the illustrated ALD cycle is thus the
metal phase.
[0053] With continued reference to FIG. 1, a second reactant or
source chemical pulse is then supplied 106 to the workpiece. The
second chemical reacts with the monolayer left by the first
reactant. In the illustrated embodiment, this second reactant pulse
106 comprises supplying a carrier gas with the second source gas to
the workpiece. In particular, where the first reactant comprises a
titanium halide, the second reactant, such as TMA or TEA, comprises
carbon and a second, different metal. In the case of TEA or TMA the
second reactant leaves no more than about a monolayer of TiAlC. The
second reactant preferably removes at least some halide ligands
from the adsorbed first reactant. The second reactant pulse 106
also leaves a surface termination that operates to limit the
deposition in a saturative reaction phase.
[0054] After a time period sufficient to completely saturate and
react the monolayer with the second reactant pulse 106, any excess
second reactant is removed 108 from the workpiece. As with the
removal 104 of the first reactant, this step 108 may comprise
stopping the flow of the second chemistry and continuing to flow
carrier gas for a time period sufficient for excess reactants and
volatile reaction by-products from the second reactant pulse to
diffuse out of and be purged from the reaction space. Together, the
second reactant pulse 106 and removal 108 represent a second phase
109 in the illustrated process, and can also be considered a carbon
and metal species-contributing phase.
[0055] When the excess reactants of the second reactant pulse have
been removed 108 from the chamber, a third reactant or source
chemical pulse may be supplied to the workpiece 110. The third
reactant can be a silane/borane agent capable of removing halides
and/or reacting with oxygen in the growing film. Examples of
suitable silanes and boranes include monosilane, disilane,
trisilane, borane, and diborane. The silane/borane agent may be
provided with an inert carrier gas. Temperature and pressure
conditions can be adjusted to control the level of diffusion of the
silane/borane agent through the monolayer.
[0056] After a time period sufficient to achieve a desired level of
saturation of the third reactant in the monolayer, excess unreacted
silane/borane agent and any reaction by-products (which may also be
volatile) are removed 112 from the reaction space, for example by a
purge gas pulse. The removal can be as described for step 104.
Together, the silane/borane agent pulse 110 and removal 112
represent a third phase 113 of the illustrated ALD process, which
can also be referred to as the oxygen isolation phase.
[0057] In some embodiments, supply of silane/borane agent
immediately follows the step of removing excess first reactant and
by-products. After a time period sufficient to react the monolayer
with the silane/borane agent, excess unreacted silane/borane agent
and reaction by-products are removed from the reaction space,
possibly by a purge gas pulse. The removal step is followed by
supply of the second reactant pulse.
[0058] In some embodiments of the disclosure (not shown), the steps
of supplying the silane/borane agent and removing any excess
silane/borane agent and by-products precede the step of supplying
the first reactant. In some embodiments, the silane/borane agent is
not provided in every cycle or may be provided after all the cycles
are complete.
[0059] In some embodiments, the step of supplying a silane/borane
agent take the form of a soak occurring after some or all of the
titanium carbide deposition cycles have been completed. In some
cases, a soak of trisilane occurring after deposition of a TiC film
is completed has been found to achieve suitable results.
[0060] In one embodiment, a process for forming a titanium carbide
film comprises: [0061] 1. providing a titanium halide, such as a
titanium chloride, to the reaction space; [0062] 2. substantially
purging and/or evacuation of excess titanium halide and reaction
byproducts; [0063] 3. providing a second carbon and
aluminum-contributing reactant, such as TEA or TMA, to the reaction
space; [0064] 4. substantially purging and/or evacuation of excess
second reactant and reaction byproducts; [0065] 5. repeating steps
1 through 4 for either a desired number of cycles or until a film
of a desired thickness has been achieved; and [0066] 6. soaking the
product of step 5 with a silane/borane agent
[0067] In some embodiments the soak of Step 6 can be configured to
achieve a particular level of interaction between any oxygen
present in the film and the silane/borane agent. In some
embodiments the soak of Step 6 can be configured to provide a
desired amount of silicon or boron in the film to a particular
depth. For example, the soak may last long enough to allow silicon
or boron to substantially diffuse throughout the film or the soak's
duration may be kept shorter so as to reach only a partial depth in
the film. The duration of the soak may be from about 5 seconds to
about 600 seconds, preferably from about 10 seconds to about 180
seconds, more preferably from about 20 seconds to about 120 seconds
and in some embodiments from about 30 seconds to about 60 seconds.
In some cases, such as batch processes, the soaking time might be
even longer. In some such embodiments, the soak is performed for
about 30 seconds to about 600 seconds, preferably from about 45
seconds to about 180 seconds, more preferably from about 60 seconds
to about 120 seconds.
[0068] In some embodiments, a soak may serve to "cap" a thin film
with an oxygen barrier by providing silicon or boron in a portion
of the film or on the film itself. In some embodiments, a deposited
or partially deposited metal carbide layer is soaked in a
silane/borane agent, such as disilane or trisilane, to form a thin
"capping" layer having a thickness below about 3 nm, more
preferably below about 2 nm and most preferably below about 1 nm.
Formation of a capping layer in the initial phase of the soak may
stop the diffusion of silicon or boron into the film while still
having a beneficial effect on the surface of the film.
[0069] According to some embodiments, the capping layer is a
separate layer comprising silicon or boron and formed directly on
the thin film. In some embodiments, the capping layer may also or
alternatively comprise a portion of the metal carbide layer, or
whatever layer it is applied to, where that portion comprises
silicon or boron from the treatment with the silane or borane
agent. The nature of the capping layer may depend, for example, on
the treatment conditions and/or the silane/borane agent that is
used. Where the capping layer comprises a portion of the underlying
metal layer, such as a metal carbide layer, there may be a gradient
within the underlying layer with a greater concentration of the
silicon or boron toward the top of the layer and a decreasing
concentration at increased depths from the top of the layer. The
gradient--both the depth to which the silane/borane agent extends
as well as the concentration at any given depth--may depend, in
part on the treatment conditions (duration, temperature, pressure,
etc.) and the particular silane/borane agent used. According to
some embodiments, the silane/borane agent may at least partially
react with the underlying layer. In some cases, the capping layer
may comprise a layer comprising silicon or boron formed directly on
the underlying film as well as a portion of the film in which
silicon or boron is present. In some embodiments the capping layer
is a silicon or boron layer formed directly over and contacting a
metal carbide layer, such as a TiC layer.
[0070] According to some embodiments, the reaction temperature may
be from about 300.degree. C. to about 500.degree. C., preferably
from about 325.degree. C. to about 450.degree. C., and more
preferably from about 350.degree. C. to about 450.degree. C.
[0071] The foregoing embodiments will be discussed in the context
of specific thin film chemistries.
Deposition of Carbon-Containing Films
[0072] Carbon containing metal films or metal carbides have varying
applications, such as gate electrodes, electrodes in capacitors and
barrier layers in damascene and dual damascene structures.
[0073] In some embodiments, a general pulsing sequence for
carbon-containing metal or metal carbide thin film deposition
is:
(M.sup.1X.sub.y+purge+M.sup.2R.sub.3+purge+silane/borane
agent+purge).times.m.sub.1
or
(M.sup.1X.sub.y+purge+silane/borane
agent+purge+M.sup.2R.sub.3+purge).times.m.sub.1, [0074] wherein
m.sub.1 is the number of total cycles. M.sup.1 is a metal atom,
preferably selected from the group consisting of Ti, Zr, Hf, V, Nb,
Ta, Cr, Mo, W.
[0075] M.sup.2 is a metal atom, preferably selected from the group
consisting of B, Al, In, Bi, Sn, Zn, Pb, Sb and Ga. R is a ligand
for M.sup.2 and can be any ligand, preferably a metalorganic
ligand, more preferably an organometallic ligand, most preferably
an alkane ligand, such as ethyl ligand.
[0076] X.sub.y is one or more ligands for M.sup.1. Each X may be a
halogen ligand selected from the group consisting of I, Br, Cl and
F. However, in some embodiments at least one X can be a
metalorganic ligand, such as a cyclopentadienyl (for example,
cyclopentadienyl, methylcyclopentadienyl,
pentamethylcyclopentadienyl, ethylcyclopentadienyl,
isopropylcyclopentadienyl, tertbutylcyclopentadienyl, and indenyl),
alkyl (for example, methyl, ethyl, propyl, and butyl), carbonyl,
cyclo-octadiene, benzene or hydrogen ligand. In other embodiments
X.sub.y may comprise mixtures thereof. However, at least one of the
X.sub.y ligands is preferably a halogen. As an example,
bis(cyclopentadienyl)hafnium dichloride or
bis(cyclopentadienyl)tantalum(V) trichloride, can be used as a
metal precursor in some embodiments. In some embodiments no X is
oxygen or nitrogen.
[0077] The silane/borane agent may be selected from the group
consisting of monosilane, disilane, trisilane, borane, and
diborane. In some embodiments, the silane/borane agent is a
disilane or a trisilane that is applied during or after each layer
is deposited, after only some layers are deposited, or after all
the layers have been deposited. The silane/borane agent can be
applied in a pulse or as a soak and as a liquid or a vapor.
[0078] In preferred embodiments, M.sup.2 is a metal, preferably
aluminum, and R is a carbon-containing ligand. M.sup.2R.sub.3
preferably has at least one metal-to-carbon bond. In some
embodiments, M.sup.2R.sub.3 may be considered a carbon source
chemical. In some embodiments, M.sup.2R.sub.3 is selected from the
group consisting of TMA and TEA. In some embodiments M.sup.2R.sub.3
is DMAH. In some embodiments M.sup.2R.sub.3 is TTBA.
[0079] One benefit of the ALD processes of some embodiments is that
the growth rate is extremely high for an ALD process. For example,
the growth rate for TaC formation can be over 2 .ANG./cycle.
Further, annealing can be performed after the metal carbide
deposition for enhancing the properties of the film. Suitable
atmospheres, such as N.sub.2 or forming gas (N.sub.2/H.sub.2), may
be used during annealing.
[0080] Exemplary pulsing sequences for TiC film formation
include:
(TiCl.sub.4+purge+trimethylaluminum (TMA) or triethylaluminum
(TEA)+purge+silane/borane agent+purge)].times.m.sub.2
and
(TiCl.sub.4+purge+silane/borane agent+purge+TMA or
TEA+purge)].times.m.sub.2, [0081] wherein m.sub.2 is the number of
total cycles and the silane/borane agent is selected from the group
consisting of monosilane, disilane, trisilane, borane, and
diborane.
[0082] Films deposited using the above exemplary pulsing sequence
contained, based on an atomic basis, about 17-20% Ti, about 17-27%
Al, about 16-42% Si, and about 21-39% C. These values were
determined using Rutherford backscattering spectrometry, or
RBS.
[0083] In other embodiments, a silane/borane agent is not utilized
every cycle but only in some of the cycles. In this situation, a
general pulsing sequence for carbon-containing metal thin film
deposition can be:
[n.sub.3.times.(M.sup.1X.sub.y+purge+M.sup.2R.sub.3+purge)+m.sub.3.times-
.(silane/borane agent+purge)].times.k.sub.3,
[0084] wherein n.sub.3 is the number of carbide cycles in one total
cycle, m.sub.3 is the number of cycles in which a silane/borane
agent is used in one total cycle, and k.sub.3 is the number of
total cycles. M.sup.1 is preferably Ti but may be a metal atom
selected from the group consisting of Zr, Hf, V, Nb, Ta, Cr, Mo,
and W. M.sup.2 is preferably Al but may be a metal atom selected
from the group consisting of B, Al, In, Sn, Bi, Zn, Pb, Sb and Ga.
R is a ligand for M.sup.2 and can be any ligand.
[0085] X.sub.y is one or more ligands for M.sup.1. Each X is
preferably a halogen ligand selected from the group consisting of
I, Br, Cl and F. However, in some embodiments at least one X can be
a metalorganic ligand, such as a cyclopentadienyl (for example,
cyclopentadienyl, methylcyclopentadienyl,
pentamethylcyclopentadienyl, ethylcyclopentadienyl,
isopropylcyclopentadienyl, tertbutylcyclopentadienyl, and indenyl),
alkyl (for example, methyl, ethyl, propyl, and butyl), carbonyl,
cyclo-octadiene, benzene or hydrogen ligand. In other embodiments
X.sub.y may comprise mixtures thereof. However, at least one of the
X.sub.y ligands is preferably a halogen. As an example,
bis(cyclopentadienyl)hafnium dichloride or
bis(cyclopentadienyl)tantalum(V) trichloride, can be used as a
metal precursor in some embodiments. In some embodiments no X
comprises nitrogen or oxygen.
[0086] According to some embodiments, the reaction temperature may
be from about 300.degree. C. to about 500.degree. C., preferably
from about 325.degree. C. to about 450.degree. C., and more
preferably from about 350.degree. C. to about 450.degree. C.
[0087] The exact composition of a thin film produced using the
methods and materials disclosed herein may vary. Titanium carbide
films fabricated according to the present disclosure may contain a
number of differing elemental components including, but not limited
to titanium, aluminum, carbon, silicon and/or boron depending in
part on the type of silane/borane agent used.
[0088] In some embodiments, the atomic percentage of titanium, or
other suitable metal, could be from about 10-30%, about 10-25%, or
even about 15-20%. In some embodiments, the atomic percentage of
aluminum could be greater than about 15%, greater than about 20%,
or even greater than about 25%. In some embodiments, the atomic
percentage of silicon or boron could be greater than about 10%,
greater than about 25%, or greater than about 35%. In some
embodiments, the atomic percentage of carbon could be less than
about 40%, less than about 30%, or less than about 25%.
[0089] In some embodiments, a metal carbide film comprise, on an
atomic basis, about 10-30% titanium, greater than about 15%
aluminum, greater than about 10% silicon or boron, and less than
about 40% carbon. In some embodiments, a metal carbide film
comprise, on an atomic basis, about 10-25% titanium, greater than
about 20% aluminum, greater than about 25% silicon or boron, and
less than about 30% carbon. In some embodiments, a metal carbide
film comprise, on an atomic basis, about 15-20% titanium, greater
than about 25% aluminum, greater than about 35% silicon or boron,
and less than about 25% carbon.
[0090] In some embodiments, the atomic percentage of titanium, or
other suitable metal, could be from about 10-50%, about 15-45%, or
even about 20-40%. In some embodiments, the atomic percentage of
aluminum could be less than about 15%, less than about 10%, or even
less than about 5%, and in some cases below about 1%, such as about
.about.0%. In some embodiments, the atomic percentage of silicon or
boron could be greater than about 25%, greater than about 35%, or
greater than about 45%. In some embodiments, the atomic percentage
of carbon could be less than about 20%, less than about 10%, or
less than about 5%, and in some cases below about 1%, even about
.about.0%.
[0091] In some embodiments, the total combined percentage of
silicon, boron and aluminum in the film comprises more than about
20%, preferably more than about 30% and more preferably more than
about 40% and, if desired, in some case more than about 45%.
[0092] A variety of compositions are possible. For example, in some
embodiments it may be desirable to fabricate a thin film having a
composition where only one or some elements fall into any of the
"preferable," "more preferable," or "most preferable" ranges.
[0093] In some embodiments of the present disclosure, the disclosed
deposition methods can be used to form various stacks including,
but not limited to, NMOS stacks in the process of making a gate.
For example, in some embodiments, NMOS stacks containing TiC thin
films fabricated using the methods disclosed herein exhibit a
leakage (J.sub.g) (at -1V stress,) of less than about 10.sup.-2
A/cm.sup.2, less than about 10.sup.-3 A/cm.sup.2, or less than
about 3*10.sup.-4 A/cm.sup.2.
[0094] In some embodiments of the present disclosure, titanium
carbide (TiC) films can be formed in dielectric/metal stack in
which the equivalent oxide thickness, or EOT, of the stack can be
less than about 1.3 nm, less than about 1.2 nm, preferably less
than about 1.1 nm, or less than about 1.05 nm.
[0095] In some embodiments of the present disclosure, TiC films can
be formed in which the effective workfunction, or eWF, can be from
about 4.0 to about 4.4 eV, from about 4.05 to about 4.35 eV, or
from about 4.1 to about 4.25 eV.
[0096] In some embodiments, the use of a silane/borane agent such
as a silane (e.g., disilane or trisilane) can reduce the
resistivity of a TiC thin film relative to a TiC film to which a
silane/borane agent is not exposed. In some embodiments, the
resistivity is reduced up to or as much as about 30%, up to or as
much as about 40%, or up to or as much as about 50%.
[0097] Use of a silane/borane agent as disclosed herein also has
the potential of providing a thin film, such as a TiC, with
resistance to oxidation. In some embodiments, it is believed,
without being held to any theory, that resistance to oxidation has
been increased even when the films are subjected to subsequent
processing or the atmosphere. Without being tied to any particular
theory, it is believe that resistance to oxidation is reduced
because the silane/borane agents tend to decrease the amount of
carbon in the thin film as it is partially replaced by silicon or
boron or some other element comprising the silane/borane agent.
[0098] Oxidation resistance is important because even a minor
amount of oxygen in the stack could change the stack's electrical
properties, namely eWF, making them unsuitable for intended
purposes. Moreover, deposition of the stack without exposure to air
or ambient moisture can be costly, difficult, and/or too complex.
Thus, achieving the same or similar results using a silane/borane
agent greatly simplifies deposition process while also controlling
costs.
Semiconductor Device Applications
[0099] Methods of fabricating semiconductor device structures will
now be discussed. Although described in terms of several specific
contexts, one of skill in the art will recognize that the processes
described herein are applicable to many other contexts as well.
[0100] The ALD processes disclosed herein may be successfully
applied to fabricate NMOS transistors including planar devices as
well as multiple gate transistors, such as FinFET.
Carbon-Containing Films as Electrodes
[0101] In some embodiments an electrode is formed by ALD of a
conductive metal carbide, such as TiC. With reference to FIG. 2, a
layer of high-k dielectric material 200 is deposited onto a
substrate (not shown). The substrate may be treated prior to
deposition of the high-k material. For example, in some
embodiments, a thin interfacial layer (not shown) may be deposited
prior to deposition of the high-k material. In one embodiment a
thin chemical oxide or oxynitride is formed on the surface. In
other embodiments a thermal oxide is grown on the substrate.
[0102] "High-k" generally refers to a dielectric material having a
dielectric constant (k) value greater than that of silicon oxide.
Preferably, the high-k material has a dielectric constant greater
than 5, more preferably greater than about 10. Exemplary high-k
materials include, without limitation, HfO.sub.2, ZrO.sub.2,
Al.sub.2O.sub.3, TiO.sub.2, Ta.sub.2O.sub.5, Sc.sub.2O.sub.3,
lanthanide oxides and mixtures thereof, silicates and materials
such as YSZ (yttria-stabilized zirconia), barium strontium titanate
(BST), strontium titanate (ST), strontium bismuth tantalate (SBT)
and bismuth tantalate (BT). Preferably, the high-k material is also
deposited by an ALD process.
[0103] A layer or thin film 210 of a material such as TiN may be
deposited over the dielectric layer. Such a layer may act as an
etch stop layer in which the etching has been previously performed
in another reactor or in a other facility altogether. The transfer
from one reactor or facility to another can expose the thin films
to contaminants such as water or air. The water or air generally
oxidizes any exposed layer such as TiN transforming the layer into
essentially TiON. Such contamination can interfere with the
workfunction of the eventual stack.
[0104] A layer or thin film of conductive metal carbide 220, such
as TiC, is deposited over the layer 210 by ALD, as described above,
to form the illustrated structure. It will be appreciated that in
the illustrated embodiment the layers are not necessarily drawn to
scale. The metal carbide, thin layer of TiN, and underlying high-k
material are patterned to form an electrode.
[0105] The metal carbide thin film 220 is preferably deposited over
the thin film 210 by contacting the substrate with alternating
pulses of a metal source chemical, carbon source chemical and a
silane/borane agent (not necessarily in this order) or by
depositing a complete metal carbide film by ALD and then treating
the resulting film with a silane/borane agent, as described above.
The metal source chemical is preferably a halide compound (e.g.,
TiCl.sub.4) and the carbon source chemical is preferably an
organometallic compound, such as, e.g., trimethylaluminum
(TMA).
[0106] In some embodiments, the thin layer of TiN is treated with a
silane/borane agent. This can be done in addition to treating the
metal carbide film with a silane/borane agent or forming the metal
carbide film utilizing a silane/borane agent. The silane/borane
agent can reduce the thin film 210. If comprising TiON, a
silane/borane agent reduces the thin film back to essentially TiN.
In this manner the work function may be improved or maintained as
what it was before the oxidation occurred. And the presence of the
silane/borane agent in the resulting carbide layer can actually
provide other benefits such as reduced resistivity. The
silane/borane agent may be selected from the group including
silanes (e.g., SiH.sub.4, Si.sub.2H.sub.6, or Si.sub.3H.sub.8) and
boranes (e.g., B.sub.2H.sub.6).
[0107] The thicknesses of the various layers in the stack may vary,
though in some embodiments, such as the one illustrated in FIG. 2,
layer 210 may have a thickness of about 10 .ANG. to about 20 .ANG.,
preferably about 15 .ANG.. And layer 220 may have a thickness
generally greater than the thickness of layer 210. The use of a
protective treatment as presently disclosed can have particular
utility where the thicknesses of the various layers in a stack,
such as the one illustrated in FIG. 2, are reduced to achieve
smaller electronic devices and circuitry. This is because thinner
layers are more prone to oxygen diffusing through them. And, in
some embodiments, the use of a silane/borane agent does not
appreciably increase the overall thickness of the stack.
[0108] When forming the metal carbide film, unreacted source
chemicals and reaction by-products are removed from the reaction
chamber after each source chemical pulse, for example by evacuation
and/or purging with an inert gas (e.g., N.sub.2). In some
embodiments, evacuation is achieved using a vacuum pump or a
plurality of vacuum pumps. The pulsing cycle, which can include a
silane/borane agent in at least some cycles, is repeated until a
metal carbide layer of the desired thickness has been formed. In
some embodiments, a silane/borane agent is also or only applied
after all the cycles have been completed. The silane/borane agent
may be applied either as a pulse or a soak. In some embodiments, it
may be preferably to apply the silane/borane agent as a soak after
all the cycles have been completed. And preferably, the metal
carbide layer has a thickness between about 5 .ANG. and about 1000
.ANG..
[0109] The conductive metal carbides deposited to form the
electrode in these embodiments are preferably selected from the
group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W.
[0110] In some embodiments the metal carbide forms the electrode.
In other embodiments (not shown) another conductive material, such
as a metal or poly-Si, is deposited over the metal carbide. The
additional conductive material may be deposited by ALD or by
another deposition process, such as by CVD or PVD. The deposition
may be selective, or may be followed by patterning steps. According
to still another embodiment, annealing can be performed after the
metal carbide deposition. Suitable atmospheres, such as N.sub.2 or
forming gas (N.sub.2/H.sub.2) are apparent to skilled artisan.
[0111] Further processing steps, such as spacer deposition and
source/drain implantation, will be apparent to the skilled
artisan.
Example 1
TiC Films
[0112] Using the methods disclosed here in, various titanium
carbide thin films were deposited. The thin film was then analyzed
using Rutherford backscattering spectrometry, or RBS, to determine
the composition of the various films.
[0113] After analyzing the various films, it was determined that
they the following ranges of compositions on an atomic basis: about
17-20% Ti, about 17-27% Al, about 16-42% Si, and about 21-39%
C.
Example 2
TiAlC and TiAlSiC in a single wafer reactor
[0114] Titanium-aluminium carbide (TiAlC) and
titanium-aluminum-carbide-silicon (TiAlSiC) thin films were
deposited by Atomic layer deposition (ALD) in Pulsar.RTM. 2000
R&D reactor using TiCl.sub.4 as the titanium source and
Al(CH.sub.2CH.sub.3).sub.3 as the aluminum and carbon source for
the TiAlC films and in addition disilane (Si.sub.2H.sub.6) or
trisilane (Si.sub.3H.sub.8) was used as a silicon source for
TiAlSiC films.
[0115] TiAlC and TiAlSiC films were deposited using alternate and
sequential pulses of TiCl.sub.4 and Al(CH.sub.2CH.sub.3).sub.3 and
in the case of TiAlSiC films additional alternate and sequential
pulses of disilane (Si.sub.2H.sub.6) or trisilane (Si.sub.3H.sub.8)
were provided. TiAlC films were also soaked with disilane
(Si.sub.2H.sub.6) or trisilane (Si.sub.3H.sub.8) for about 1
minute. Films were deposited and treated at a reaction temperature
of about 415.degree. C. TiCl.sub.4 was pulsed for 0.05 s and purged
for 5 s. Al(CH.sub.2CH.sub.3).sub.3 was pulsed for 0.5 s and purged
for 5 s. Si.sub.2H.sub.6 or Si.sub.3H.sub.8 was pulsed for 0.5 s
and purged for 5 s. The Al(CH.sub.2CH.sub.3).sub.3 was heated to
60.degree. C. and TiCl.sub.4 was at room temperature. Carrier gas
was ultrapure N.sub.2 and the flow used was 0.6 slm.
[0116] Some of the films were deposited on thermal SiO.sub.2/Si
substrates while others were deposited on 2-3 nm HfO.sub.2/0.4 nm
SiO.sub.2/Si substrate with or without a TiN intermediate layer (75
cycles) on top of a HfO.sub.2 layer. The TiN intermediate layer was
deposited before TiAlC or TiAlSiC film deposition. Substrates
having 2-3 nm HfO.sub.2/0.4 nm SiO.sub.2/Si and the optionally
deposited TiN intermediate layer were used to electrically
characterize the films. Further another TiN layer (250 cycles) was
deposited on top of the TiAlC or TiAlSiC layers. All TiN layers
were deposited using TiCl.sub.4 and NH.sub.3 as a precursors in the
same reaction chamber in which TiAlC or TiAlSiC film deposition
took place without moving the substrate out of the reaction
chamber. This resulted in a stack structure of 6-8 nm TiN/3-4 nm
TiAlSiC or TiAlC/(optional 2-2.5 nm TiN/) 2-3 nm HfO.sub.2/0.4 nm
SiO.sub.2/Si measured by transmission electron microscopy (TEM)
from the cross sectional area of the samples. After stack
depositions, platinum dots were deposited by physical vapor
deposition (PVD) on top of the samples, then the TiN, TiAlSiC, and
TiAlC layers were etched away from the area between the platinum
dots forming a capacitor array with circular top electrodes. These
capacitor structures were used to determine the effective work
function of the TiAlSiC or TiAlC layer, the equivalent oxide
thickness and the leakage current density of the stacks, which
represent important properties and quality of the films, although
results from capacitor structures might not be directly comparable
or transferrable to results of NMOS transistor structures.
[0117] The results and properties of the deposited TiAlC and
TiAlSiC films are shown in Table 2. The growth rate of the
deposited films ranged from about 2.55 to 3.8 .ANG./cycle on 20 nm
thermal SiO.sub.2/Si substrates and the resistivity ranged from
1300 to 3800 .mu..OMEGA.cm. It may be noted that the soak with
disilane or trisilane formed a silicon layer on top of the TiAlC
layer (though, the silane may also have penetrated or diffused
through a portion o the TiAlC layer or even the whole layer);
therefore the growth rate is not shown in the table. The films were
measured by Rutherford backscattering spectroscopy (RBS) to find
out elemental composition. The effective work functions (eWF) of
the TiAlC and TiAlSiC layers ranged from 4.20 to 4.33 eV, the
equivalent oxide thicknesses ranged from 1.04 to 1.20, and the
leakage current densities ranged from 5.17.times.10.sup.-3
A/cm.sup.2 to 1.69.times.10.sup.-5 A/cm.sup.2. Further it was
assumed that the stability against ambient oxygen in air or
oxidation or further (moisture and/or oxygen) might potentially
have been increased, believed to be true without being bound to any
theory, due to reduced carbon content in TiAlSiC films.
[0118] The results achieved with the TiAlSiC films made with
Si.sub.3H.sub.8, either incorporating Si.sub.3H.sub.8 into growth
cycles or with subsequent soaking of the film, were the most
desirable ones for end use in NMOS transistors, as those had lowest
effective work function and low resistivity while still maintaining
reasonably low leakage and low EOT and potentially good oxidation
resistance. Also the TiAlSiC films made with Si.sub.2H.sub.6 either
incorporating Si.sub.2H.sub.6 into growth cycles or with soaking
are acceptable or better than the TiAlC films because of the
increased oxidation resistance as explained above and the lower
resistivity.
TABLE-US-00001 TABLE 2 Properties of TiAlC and TiAlSiC films.
Growth rate Resistivity Composition Leakage at Film (.ANG./cycle)
(.mu..OMEGA.cm) (RBS) eWF (eV) EOT (nm) -1 V (A/cm.sup.2) TiAlC
3.14-3.80 3500-3800 Ti 18 at-%, 4.31-4.33 1.05-1.14 1.69 .times.
10.sup.-5-4.12 .times. 10.sup.-4 Al 38 at-%, C 42 at-%, H 2 at-%,
TiAlSiC + Si.sub.3H.sub.8 2.55-3.73 1300-1800 Ti 17 at-%, 4.20-4.28
1.11-1.20 1.01 .times. 10.sup.-4-5.17 .times. 10.sup.-3 Al 17-21
at-%, Si 26-42 at-% C 21-34 at-%, H 1 at-%, Cl 0.5-1 at-% TiAlSiC +
Si.sub.2H.sub.6 3.20-3.80 1400-2500 Ti 17-20 at-%, 4.30 1.04 3.05
.times. 10.sup.-4 Al 20-27 at-%, Si 16-24 at-%, C 35-39 at-%, H 1
at-%, Cl 0.5 at-% TiAlC + Si.sub.3H.sub.8 -- -- -- 4.24-4.33
1.12-1.19 2.94 .times. 10.sup.-4-4.80 .times. 10.sup.-3 soak for 60
s TiAlC + Si.sub.2H.sub.6 -- -- -- 4.32 1.06 1.64 .times. 10.sup.-4
soak for 60 s
[0119] In all of the aforesaid embodiments, any element used in an
embodiment can interchangeably be used in another embodiment unless
such a replacement is not feasible.
[0120] It will be understood by those of skill in the art that
numerous and various modifications can be made without departing
from the spirit of the present invention. Therefore, it should be
clearly understood that the forms of the present invention are
illustrative only and are not intended to limit the scope of the
present invention. All modifications and changes are intended to
fall within the scope of the invention, as defined by the appended
claims.
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