U.S. patent application number 11/166258 was filed with the patent office on 2005-10-20 for system and method for forming multi-component dielectric films.
This patent application is currently assigned to AVIZA TECHNOLOGY, INC.. Invention is credited to Park, Seung Gyun, Senzaki, Yoshihide.
Application Number | 20050233156 11/166258 |
Document ID | / |
Family ID | 33479703 |
Filed Date | 2005-10-20 |
United States Patent
Application |
20050233156 |
Kind Code |
A1 |
Senzaki, Yoshihide ; et
al. |
October 20, 2005 |
System and method for forming multi-component dielectric films
Abstract
The present invention provides systems and methods for mixing
precursors such that a mixture of precursors are present together
in a chamber during a single pulse step in an atomic layer
deposition (ALD) process to form a multi-component film. The
precursors are comprised of at least one different chemical
component, and such different components will form a mono-layer to
produce a multi-component film. In a further aspect of the present
invention, a dielectric film having a composition gradient is
provided.
Inventors: |
Senzaki, Yoshihide; (Aptos,
CA) ; Park, Seung Gyun; (Scotts Valley, CA) |
Correspondence
Address: |
Maria S. Swiatek
DORSEY & WHITNEY LLP
Suite 3400
4 Embarcadero Center
San Francisco
CA
94111
US
|
Assignee: |
AVIZA TECHNOLOGY, INC.
|
Family ID: |
33479703 |
Appl. No.: |
11/166258 |
Filed: |
June 24, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11166258 |
Jun 24, 2005 |
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10829781 |
Apr 21, 2004 |
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60464458 |
Apr 21, 2003 |
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60520964 |
Nov 17, 2003 |
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60560952 |
Apr 9, 2004 |
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Current U.S.
Class: |
428/446 ;
257/E21.267; 257/E21.269; 257/E21.278; 257/E21.279 |
Current CPC
Class: |
H01L 21/02164 20130101;
H01L 21/0214 20130101; H01L 21/02181 20130101; H01L 21/3145
20130101; H01L 21/31645 20130101; H01L 21/3142 20130101; H01L
21/31608 20130101; H01L 21/31612 20130101; H01L 21/02205 20130101;
C23C 16/45531 20130101; H01L 21/3141 20130101; H01L 21/0228
20130101; C23C 16/401 20130101; H01L 21/0217 20130101; H01L
21/02337 20130101; C23C 16/308 20130101; H01L 21/3143 20130101;
H01L 21/02148 20130101; C23C 16/029 20130101 |
Class at
Publication: |
428/446 |
International
Class: |
B32B 009/04; B32B
013/04; H01L 021/31; H01L 021/469 |
Claims
What is claimed:
1. A method of forming a film on a surface of a substrate,
characterized in that: two or more precursors, each of the
precursors containing at least one different chemical component,
are conveyed to a process chamber together and form a mono-layer on
the surface of the substrate, said mono-layer containing each of
the separate chemical components, said process chamber being
configured to house a plurality of substrates.
2. The method of claim 1 wherein said substrate surface is selected
from the group consisting of silicon, plastics, polymers, metals,
alloys, organics, inorganics, or mixtures thereof.
3. The method of claim 1 where the precursors have the formula:
M(L)x where M is a metal selected from the group of: Ti, Zr, Hf,
Ta, W, Mo, Ni, Si, Cr, Y, La, C, Nb, Zn, Fe, Cu, Al, Sn, Ce, Pr,
Sm, Eu, Th, Dy, Ho, Er, Tm, Yb, Lu, Ga, In, Ru, Mn, Sr, Ba, Ca, V,
Co, Os, Rh, Ir, Pd, Pt, Bi, Sn, Pb, Tl, Ge or mixtures thereof;
where L is a ligand selected from the group consisting of amine,
amides, alkoxides, halogens, hydrides, alkyls, asides, nitrates,
nitrites, cyclopentadienyls, carbonyl, carboxylates, diketonates,
alkenes, alkynes, or a substituted analogs thereof, and
combinations thereof; and where x is an integer less than or equal
to the valence number for M.
4. The method of claim 1 further comprising supplying at least one
reactant that reacts with said monolayer.
5. The method of claim 4, wherein said at least one reactant is
delivered sequentially or simultaneously with the precursors.
6. The method of claim 4, wherein said at least one reactant is a
nitridating reactant, reducing reactant, oxidizing reactant, or a
mixture thereof.
7. The method of claim 6, wherein said nitridating reactant is
selected from the group consisting of ammonia, deuterated ammonia,
15N-ammonia, amines or amides, hydrazines, alkyl hydrazines,
nitrogen gas, nitric oxide, nitrous oxide, nitrogen radicals,
N-oxides, or mixtures thereof.
8. The method of claim 6, wherein said oxidizing reactant is
selected from the group consisting of ozone, oxygen, singlet
oxygen, triplet oxygen, atomic oxygen, water, peroxides, air,
nitrous oxide, nitric oxide, H.sub.2O.sub.2, and mixtures
thereof.
9. A method for forming a multi-component film on a surface of a
substrate comprising the steps of: vaporizing two or more
precursors, each of the precursors containing at least one metal or
metalloid component; conveying the two or more precursors into a
process chamber configured to house a plurality of substrates,
wherein the precursors are present together in the process chamber;
forming a mono-layer on the surface of the substrate, said
mono-layer containing each of the metal or metalloid components;
and purging said process chamber.
10. The method of claim 9 wherein said forming step is carried out
at a temperature in the range of approximately 20 to 800 C.
11. The method of claim 9 wherein said process chamber is at a
pressure in the range of approximately 0.001 mTorr to 600 Torr.
12. The method of claim 9 wherein the step of conveying further
includes mixing the two or more precursors and conveying the
mixture of precursors into the process chamber.
13. The method of claim 9, wherein said purging step further
comprises introducing a carrier gas to evacuate the precursors from
the chamber.
14. The method of claim 9 further comprising conveying a reactant
gas to the process chamber, wherein the reactant gas contacts the
mono-layer formed on the surface of the substrate.
15. The method of claim 14 wherein the gas flow rate to the process
chamber is in the range of approximately 0 to 20,000 sccm.
16. The method of claim 9 where the precursors have the formula:
M(L)x where M is a metal selected from the group of: Ti, Zr, Hf,
Ta, W, Mo, Ni, Si, Cr, Y, La, C, Nb, Zn, Fe, Cu, Al, Sn, Ce, Pr,
Sm, Eu, Th, Dy, Ho, Er, Tm, Yb, Lu, Ga, In, Ru, Mn, Sr, Ba, Ca, V,
Co, Os, Rh, Ir, Pd, Pt, Bi, Sn, Pb, Tl, Ge or mixtures thereof;
where L is a ligand selected from the group consisting of amine,
amides, alkoxides, halogens, hydrides, alkyls, asides, nitrates,
nitrites, cyclopentadienyls, carbonyl, carboxylates, diketonates,
alkenes, alkynes, or a substituted analogs thereof, and
combinations thereof; and where x is an integer less than or equal
to the valence number for M.
17. A system for atomic layer deposition comprising: at least a
first vaporizer containing a first deposition precursor for
deposition; a least a second vaporizer containing a second
deposition precursor for deposition; a process chamber configured
to house a plurality of substrates and adapted to carry out an
atomic layer deposition process; and a manifold, said manifold
being coupled to said first and second vaporizers and to said
process chamber, said manifold being adapted to mix and convey the
first and second deposition precursors to said process chamber.
18. The system of claim 17, wherein said process chamber further
comprises: a gas inlet coupled to said manifold; and an inlet for
supplying at least one reactant gas, wherein said inlet provides
said at least one reactant in said process chamber in-situ in
either sequential or simultaneous manner.
19. The method of claim 1 wherein said monolayer is selected from
the group consisting of metals and metal, metal alloy or mix metal
oxides, silicates, nitrides and oxynitrides.
20. The method of claim 1 wherein each said monolayer is
compositionally variable and electrically and physically compatible
with the adjacent said monolayers.
21. A method of forming a film on the surface of a substrate,
characterized in that: two or more precursors, each of the
precursors containing at least one different chemical component,
are conveyed to a process chamber together and form a mono-layer on
the surface of the substrate, said process chamber being configured
to house a plurality of substrates and wherein the amount of each
of the precursors conveyed to the process chamber is selectively
controlled such that a desired composition gradient of one of more
of the chemical components is formed in the film.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation Application of U.S.
patent application Ser. No. 10/829,781 filed Apr. 21, 2004,
entitled "System and Method for Forming Multi-Component Dielectric
Films" which claims the benefit of, and priority to, each of U.S.
provisional patent application Ser. No. 60/464,458 filed on Apr.
21, 2003 entitled Fabrication Method of Multi-Component Films; U.S.
provisional patent application Ser. No. 60/520,964 filed Nov. 17,
2003 entitled ALD of HfSiON with Controlled Thickness and
Composition Gradient; and U.S. provisional patent application Ser.
No. 60/560,952 filed Apr. 9, 2004 entitled Atomic Layer Deposition
of Metal or Mixed Metal Thin Films, the entire disclosures of each
of which are incorporated by reference herein.
FIELD OF THE INVENTION
[0002] In general, the present invention relates to systems and
methods for forming dielectric films in semiconductor applications.
More specifically, the present invention relates to systems and
methods for fabricating multi-component dielectric films on a
substrate using mixed vaporized precursors.
BACKGROUND OF THE INVENTION
[0003] Concurrent with the increase in sophistication and drive
towards miniaturization of microelectronics, the number of
transistors per integrated circuit has exponentially grown and
promises to grow to meet the demands for faster, smaller and more
powerful electronic systems. However, as traditional silicon-based
transistor geometries reach a critical point where the silicon
dioxide gate dielectric becomes just a few atomic layers thick,
tunneling of electrons will become more prevalent leading to
current leakage and increase in power dissipation. Accordingly, an
alternative dielectric possessing a higher permittivity or
dielectric constant than silicon dioxide and capable of preventing
current tunneling or leakage would be highly desirable. Among the
most promising dielectric candidates to replace silicon dioxide
includes hafnium oxide, zirconium oxide and tantalum oxide.
[0004] Unfortunately, these materials are chemically and thermally
unstable on silicon, unlike silicon dioxide, forming defects and
charge traps at the interface between the metal dielectric and the
silicon substrate. The charge traps and defects absorb the voltage
applied at the gate and perturb the performance and reliability of
the transistor. To limit the formation of interfacial charge traps
and defects, an interfacial layer of silicon dioxide is deposited
in between the dielectric and the silicon substrate. The silicon
dioxide interface buffers the silicon substrate from the
dielectric, but the silicon dioxide interface may not be compatible
with the surface properties of the dielectric. Accordingly, an
interface that can ameliorate the surface properties and
chemistries of the dielectric and silicon substrate, while
minimizing the equivalent physical oxide thickness, is needed to
fabricate ultra-thin high k dielectrics.
[0005] Prior art deposition techniques for fabricating films such
as chemical vapor deposition (CVD) are increasingly unable to meet
the requirements of advanced thin films. While CVD processes can be
tailored to provide conformal films with improved step coverage,
CVD processes often require high processing temperatures. For
instance, one of the obstacles of making high k gate dielectrics is
the formation of an interfacial silicon oxide layer during CVD
processes. Gas phase reaction in CVD leads to particle generation.
Another obstacle is the limitation of prior art CVD processes in
depositing ultra thin films for high k gate dielectrics on a
silicon substrate.
[0006] An alternative to traditional CVD processes to deposit very
thin films is Atomic layer deposition (ALD). ALD has several
advantages over traditional CVD. ALD can be performed at
comparatively low temperatures which is compatible with the
industry's trend toward lower temperatures, and can produce
conformal thin film layers. he existing method for depositing
multi-component films, such as a HfxSiyO.sub.2(x+y=1) film, using
an ALD processes is to deposit laminate films of HfO.sub.2 and
SiO.sub.2 film using a sequential vapor deposition method. That is,
the precursor chemicals are not mixed, and instead an Hf containing
precursor and a Si containing precursor are pulsed independently
and sequentially into the chamber to form laminate layers of HfO
and SiO.sub.2, respectively. In fact, any mixing of precursors is
prohibited, and the chamber is purged of one precursor before the
second precursor is pulsed. Once the laminate films are formed to a
desired thickness, the film is annealed in an attempt to arrive at
more continuous composition throughout the film. This approach of
building up layers of different laminate films leads to many
electron traps in the film due to the multiple interfaces which
requires high temperature thermal anneal to fix the traps. The
addition of the high temperature thermal annealing step increases
cost and time for manufacturing semiconductors, and moreover can
result in the undesirable out migration of elements from previously
formed layers on the wafer. In addition, it is difficult to control
the stoichiometric composition of multi-component films in the
laminate method. The dielectric constant (k), crystallization
temperature and refractive index of HfSiOx films cannot be easily
controlled by the traditional one chemical sequential precursor
pulse methods (such as the laminate method). Furthermore, the cycle
times needed to form a film of desired thickness using the
conventional sequential pulse and purge of one chemical precursor
at a time are impractical and require too much time for future IC
manufacturing.
[0007] Attempts to fabricate a multi-component films using mixed
precursors have been limited to the traditional CVD methods. For
example, U.S. Pat. Nos. 6,537,613 and 6,238,734 both to Senzaki et
al. (the '613 and '734 patents) generally disclose system and
methods for generating a compositional gradient comprising a metal
and metalloid compound by direct liquid injection. In direct liquid
injection (DLI), the metal and metalloid precursors are mixed
together to form a solventless liquid mixture prior to injection of
the mixture into the deposition system.
[0008] There are however several drawbacks associated with the
method described in the '613 and '734 patents. Specifically, it is
a liquid mixture that is injected. As such, if the liquid mixture
is not thoroughly mixed, a film having an uneven composition and
gradient will form on the substrate. In addition, even if
appropriate volumes of samples are provided, there is no guarantee
that the mixture will vaporize uniformly since each precursor has a
unique boiling point, vapor pressure and volatility. Furthermore,
if the discrepancy in boiling points between the precursors is
substantial, one precursor may decompose at the boiling point of
the second forming particulates or contaminants. Generally, either
the precursors have not been adequately mixed, resulting in a
non-uniform film composition, or mixing of the two vapors causes
pre-reaction in the gas phase, resulting in the formation of
particles or contaminants that are deposited on the wafer.
[0009] Accordingly, there is a need for further developments in
methods of fabricating multi-component films. There is particularly
a need for a method of fabricating multi-component films using an
ALD process. It is further desirable that the method provides
control of the stoichiometric composition or gradient of a
multi-component film.
BRIEF SUMMARY OF THE INVENTION
[0010] In general, the inventors have discovered a method that
provides for mixing vaporized precursors such that a mixture of
vaporized precursors are present together in a chamber during a
single deposition or pulse step in an atomic layer deposition (ALD)
process to form a multi-component film. The vaporized precursors
are each comprised of at least one different chemical component,
and such different components will form a mono-layer to produce a
multi-component film. The inventors refer to this method as
"co-injection ALD." Such a method is a departure from the prior
art, where the vaporized precursors are pulsed separately into the
chamber in the ALD process to form separate mono-layers containing
only one of the components.
[0011] One aspect of the present invention provides systems and
methods for fabricating multi-component dielectric films by mixing
vaporized precursors together and then injecting or co-injecting
the vaporized precursors such that a mixture of precursors are
present in the ALD chamber. As used herein the term
"muti-component" film means that the film contains two or more
metal or metalloid elements. A variety of multi-component films may
be formed by the present invention, including but not limited to:
metal, metal alloy, mixed metal oxides, silicates, nitrides,
oxynitrides, and mixtures thereof.
[0012] In one embodiment of the present invention, a method of
forming a thin film on a surface of a substrate by atomic layer
deposition is provided, characterized in that: two or more
vaporized precursors each of the precursors containing at least one
different chemical component (typically a metal or metalloid
element), are conveyed into a process chamber together to form a
mono-layer on the surface of the substrate, and said mono-layer
contains each of the separate chemical components. In general the
term co-injecting is used to mean that two or more precursors
having at least one different chemical component are present in a
chamber such that a film is produced having multiple components.
This may be accomplished by injecting or conveying precursors
together in either vapor or liquid state (aerosol) into a process
chamber, or mixing the precursors in the process chamber. Mixing of
the precursors prior to introduction into the process chamber is
preferred, but not required.
[0013] In another aspect the present invention provides a system
for forming multi-component films. In one embodiment, the system
generally includes one or more vaporizers, each vaporizer being
coupled to a manifold. The manifold is configured to mix the
vaporized precursors generated by the vaporizers. The manifold is
coupled to an inlet to a process chamber and the mixed precursors
are injected into the chamber through the inlet. In one embodiment
the inlet is comprised of an injector, such as a showerhead
injector. It is possible that the precursors may be mixed in the
injector, and not in a manifold.
[0014] In yet another aspect of the present invention, a system and
method is provided for forming a multi-component film having a
compositional gradient. In one embodiment a method of forming a
multi-component film is provided characterized in that two or more
vaporized precursors each of the precursors containing at least one
different chemical component, are injected into a process chamber
together to form a mono-layer on the surface of the substrate,
wherein the gas flow rate of each of the vaporized precursors
injected into the chamber are selectively controlled such that a
desired composition gradient of one or more of the different
chemical components is formed in the film.
[0015] In a further aspect of the present invention, a dielectric
film having a composition gradient is provided comprising: a
silicon-rich bottom layer, a nitrogen-rich top layer, and at least
one hafnium-rich layer between said top and bottom layers. In one
embodiment nitrogen is deposited selectively near or above a
silicon substrate-dielectric interface to deter boron diffusion. In
further embodiments, it is desirable to provide system and methods
for deterring boron diffusion without placing a burden on the
equivalent physical oxide thickness of the dielectric and quality
of the interface between the silicon and the nitride dielectric,
leading, for example, to higher trap densities. In one embodiment,
a compositional gradient may be used to "buffer" the dielectric and
the substrate. For example, when the substrate is silicon, a first
layer is deposited rich in silicon and lesser amounts of a second
deposition metal that makes up the dielectric. Atop the first
layer, a second layer comprising predominantly a deposition metal
that makes up the dielectric is deposited in addition to
substantial lesser amounts of silicon. In some embodiments,
additional layers can be added to blend the surface properties and
chemistries of the adjacent layers. In various embodiments, each
layer can be oxidized, reduced, nitridated, or a combination
thereof in-situ.
[0016] Further, the invention provides systems and methods for
fabricating multi-component oxynitride films, wherein a
multi-component film is formed by the method described above, and
then the film is oxidized at elevated temperatures with an
oxidizing reactant selected from the group consisting of ozone,
oxygen, peroxides, water, air, nitrous oxide, nitric oxide,
N-oxides, or mixtures thereof. Of particular advantage, the
oxidation step can be preformed in-situ. Following oxidation, an
excited nitrogen source is sequentially conveyed to the process
chamber and permitted to react with the oxidized layer at elevated
temperatures to form an oxynitride. Again, this step is performed
in-situ.
[0017] In a preferred embodiment, the invention provides systems
and methods for fabricating multi-component oxynitride films by
mixing precursors that contain a nitridating reactant into the
chamber and carrying our the ALD process at relatively low
temperatures. Suitable nitridating agents can be selected from the
group consisting of ammonia, deuterated ammonia, .sup.15N-ammonia,
amines or amides, hydrazines, alkyl hydrazines, nitrogen gas,
nitric oxide, nitrous oxide, nitrogen radicals, N-oxides, or
mixtures thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Other aspects, embodiments and advantages of the invention
will become apparent upon reading of the detailed description of
the invention and the appended claims provided below, and upon
reference to the drawings in which:
[0019] FIG. 1 is a schematic block diagram of an system for
fabricating a multi-component, multi-layered film in accordance
with one embodiment of the present invention.
[0020] FIG. 2 is a cross-section al view of a high k dielectric
gate material formed utilizing system and methods of the present
invention.
[0021] FIG. 3 is a flow chart illustrating the method for
fabrication of the compositional gradient films according to one
embodiment of the present invention.
[0022] FIG. 4 illustrates the relationship between film composition
and the deposition precursor gas flow rates. In this particular
example, the deposition and composition of hafnium-silicon films
can be modified by controlling the hafnium and silicon deposition
gas flow rates.
[0023] FIG. 5 tabulates the results of the atomic compositional
analysis of various HfSiO films fabricated by the system and method
of the present invention. The results indicate that over a given
hafnium and silicon content concentration, the ratio of oxygen
atoms to hafnium and silicon atoms is approximately 2. These
results indicate that the HfSiO films fabricated by system and
methods of the present invention, over a particular range, affords
films having the structural formula Hf.sub.xSi.sub.1-xO.sub.2. The
percentage of carbon, hydrogen and nitrogen is only found in trace
amounts.
[0024] FIGS. 6a and 6b show X-Ray Photoelectron Spectroscopy (XPS)
spectra of a film having the formula Hf.sub.0.5Si.sub.0.5O.sub.2
generated by the system and method of the present invention. In
particular, FIG. 6a highlights the XPS spectrum of the 4f region of
hafnium found in the film. FIG. 6b highlights the XPS spectrum of
the 2p region of silicon found in the film. In both spectra, very
little or no impurities can be seen.
[0025] FIG. 7 depicts the index of refraction for various 50 nm
thick Hf.sub.xSi.sub.1-xO.sub.2 films on silicon wafers measured as
a function of the Hf/(Hf+Si) ratios. The graph compares the index
of refraction for as-deposited and post-deposition annealed
films.
[0026] FIG. 8 illustrates the change in deposition rates for
Hf.sub.xSi.sub.1-xO.sub.2 films, resulting from the oxidation of
hafnium-silicon films with ozone, with respect to the deposition
temperature.
[0027] FIGS. 9a-9c shows various TEM cross-sectional images of
Hf.sub.0.58Si.sub.0.42O.sub.2 films deposited at 400.degree. C. on
HF last treated silicon substrates. FIGS. 9a, 9b and 9c show the
TEM images of Hf.sub.0.58Si.sub.0.42O.sub.2 films having a
dielectric thickness of 2.3 nm, 4.3 nm and 6.5 nm, respectively. In
each case, the thickness of the interface measures approximately 1
nm.
[0028] FIG. 10 is cross-sectional TEM image of
Hf.sub.0.58Si.sub.0.42O.sub- .2 with polysilicon cap layer after an
anneal at 700.degree. C. in N.sub.2.
[0029] FIG. 11 measures the capacitance equivalent thickness (CET)
and the leakage current density as a function of hafnium content
for various Hf.sub.xSi.sub.1-xO.sub.2 films on HF-last silicon
wafers.
[0030] FIG. 12 measures the film tensile stress as a function of
temperature for a 50 nm thick Hf.sub.0.34Si.sub.0.66O.sub.2
film.
[0031] FIG. 13 shows the X-ray Photoelectron Spectroscopy (XPS)
spectra for nitrogen 1s and hafnium 4P.sub.3/2 regions for an HfSiO
film nitridated with ammonia in a post-deposition annealing step.
Relative to HfSiO, the XPS spectra of an HfSiON film at various
take-off angles (TOA) reveal the presence of nitrogen in the
film.
[0032] FIG. 14 is a graph of the deposition rate of HfO.sub.2,
generated from the oxidation of hafnium dialkyl amide with ozone,
as a function of deposition temperature.
[0033] FIG. 15 is a cross-sectional view of a thin film having a
compositional gradient formed by the co-injection system and method
of the present invention. FIG. 15 show thin films, fabricated
sequentially and in-situ, comprising HfSiOx, HfO2 and HfOxNy or
HfSiON layers.
[0034] FIGS. 16a and 16b illustrate reaction schemes that describes
the two different ways to generate metal, metal alloy or mix metal
oxynitrides of the present invention. FIG. 16a shows a relatively
high temperature process for generating oxynitrides, wherein the
oxidation step precedes the nitridation step. Whereas, in FIG. 16b,
the oxidation step is reserved until the film has been nitridated
under relatively low temperatures.
[0035] FIG. 17 shows the compositional profile below the surface of
a typical oxynitride film. Nitrogen concentration is greatest on
the surface of the film, and gradually decreases below the surface
until the HfO.sub.2 layer is reached. With further penetration into
the film, the concentration of HfO.sub.2 decreases giving away to
HfSiO.sub.x, until the interfacial layer of the silicon substrate
is reached.
DETAILED DESCRIPTION OF THE INVENTION
[0036] In general, the inventors have discovered a method that
provides for mixing precursors such that a mixture of precursors
are present in a chamber during a single pulse step in an atomic
layer deposition (ALD) process to form a mono-layer having multiple
chemical compounds on the surface of a substrate. The precursors
are comprised of different chemical components, and such components
will form the multi-component film. The inventors refer to this
method as "co-injection ALD." Such a method is a departure from the
prior art, where the vaporized precursors are conveyed or pulsed
separately into the chamber in the ALD process. A variety of
multi-component films may be formed by the present invention,
including but not limited to: metal, metal alloy, mixed metal
oxides, silicates, nitrides, oxynitrides, and mixtures thereof.
[0037] In one aspect the present invention provides a system and
method for reproducibly and substantially uniformly controlling the
stoichiometric composition of a multi-component film.
[0038] In a series of embodiments, the present invention provides a
system and method for fabricating dielectrics possessing a higher
permittivity or dielectric constant than silicon dioxide and
capable of preventing current tunneling or leakage. In another
aspect of the present invention provides a system and method for
fabricating an interface that can ameliorate the surface properties
and chemistries of the dielectric and silicon substrate, while
minimizing the equivalent physical oxide thickness.
[0039] Accordingly, in some embodiments and aspects of the present
invention, the present invention provides system and methods for
depositing nitrogen selectively near or above the silicon
substrate-dielectric interface to deter boron diffusion and
increase the crystallization temperature of high-k layers. In
further embodiments, it is desirable to provide system and methods
for deterring boron diffusion without placing a burden on the
equivalent physical oxide thickness of the dielectric and quality
of the interface between the silicon and the nitride dielectric,
leading, for example, to higher trap densities.
[0040] In typical embodiments of the present invention, it is
desirable to provide a system and method for conducting low
temperature nitridation of films; and in another aspect of the
present invention, the present invention provides system and
methods for delivering a nitrogen reactant sequentially, in-situ,
eliminating the need for external plasmas sources and benefiting
from less processing steps and time.
[0041] In another aspect the present invention provides a system
for forming multi-component films. In one embodiment, the system
generally includes one or more vaporizers, each vaporizer being
coupled to a manifold. The manifold is coupled to an inlet to a
reaction or deposition chamber, said inlet being comprised of an
injector, such as a showerhead injector, and the like.
[0042] Each vaporizer holds a single deposition precursor
comprising at least one deposition metal. Each vaporizer is
connected to a mass flow controller and temperature control unit.
The mass flow controller and temperature unit may be selectively
controlled to moderate the concentration of deposition precursors
present in the process chamber. In one embodiment, each mass flow
controller moderates the flow of carrier gas through the system,
and, in turn, the carrier gas dilutes and transports the deposition
precursor into the manifold or process chamber.
[0043] In some series of embodiments, the vaporizer is a bubbler
that vaporizes a single deposition precursor comprising at least
one deposition metal. A pressurized gas including the carrier gas
is bubbled into the deposition precursor. The flow rate of the
pressurized gas may be selectively controlled to adjust the
concentration of the deposition precursor present in the process
chamber.
[0044] In one embodiment, a manifold facilitates mixing of the
deposition precursors prior to delivery into the process chamber.
In some embodiments, the manifold contains a T-junction cavity that
accommodates and mixes the deposition precursors prior to delivery
into the process chamber. The manifold may be heated to facilitate
the flow of deposition precursors into the process chamber so as to
prevent condensation in the manifold. Alternatively, mixing of the
precursors may take place in the process chamber and the manifold
may be eliminated.
[0045] The deposition precursor is delivered to the process chamber
typically via a gas inlet and a monolayer of deposition precursor
is chemi and/or physi absorbed on the surface or the substrate. The
substrate can be silicon, metal, metal alloy, glass or polymeric,
plastic, organic or inorganic work pieces. The gas inlet may take a
variety of forms. In one example the gas inlet is comprised of an
injection, such as a showerhead injector and the like.
Alternatively, the deposition precursor is delivered to the
substrate surface by a plurality of injectors.
[0046] Generally, the substrate is supported on a wafer support
such as an electrostatic or vacuum chuck during deposition when a
single wafer chamber is used. In one embodiment, the chuck is
capable of cooling or heating the substrate by conduction,
convection, radiative or non-radiative processes, or a mixture
thereof. Alternatively, a the wafer support may be a boat or
cassette which supports a plurality of substrates for batch
processing.
[0047] An inlet port switchably provides oxidizing, reducing or
nitridating reactants into the process chamber in-situ so as to
promote sequential oxidation, reduction or nitridation of the
monolayer or substrate surface.
[0048] In another aspect of the present invention, a dielectric
film having a composition gradient is provided comprising: a
silicon-rich bottom layer, a nitrogen-rich top layer, and at least
one hafnium-rich layer between said top and bottom layers. In one
embodiment nitrogen is deposited selectively near or above the
silicon substrate-dielectric interface to deter boron diffusion. In
further embodiments, it is desirable to provide a system and method
for deterring boron diffusion without placing a burden on the
equivalent physical oxide thickness of the dielectric and quality
of the interface between the silicon and the nitride dielectric,
leading, for example, to higher trap densities.
[0049] The invention further provides a system and method for
fabricating multi-component oxynitride films, wherein the
multi-component film is formed by the method described above, and
then the film is oxidized at elevated temperatures with an
oxidizing reactant selected from the group consisting of ozone,
oxygen, peroxides, water, air, nitrous oxide, nitric oxide,
H.sub.2O.sub.2, N-oxides, or mixtures thereof. Of particular
advantage, the oxidation step can be preformed in-situ. Following
oxidation, an excited nitrogen particle is sequentially conveyed to
the process chamber and permitted to react with the oxidized layer
at elevated temperatures to form an oxynitride. Again, this step is
performed in-situ.
[0050] The invention provides a system and method for fabricating
multi-component oxynitride films by mixing precursors that contain
a nitridating reactant into the chamber and carrying our the ALD
process at relatively low temperatures. Suitable nitridating agents
can be selected from the group consisting of ammonia, deuterated
ammonia, .sup.15N-ammonia, amines or amides, hydrazines, alkyl
hydrazines, nitrogen gas, nitric oxide, nitrous oxide, nitrogen
radicals, N-oxides, atomic nitrogen or mixtures thereof.
[0051] Of particular advantage, he multi-component film of the
invention is formed with a compositional gradient. A compositional
gradient may be used to "buffer" the dielectric and the substrate.
For example, when the substrate is silicon, a first layer is
deposited rich in silicon and lesser amounts of a second deposition
metal that makes up the dielectric. Atop the first layer, a second
layer comprising predominantly a deposition metal that makes up the
dielectric is deposited in addition to substantial lesser amounts
of silicon. In some embodiments, additional layers can be added to
blend the surface properties and chemistries of the adjacent
layers. In various embodiments, each layer can be oxidized,
reduced, nitridated, or a combination thereof in-situ. The
composition gradient also provides refractive index gradient in the
films, which provide unique optical properties of the films.
[0052] FIG. 1 is a simplified schematic diagram depicting a one
embodiment of a system for fabricating a multi-component film in
accordance with one embodiment of the present invention. Referring
to FIG. 1, in general the system 100 comprises a process chamber
102 which houses wafer support 110 for supporting a wafer or
substrate 112. A gas inlet 114 is provided for conveying deposition
precursors and other gases 103 (for example, reactant gases such as
oxidation gases and the like, or dilution gases) into the chamber
102 to form various layers or films on the surface of the
substrate. In the illustrative embodiment, a gas manifold 104
interconnects one or more vaporizers 107, 109 to the process
chamber 102. The illustrative embodiment shows two vaporizers
however, any number of vaporizes may be employed. Each vaporizer
comprises a reservoir 116, 118 for holding a deposition precursor
or a mixture of deposition precursors 124, 126, respectively, and a
vaporizer element 120, 122 through which a carrier gas is flowed to
assist in vaporizing the contents in reservoirs 116,118. The flow
of carrier gas into the vaporizers may be adjusted using a mass
flow controller (not shown) to control the rate and concentration
of the deposition precursors vaporized. Optionally, each vaporizer
may be equipped with a heating element (not shown) to facilitate
vaporization of the deposition precursors 124, 126 held in
reservoirs 116, 118. Depending on the physical characteristics of
the deposition precursors 124, 126, a combination of carrier gas
and heating may be required to vaporize the deposition precursors
in reservoirs 116, 118.
[0053] In one embodiment of the present invention, deposition
precursors comprising at least one deposition metal are used having
the formula:
M(L).sub.x
[0054] where M is a metal selected from the group consisting of Ti,
Zr, Hf, Ta, W, Mo, Ni, Si, Cr, Y, La, C, Nb, Zn, Fe, Cu, Al, Sn,
Ce, Pr, Sm, Eu, Th, Dy, Ho, Er, Tm, Yb, Lu, Ga, In, Ru, Mn, Sr, Ba,
Ca, V, Co, Os, Rh, Ir, Pd, Pt, Bi, Sn, Pb, Tl, Ge or mixtures
thereof; where L is a ligand selected from the group consisting of
amine, amides, alkoxides, halogens, hydrides, alkyls, azides,
nitrates, nitrites, cyclopentadienyls, carbonyl, carboxylates,
diketonates, alkenes, alkynes, or a substituted analogs thereof,
and combinations thereof; and where x is an integer less than or
equal to the valence number for M.
[0055] It is beneficial to select the ligands (L) to be the same in
each of the deposition precursors to avoid ligand exchange from
taking place when each of the precursors is mixed in vaporous form.
Ligand exchange can lead to the formation of particulates that can
adversely effect the quality of the deposited film. Ligands that do
not undergo ligand exchange in vaporous form are also suitable.
[0056] In one preferred embodiment two deposition precursors are
selected, a first deposition precursor where M is hafnium and a
second deposition precursor where M is silicon. Both the first and
second deposition precursor have the same ligands (L) to avoid
ligand exchange from taking place when the first and second
deposition precursor are mixed. Suitable ligands include, but not
limited to, dimethylamine, diethylamine, diethyl methyl amine or
tert-butoxide.
[0057] The hafnium source may comprise any one or combination of
hafnium dialkyl amides, hafnium alkoxides, hafnium dieketonates,
hafnium chloride (HfCl4), tetrakis(ethylmethylamino) hafnium
(TEMA-Hf), and the like. The silicon source may comprise any one or
combination of aminosilane, silicon alkoxides, silicon dialkyl
amides, silane, silicon chlorides, tetramethyldisiloxane (TMDSO),
tetrakis(ethylmethylamino) silicon (TEMA-Si), and the like. In one
preferred embodiment, the liquid precursors 124, 126, are comprised
of TEMA-Hf and TEMASi, respectively.
[0058] Deposition precursors are typically vaporized with a
vaporizer. Each vaporizer holds a single deposition precursor. Each
vaporizer is connected to a mass flow controller and a heating
mechanism. As described above according to one embodiment of the
present invention, a compositional gradient of one or more of the
chemical components in the deposited film is provided. In one
example, selective control of the composition is achieved by
controlling the amount of precursor that is vaporized. The amount
of precursor vaporized is generally controlled by adjusting the gas
flow controller and/or the temperature unit which heats the
vaporized in order to vaporize a desired concentration of the
selected precursor(s). Additionally or alternatively, a dilution
gas may be conveyed into the injector 114 or manifold 104 (not
shown) and the flow rate of the dilution gas may be selectively
controlled to dilute the amount of deposition precursor conveyed to
the chamber 102.
[0059] The vaporizer may be comprised of a bubbler that vaporizes
the deposition precursor comprising at least one deposition metal.
When the vaporizer is a blubber, pressurized gas such as a carrier
gas is bubbled into the deposition precursor reservoir 116, 118.
Useful carrier gases include nitrogen, argon, or helium gas. The
pressurized gas dilutes and carries the deposition precursors into
their respective deposition precursor conduits 106, 108, and
facilitates mixing of the deposition precursors. Optionally, to
provide a compositional gradient in the film the concentration of
one or more of the deposition precursors can be operable controlled
by varying the temperature of the bubbler to selective increase or
decrease the amount of deposition precursor vaporized. Temperature
control can be conducted independently or in tandem with control of
the mass flow controller and/or with the flow rate of the carrier
gas. Thus, each of the various control mechanism can be used
independently, or in a variety of combinations.
[0060] In other embodiments, due to the nature of the deposition
precursors, the deposition precursors can be volatilized in
reservoir 107, 109 by photolysis or enzymatic or chemical
catalysis.
[0061] Referring again to FIG. 1, after the deposition precursors
124, 126 are vaporized, the deposition precursors 124, 126 are
conveyed into manifold 104 through deposition precursor conduits
106, 108. The deposition precursor conduits 106, 108 can be of any
shape, size, and length. The conduits 106, 108 can be fabricated
from metal, plastics, polymers, or alloys. Typically, the conduits
are made of the same material as the manifold 104. Similar to the
manifold 104, the conduits 106, 108 can be insulated or heated to
facilitate vaporization. Optionally, the conduits 106, 108 and the
manifold 104 contain a sampling region for measuring the vapor
concentration and composition spectroscopically or
spectrometrically.
[0062] Mixing of the precursors can be facilitated by gravity or
pressurized gas. Mixing can also be achieved by physical means such
as a plunger to forcibly inject the precursors 124, 126 into
manifold 104 through conduits 106, 108, where precursors 124, 126
are permitted to mix into a homogeneous deposition mixture. In some
embodiments, the conduits 106, 108 converge and terminate at
T-junction 130 in manifold 104, where precursors 124, 126 mix prior
to delivery into process chamber 102.
[0063] Alternatively, conducts 106, 108 can converge and convey the
respective precursors directly into a mixing region or cavity near
or inlet to the chamber 102. In some embodiments, a filter can be
inserted or attached to the manifold 104 to remove unwanted or
isolate particular impurities and gases.
[0064] Optionally, referring back to the manifold 104 and conduits
106, 108, a heating or cooling element internally embedded or
externally located can be used to regulate mixing and minimize
particulate and impurity formation in the films.
[0065] The manifold 104 may take many forms suitable for mixing of
the precursors prior to conveying the precursors to the chamber
102. The manifold 104 may be a single conduit coupled to the
vaporizers via a junction, such as T-junction 130. The manifold 104
may include a cavity or reservoir to provide some residence time
for the precursors to mix. In an alternative embodiment the
manifold may be eliminated altogether, and the deposition
precursors are conveyed directly to the gas inlet 114 and mixed in
the gas inlet 114 (such as when the gas inlet is comprised of an
injector) as they are conveyed into the chamber 102.
[0066] Still referring to FIG. 1, once the precursors 124, 126 have
been vaporized, the deposition precursors 124, 126 are conveyed to
the chamber 102 via one or more gases inlets 114. The gas inlet may
take a variety of forms for delivery of gases to the chamber. In
one embodiment, the gas inlet is comprised of an injector, such as
a showerhead. It is also within the scope of the invention to
incorporate a showerhead that utilizes a plurality of injectors
adjustable in the process chamber 102 to provide desirable films.
While the illustrative embodiment shows a single wafer chamber
having one gas inlet 114, the present invention may be employed
with a batch processing chamber, or with a mini-batch chamber. In a
batch or mini-batch chamber, a plurality of gas inlets are employed
and the gases are typically conveyed over each substrate in a
parallel or cross-flow manner. Examples of a mini-batch chamber are
described in PCT patent application serial no. PCT/US03/21575
entitled Thermal Processing System and Configurable Vertical
Chamber, the disclosure of which is incorporated by reference
herein.
[0067] A layer of the deposition mixture, comprising precursors
124, 126, is deposited on substrate 112. Suitable substrates
include metal, metal alloy, glass, polymeric, plastic, organic or
inorganic work pieces. Depending on the mode of deposition, a
monolayer or monolayers of the deposition mixture will form on
substrate 112. The preferred method for deposition is Atomic Layer
Deposition. However, the system and method of the present invention
may be employed with other deposition techniques.
[0068] Referring again to FIG. 1, following deposition of the
deposition mixture, excess mixture is purged out of the system
through an exhaust port connected to a vacuum pump that controls
the system pressure, gas flow and insures rapid purging of the
process chamber 102 after each deposition process. The wafer
support 110 is used to support and heat the substrate during a
deposition or annealing step. The wafer support typically contains
heating and cooling elements formed therein. An external heater
(not shown) may also be used to control the temperature of the
process chamber. Preferably, the wafer support 110 is a vacuum or
electrostatic chuck.
[0069] Process chamber 102 has an inlet 103 switchably and
sequentially capable of supplying other gases used in the process
or in cleaning of the chamber. Reactant gases may be conveyed into
the chamber via inlet 103. Suitable reactant gases include
oxidizing gas, reducing gas, nitridating gas, or mixtures thereof.
Other gases which may be conveyed through inlet 103 include carrier
or inert gas, or mixtures thereof.
[0070] In one preferred embodiment, vaporized deposition precursors
are mixed in a manifold prior to introduction into the reaction
chamber in order to provide a more uniform film and to permit
maximum control of the composition of the film. However, it is
possible to separately convey each vaporized precursor to a gas
inlet, such as an injector and the like, which mixes the gases as
they are injected into the chamber, thus eliminating the need for a
separate manifold. A variety of mechanical embodiments are suitable
in light of the teaching of the present invention, and the present
invention is not limited to any one mechanical configuration. The
teaching of the present invention provides that at least some
mixing of the various different precursors takes place such that a
mixture of precursors having different chemical components is
present in the process chamber to form a film having multiple
components in one mono-layer.
[0071] A reactant gas may be introduced into the process chamber
102 through inlet 103, to treat and/or react with the monolayer
comprising the deposition mixture on the surface of the substrate
112. Reactant gases can be supplied sequentially or simultaneously
mixed with the deposition precursors in the gas inlet 114 or
directly into the process chamber 102.
[0072] A variety of reactant gases may be used depending on the
application. If the reactant gas is an oxidizing gas, the monolayer
is oxidized. If the reactant gas is a reducing gas, the monolayer
is reduced. Similarly, if the reactant gas is a nitridating gas,
the monolayer is nitridated. Suitable oxidizing gases include
ozone, oxygen, singlet oxygen, triplet oxygen, water, peroxides,
air, nitrous oxide, nitric oxide, H.sub.2O.sub.2, and mixtures
thereof. Suitable reducing gases include hydrogen. Suitable
nitridating gases include ammonia, deuterated ammonia,
.sup.15N-ammonia, hydrazine, alkyl hydrazines, nitrogen dioxide,
nitrous oxide, nitrogen radical, nitric oxide, N-oxides, amides,
amines, or mixtures thereof. In another embodiment, after the
deposition precursor has been deposited on substrate 112, substrate
112 can be transferred in vacuum to a second processing unit
capable of nitridating, oxidizing, reducing, or annealing the
monolayer on substrate 112.
[0073] In one example, to form a multi-component film comprising
HfSiN by ALD, a hafnium and silicon deposition precursors (for
example: TEMA-Hf and TEMA-Si, respectively) are vaporized, mixed
and conveyed (also referred to as "pulsed) to the process chamber
together, along with a nitrogen containing source such as
NH.sub.3to form HfSiN. The process may be carried out where the Hf
and Si deposition precursors are mixed together and pulsed into the
process chamber, then purged. The nitrogen source gas (such as
NH.sub.3) is pulsed and purged. These steps form one ALD cycle to
form the HfSiN film. In another embodiment, a further pulse and
purge step is performed with an oxidizing agent, such as ozone, in
one ALD cycle to form a HfSiON film.
[0074] In one example the ALD process is carried out at a process
temperature in the range of approximately 25 to 800.degree. C.,
more usually in the range of approximately 50 to 600.degree. C.,
and most usually in the range of approximately 100 to 500.degree.
C. The pressure in the process chamber is in the range of
approximately 0.001 mTorr to 600 Torr, more usually in the range of
approximately 0.01 mTorr to 100 Torr, and most usually in the range
of approximately 0.1 mTorr to 10 Torr. This pressure range covers
both the pulse and purge steps. The total inert gas flow rate in
the process chamber, including the carrier gas in the bubblers when
used, is generally in the range of approximately 0 to 20,000 sccm,
and more usually in the range of approximately 0 to 5,000 sccm.
[0075] Optionally, after the deposition precursor has been
deposited on substrate 112, substrate 112 can be transferred in
vacuo to a second processing unit capable of nitridating,
oxidizing, reducing, or annealing the monolayer on substrate
112.
[0076] FIG. 2 illustrates a cross-sectional view of a multi-layered
gate dielectric of the present invention. The first layer 200 is
selected to promote desired properties of high mobility (faster
transistor speed) and a stable interface against substrate 112.
Suitably, the first layer is a metal silicate or oxide having a
high dielectric constant. Preferably, the first layer is a
silicon-rich metal silicate. The silicon component in metal
silicates of the first layer reduces the formation of interfacial
defects by mitigating the incompatibility between pure metals or
metal oxides and the interfacial silicon dioxide residue on
substrate 112. The metal component in the metal silicate serves to
enhance the dielectric properties of the first layer. Suitable
metal, metal alloy or mix metal oxides, nitrides, silicates or
oxynitrides of the present invention include, but not limited to,
Ti, Zr, Hf, Ta, W, Mo, Ni, Si, Cr, Y, La, C, Nb, Zn, Fe, Cu, Al,
Sn, Ce, Pr, Sm, Eu, Th, Dy, Ho, Er, Tm, Yb, Lu, Ga, In, Ru, Mn, Sr,
Ba, Ca, V, Co, Os, Rh, Ir, Pd, Pt, Bi, Sn, Pb, Tl, Ge or mixtures
thereof.
[0077] One embodiment of the method of the present invention is
illustrated in the flowchart of FIG. 3. This example is shown for
illustration purposes only and is not meant to limit the invention
in any way. In the exemplary embodiment, a first precursor
vaporizer is provided having a first precursor comprising Hf (Step
150). A second precursor vaporizer having a second precursor
comprising Si is also provided (Step 152). The substrate or wafer
is positioned on the chuck in the reaction chamber (Step 154), the
process chamber is evacuated (Step 156), and the substrate heated
to a predetermined processing temperature (Step 158). As noted
above the process temperature is preferably from approximately 50
to 800.degree. C., and more preferably from approximately 100 to
500.degree. C. The first and second precursors are vaporized by
bubbling a gas through the reservoirs to form first and second
vaporized precursors (Step 160), mixed (Step 162), and flowed to
the reaction chamber (Step 164). The mixed first and second
vaporized precursors are directed on to the substrate through the
gas inlet such as showerhead or injection nozzle (Step 166).
[0078] The present invention further provides a multi-component
film or layer having a composition gradient as illustrated in FIG.
2. Referring to FIGS. 1 and 2 deposition of first layer 200 onto
silicon substrate 112 takes place in process chamber 102. In one
example, a film of HfSiO is formed wherein hafnium is vaporized in
vaporizer 107, and silicon is vaporized in vaporizer 109. Hafnium
and silicon deposition precursor vapors are swept into manifold 104
by a carrier gas. Within the manifold, the deposition precursor
vapors are mixed and delivered to gas inlet 114 as a deposition
mixture. Gas inlet 114 conveys the disposition mixture to the
process chamber 102 and the deposition mixture contacts the surface
of a substrate 112 and is absorbed on the surface to form a
monolayer of the deposition mixture onto substrate 112. After the
process chamber 102 is purged with an inert gas or evacuated under
vacuum, ozone gas is sequentially pulsed into process chamber 102
through inlet 103. The reactant gas saturates the monolayer on
substrate 12 forming an atomic layer comprising hafnium, silicon
and oxygen, where the silicon content is higher than hafnium.
[0079] FIG. 4 illustrates that by varying the flow of deposition
precursors 124 and 126, the concentration of silicon relative to
hafnium can be tailored to yield multi-component films. FIG. 5
shows that changes in silicon or hafnium concentration are, for the
most part, governed by the formula Hf.sub.xSi.sub.1-xO.sub.2, where
x=0-1.
[0080] XPS studies on Hf.sub.xSi.sub.1-xO.sub.2 films shed light on
the bonding arrangement of atoms in the films. FIG. 6a represents
the XPS spectrum of hafnium in the film. Based on the intensity of
the absorption bands and the magnitude of the bonding energies,
hafnium is predominantly found in a silicate form. Very little
amount of impurities such as HfO.sub.2 is seen in the spectrum. Now
referring to FIG. 6b, the XPS spectrum of silicon reveals that
silicon also exists predominantly as a silicate with no or very
little SiO.sub.2 formation. The XPS results highlight the
advantages of the present invention. That is, the formation of
homogeneous hafnium silicate films with no or minimal patches of
HfO.sub.2 or SiO.sub.2.
[0081] Now referring to FIG. 7, refractive indices of dielectric
films of the present invention decrease with increasing silicon
content. FIG. 7 shows that heating the films in a N.sub.2
atmosphere at 900.degree. C. causes no thermal alterations.
[0082] FIG. 8 shows that the rate of deposition is temperature
dependent. The rate of linear growth of Hf.sub.xSi.sub.1-xO.sub.2
increases with temperature. However, above 400.degree. C., the
deposition rate increases substantially as the atomic layer
deposition (ALD) process adopts a chemical vapor deposition (CVD)
mechanism. Cross-sectional Transmission Electron Microscopy (TEM)
images of Hf.sub.0.58Si.sub.0.42O.sub.2 film deposited at
400.degree. C. on HF-last silicon substrates, at various thick
nesses, show similar interfacial layer thickness measuring
approximately 1 nm. Comparing FIGS. 9a, 9b and 9c, each having a
dielectric thickness of 2.3 nm, 4.3 nm and 6.5 nm, respectively,
the interfacial thickness is independent of the dielectric
thickness. This suggests that, when ozone is used as the oxidizing
reactant in an ALD process, the oxidation at the interface may take
place during the initial stages of film fabrication.
[0083] Although heating at elevated temperatures does not alter the
amorphous state of the dielectric, annealing decreases the
interfacial oxide layer. FIG. 10 shows a TEM image of the
Hf.sub.0.58Si.sub.0.42O.sub- .2 film after annealing. Comparing the
thickness of the interfacial oxide layer to FIG. 9, annealing seems
to reduce the interfacial layer by 0.3 nm without changing either
the capacitance-voltage (CV) or current-voltage (IV). FIG. 11 shows
that the films are electrically stable to annealing. Neither
capacitance-equivalent thickness (CET) nor the low leakage current
densities were greatly affected by the annealing step.
[0084] Stress hysteresis measurement for a 50 nm thick
Hf.sub.0.34Si.sub.066O.sub.2 film, during an anneal to 900.degree.
C., was monitored. As shown in FIG. 12, the consistent slope during
heat-up indicates a fairly stable difference in thermal expansion
between the deposited Hf.sub.0.34Si.sub.066O.sub.2 film and the
silicon substrate. At approximately 700.degree. C., the stress
becomes more tensile, indicating a change in morphology to a
microcrystalline state. Relative to an HfO.sub.2 film, deposited by
ALD from TEMAHf and O.sub.3 at 300.degree. C., which possesses a
stress increase at approximately 450.degree. C. (not shown), the
increase in film stress transition temperature in
Hf.sub.xSi.sub.1-xO.sub.2 is attributable to an increase in the
silicon content. Thus, an increase in silicon content increases the
temperature at which films crystallize.
[0085] Suitable source of hafnium include hafnium dialkyl amides,
hafnium alkoxides, hafnium diketonates or hafnium halides. Suitable
sources of silicon include silicon halides, silicon dialkyl amides
or amines, silicon alkoxides, silanes, disilanes, siloxanes,
aminodisilane, and disilicon halides. Typically, sources of hafnium
and silicon are selected having common ligands to prevent
complications arising from ligand exchange. Covalently bridged
mixed metals, as disclosed in PCT patent application serial number
PCT/US03/22236 entitled Molecular Layer Deposition Of Thin Films
With Mixed Components, incorporated herein by reference, as well as
non-covalently bonded mixed metals may be used as precursors for
deposition. Types of non-covalent bonds include hydrogen bonds,
dative bonds, metal-metal bonds, metal-.pi., metal-.pi.*, .pi.-.pi.
bonds, sigma-sigma bonds, ionic bonds, Van Der Waals interactions,
hydrophobic/hydrophilic interactions, polar bonds or dipole moment
interactions. Sources of inert gases include carrier gases such
argon, nitrogen, inert gases, or a mixture thereof.
[0086] Again referring to FIG. 2, a second layer 202 is deposited
on the first layer 200, wherein the second layer 202 has a greater
concentration of hafnium than silicon, i.e., hafnium>silicon.
The higher concentration of hafnium ensures that the overall
make-up of the dielectric behaves like a high k hafnium dielectric.
The presence of silicon in the second layer 202 creates a gradual
stoichiometric transition from first layer 200 so that there are no
abrupt compositional interfaces between the individual layers that
may cause electrical leakage and defects. Subsequent oxidation with
ozone affords second layer 202.
[0087] In various embodiments of the present invention, a third
layer 203 can optionally be deposited comprising primarily hafnium,
i.e., hafnium>>silicon, atop second layer 202 to form a stack
of dielectric layers having a compositional gradient. Oxidation
with an oxidizing reactant yields predominantly hafnium dioxide.
Utilizing this approach, a homogeneous film of any gradient,
thickness and composition can be fabricated with precision and
control.
[0088] In another aspect, third layer 203 may be nitridated with a
nitridating reactant. The inclusion of nitrogen blocks the
diffusion of impurities such as boron through the dielectric, and
enhances the long-term performance and reliability of the film.
[0089] In some embodiments, third layer 203 can be nitridated
thermally in the presence of ammonia gas as a post-deposition
annealing step. Whereas, in other embodiments, third layer 203 can
be nitridated using high energy nitrogen particles generated
remotely with respect to the process chamber 102. In accordance
with one aspect of the present invention, FIG. 13 shows an XPS
spectrum for an exemplary post-annealed film with ammonia. Relative
to a HfSiO reference also shown in FIG. 13, the presence of the
nitrogen peak near 400 eV indicates the incorporation of nitrogen
into the HfSiO layer. Measurements at various take-off angles (TOA)
detect the presence of HfSiON not only at the surface of the
dielectric, but as well as deep within the film.
[0090] Optionally, if desired, instead of relying on heat to form
and anneal the nitride layer, nitridation can be facilitated by
light or any combination of light, heat and chemical initiators.
For example, in certain embodiments, direct plasma, remote plasma,
downstream plasma, ultraviolet photon energy, or a combination
thereof, can be used to facilitate nitridation. Activation energy
sources include plasma, light, laser, radical, and microwave energy
sources, and mixtures thereof.
[0091] As previously mentioned in a separate embodiment, suitable
nitrogen sources include ammonia, deuterated ammonia, .sup.15N
enriched ammonia, amines, amides, nitrogen gas, hydrazines, alky
hydrazines, nitrous oxide, nitric oxide, nitrogen radicals,
N-oxides, or a mixture thereof.
[0092] In yet another aspect of the present invention, although
related to the nitridation of films, an ambient method of
nitridating dielectrics is provided. FIG. 14 shows that the rate of
HfO.sub.2 deposition, arising from the reaction between hafnium
dialkyl amide precursors and ozone, increases, surprisingly, with a
decrease in reaction temperature. In view of ozone's reactivity
toward hafnium dialky amide, HfSiOx 300 was deposited onto
substrate precursor 112 as shown in FIG. 14 by vaporizing hafnium
and silicon in vaporizers 107 and 109, respectively, of FIG. 1.
Ozone is supplied through inlet 103 into the process chamber 102
housing substrate 112. Oxidation occurs rapidly at relatively low
temperatures as in FIG. 16a to afford hafnium oxide 302. To protect
layer 302 from boron diffusion from the gate electrode, an
oxynitride layer 304 is desirable atop metal oxide 302.
[0093] There are two methods for depositing oxynitride layer 304.
In the first method, as depicted in FIG. 16a, the deposition
precursor or precursors 124, 126 are vaporized and injected into
process chamber 102 forming a monolayer of deposition mixture on
substrate 112.
[0094] Now referring to FIG. 16a, despite a low temperature
oxidation that affords oxide 302, the subsequently thermal
oxynitridation anneal at 800.degree. C. with ammonia is tolerable,
yet unfavorable from a process stand point. Structurally, such high
annealing temperatures pose a greater concern. That is, the
crystallization of oxide layer 302, leading to possible intrinsic
defects deep within or at the grain boundaries of oxide 302.
[0095] In the preferred embodiment of the present invention, the
second method for depositing oxynitride is shown in FIG. 16b. The
method in FIG. 16b, relative to the method in FIG. 16a, is a more
economical pathway to oxynitride 304. Since ozone reacts readily
with metal dialkyl amides, a deposition mixture is first deposited
onto substrate 112 and treated in-situ with ammonia sequentially.
Following the formation of nitride 303 at relatively low
temperatures, oxidation with ozone drives the reaction to
completion affording oxynitride 304.
[0096] In some embodiments of the present invention, deuterated
ammonia or .sup.15N-ammonia is preferred.
[0097] FIG. 17 shows the compositional profile below the surface of
oxynitride 304. Nitrogen concentration is greatest on the surface
of the film, but gradually decrease below the surface until the
HfO.sub.2 layer is reached. With further penetration into the film,
the concentration of HfO.sub.2 302 decreases giving away to
HfSiO.sub.x 300, until the interfacial layer of the silicon
substrate 112 is reached.
[0098] In accordance with the present invention, numerous layers of
HfSiON having different film thickness and nitrogen or oxygen
concentration can be deposited. While specific examples describing
the formation of SiO.sub.2, HfO.sub.2, HfSiO.sub.x, HfN, SiN, SiON
and HfSiON are shown herein, it will be apparent to those of
ordinary skill in the art that the inventive method and ALD system
may be employed to generate any thickness, composition, or types of
thin films comprising metal, metal alloys or mix metals oxides,
silicates, nitrides, oxynitrides, or combinations thereof.
[0099] The foregoing description of specific embodiments of the
invention have been presented for the purpose of illustration and
description. They are not intended to be exhaustive or to limit the
invention to the precise forms disclosed, and obviously many
modifications, embodiments, and variations are possible in lights
of the above teaching. It is intended that the scope of the
invention be defined by the Claims appended hereto and their
equivalents.
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