U.S. patent application number 11/217507 was filed with the patent office on 2006-03-09 for systems and methods of forming tantalum silicide layers.
This patent application is currently assigned to MICRON TECHNOLOGY, INC.. Invention is credited to Brian A. Vaartstra.
Application Number | 20060048711 11/217507 |
Document ID | / |
Family ID | 31976326 |
Filed Date | 2006-03-09 |
United States Patent
Application |
20060048711 |
Kind Code |
A1 |
Vaartstra; Brian A. |
March 9, 2006 |
Systems and methods of forming tantalum silicide layers
Abstract
A method of forming (and apparatus for forming) tantalum
silicide layers (including tantalum silicon nitride layers), which
are typically useful as diffusion barrier layers, on a substrate by
using a vapor deposition process with a tantalum halide precursor
compound, a silicon precursor compound, and an optional nitrogen
precursor compound.
Inventors: |
Vaartstra; Brian A.; (Nampa,
ID) |
Correspondence
Address: |
MUETING, RAASCH & GEBHARDT, P.A.
P.O. BOX 581415
MINNEAPOLIS
MN
55458
US
|
Assignee: |
MICRON TECHNOLOGY, INC.
Boise
ID
|
Family ID: |
31976326 |
Appl. No.: |
11/217507 |
Filed: |
September 1, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10229813 |
Aug 28, 2002 |
|
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11217507 |
Sep 1, 2005 |
|
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Current U.S.
Class: |
118/726 ;
118/723E; 118/724; 257/E21.171 |
Current CPC
Class: |
H01L 28/57 20130101;
H01L 21/28562 20130101; C23C 16/45553 20130101; C23C 16/42
20130101; C23C 16/30 20130101; H01L 21/76843 20130101; C23C 16/08
20130101; H01L 21/28556 20130101; H01L 21/7687 20130101; C23C
16/45523 20130101 |
Class at
Publication: |
118/726 ;
118/724; 118/723.00E |
International
Class: |
C23C 16/00 20060101
C23C016/00 |
Claims
1-46. (canceled)
47. A vapor deposition apparatus comprising: a vapor deposition
chamber having a substrate positioned therein; and one or more
vessels comprising one or more tantalum precursor compounds of the
formula TaY.sub.5 (Formula I), wherein each Y is independently a
halogen atom; and one or more vessels comprising one or more
silicon precursor compounds.
48. (canceled)
49. An atomic layer deposition system comprising: a vapor
deposition chamber having positioned therein a substrate comprising
a silicon-containing surface; one or more vessels comprising one or
more tantalum precursor compounds of the formula TaY.sub.5 (Formula
I), wherein each Y is independently a halogen atom; and one or more
vessels comprising one or more silicon precursor compounds, with
the proviso that the system does not include one or more nitrogen
precursor compounds.
50. The system of claim 49 wherein the system can direct vapors of
the one or more tantalum precursor compounds and vapors of the one
or more silicon precursor compounds to the substrate using an
atomic layer deposition process comprising a plurality of
deposition cycles.
51. The system of claim 49 wherein each Y is a fluorine atom.
52. The system of claim 49 wherein the silicon precursor compound
is silane or disilane.
53. The system of claim 49 wherein the silicon precursor compound
is a halogenated silane or an organic silane.
54. The system of claim 53 wherein the silicon precursor compound
is a halogenated silane of the formula SiH.sub.rCl.sub.s wherein
r=1-4 and s=4-r.
55. The system of claim 53 wherein the silicon precursor compound
is an organic silane of the formula SiH.sub.pR.sub.q wherein p=1-4,
q=4-p, and each R is independently an organic group.
56. The system of claim 49 wherein the temperature of the substrate
is about 25.degree. C. to about 400.degree. C.
57. The system of claim 49 further comprising providing one or more
vessels comprising one or more metal-containing precursor compounds
having a formula different than Formula I.
58. An atomic layer deposition system comprising: a vapor
deposition chamber having positioned therein a semiconductor
substrate or substrate assembly comprising a silicon-containing
surface; one or more vessels comprising one or more tantalum
precursor compounds of the formula TaY.sub.5 (Formula I), wherein
each Y is independently a halogen atom; and one or more vessels
comprising one or more silicon precursor compounds, with the
proviso that the system does not include one or more nitrogen
precursor compounds.
59. The system of claim 58 wherein the system can direct vapors of
the one or more tantalum precursor compounds and vapors of the one
or more silicon precursor compounds to the semiconductor substrate
or substrate assembly using an atomic layer deposition process
comprising a plurality of deposition cycles.
60. The system of claim 58 wherein the semiconductor substrate or
substrate assembly is a silicon wafer.
61. The system of claim 58 wherein the semiconductor substrate or
substrate assembly is in a deposition chamber having a pressure of
about 10.sup.-4 torr to about 1 torr.
62. The system of claim 58 wherein the system can alternately
introduce vapors of the one or more tantalum precursor compounds
and vapors of the one or more silicon precursor compounds during
each deposition cycle.
63. The system of claim 58 further comprising providing one or more
vessels comprising one or more metal-containing precursor compounds
having a formula different than Formula I.
Description
[0001] This is a divisional of U.S. patent application Ser. No.
10/229,813, filed Aug. 28, 2002, (pending), which is incorporated
herein by reference.
FIELD OF THE INVENTION
[0002] This invention relates to methods of forming tantalum layers
containing silicon (suicide layers) and optionally nitrogen
(silicon-nitride layers) on substrates using a vapor deposition
process. The formed tantalum-containing layers are particularly
useful as diffusion barriers for polysilicon substrates to reduce
diffusion of oxygen, copper, or silicon.
BACKGROUND OF THE INVENTION
[0003] In very-large-scale integration (VLSI) technology, tantalum
suicide has been proposed to be useful in a variety of
applications. These include: policide gate metallization (i.e., the
use of tantalum silicide in combination with a doped
polycrystalline silicon (poly-Si) underlayer as a low resistive
gate metallization layer); silicide gate (i.e., the use of tantalum
silicide as a directly deposited layer on a gate oxide to reduce
sheet resistance); source-drain silicidation (i.e., the use of
tantalum silicide in the silicidation of contacts thereby providing
in low resistive contacts); and diffusion barrier (i.e., the use of
tantalum silicide a diffusion barrier between an Al--Si--Ti layer
and silicon thereby providing reliable and low resistive contacts
to n+ and p+ Si). Tantalum silicon nitride (Ta--Si--N) has also
been shown to form a useful conductive barrier layer between
silicon substrates and copper interconnects to reduce copper
diffusion.
[0004] Lee et al., "Structural and chemical stability of Ta--Si--N
thin film between Si and Cu," Thin Solid Films, 320:141-146 (1998)
describe amorphous, ultra-thin (i.e., less than 100 .ANG.)
tantalum-silicon-nitrogen barrier films between silicon and copper
interconnection materials used in integrated circuits. These
barrier films suppress the diffusion of copper into silicon, thus
improving device reliability. Barrier films having compositions
ranging from TaA.sub.0.43Si.sub.0.04N.sub.0.53 to
Ta.sub.0.60Si.sub.0.11N.sub.0.29 were deposited on silicon by
reactive sputtering from Ta and Si targets in an Ar/N.sub.2
discharge, followed by sputter-depositing copper films.
[0005] Methods for using physical vapor deposition (PVD) methods,
such as reactive sputtering, to form Ta--Si--N barrier layers are
known. Hara et al., "Barrier Properties for Oxygen Diffusion in a
TaSiN Layer," Jpn J. Appl.-Phys., 36(7B), L893 (1997) describe
noncrystalline, low resistivity Ta--Si--N layers that acts as a
barrier to oxygen diffusion during high temperature annealing at
650.degree. C. in the presence of O.sub.2. The Ta--Si--N layers are
formed by using radio-frequency reactive sputtering with pure Ta
and Si targets on a 100 nm thick polysilicon layer. Layers having
relatively low silicon content, such as
Ta.sub.0.50Si.sub.0.16N.sub.0.34 are stated to have a desirable
combination of good diffusion barrier resistance along with low
sheet resistance. These Ta--Si--N barrier layers have improved peel
resistance over Ta--N barrier layers during annealing
conditions.
[0006] However, when PVD methods are used, the stoichiometric
composition of the formed metal silicon nitride barrier layers such
as Ta--Si--N can be non-uniform across the substrate surface due to
different sputter yields of Ta, Si, and N. Due to the resulting
poor layer conformality, defects such as pinholes often occur in
such layers creating pathways to diffusion. As a result, the
effectiveness of a physically deposited diffusion barrier layer is
dependent on the layer being sufficiently thick.
[0007] Vapor deposition processes such as chemical vapor deposition
(CVD) and atomic layer deposition (ALD) processes are preferable to
PVD processes in order to achieve the most efficient and uniform
barrier layer coverage of substrate surfaces. There remains a need
for a vapor deposition process to form tantalum silicides and
tantalum silicon nitride barrier layers on substrates, such as
semiconductor substrates or substrate assemblies.
SUMMARY OF THE INVENTION
[0008] This invention is directed to methods of using vapor
deposition processes to deposit tantalum silicide layers (including
tantalum silicon nitride layers) on substrates. The process
involves combining one or more tantalum halide precursor compounds
(preferably, TaF.sub.5), one or more silicon precursor compounds,
and optionally one or more nitrogen sources such as ammonia (as
nitrogen precursor compound(s)).
[0009] In one embodiment, the present invention provides a method
of forming a layer on a substrate (preferably, in a process of
manufacturing a semiconductor structure). The method includes:
providing a substrate (preferably a semiconductor substrate or
substrate assembly such as a silicon wafer); providing a vapor that
includes one or more tantalum precursor compounds of the formula
TaY.sub.5 (Formula I), wherein each Y is independently a halogen
atom (preferably, F, Cl, I, or combinations thereof, and more
preferably, F); providing a vapor that includes one or more silicon
precursor compounds; and directing the vapors that include the one
or more tantalum precursor compounds and the one or more silicon
precursor compound to the substrate to form a tantalum silicide
layer on one or more surfaces of the substrate. The resultant
silicide layer (or silicon nitride layer) is typically suitable for
use as a diffusion barrier layer, which is particularly
advantageous when the substrate includes a silicon-containing
surface.
[0010] The present invention also provides a method of
manufacturing a memory device. The method includes: providing a
substrate (preferably a semiconductor substrate or substrate
assembly) that includes a silicon-containing surface; providing a
vapor that includes one or more tantalum precursor compounds of the
formula TaY.sub.5 (Formula I), wherein each Y is independently a
halogen atom; directing the vapor that includes the one or more
precursor compounds of the Formula I to the substrate and allowing
the one or more compounds to chemisorb on the silicon-containing
surface; providing a vapor that includes one or more silicon
precursor compounds; directing the vapor that includes the one or
more silicon precursor compounds to the substrate with the
chemisorbed compounds thereon to form a tantalum silicide barrier
layer on the silicon-containing surface; providing a first
electrode on the barrier layer; providing a high dielectric
material over at least a portion of the first electrode; and
providing a second electrode over the high dielectric material.
[0011] Preferred methods of the present invention also include
steps of providing a vapor that includes one or more nitrogen
precursor compounds and directing the vaporized nitrogen precursor
compounds to the substrate to form a tantalum silicon nitride
layer. Optionally, in certain embodiments, the methods can provide
a vapor that includes one or more metal-containing precursor
compounds of a different formula from Formula I and direct this
vapor to the substrate.
[0012] The present invention also provides a vapor deposition
apparatus that includes: a vapor deposition chamber having a
substrate positioned therein; and one or more vessels that include
one or more tantalum precursor compounds of the formula TaY.sub.n
(Formula I), wherein each Y is independently a halogen atom; and
one or more vessels that include one or more silicon precursor
compounds. Optionally, the apparatus can include one or more
vessels with one or more nitrogen precursor compounds therein.
[0013] The methods of the present invention can utilize a chemical
vapor deposition (CVD) process, which can be pulsed, or an atomic
layer deposition (ALD) process (a self-limiting vapor deposition
process that includes a plurality of deposition cycles, typically
with purging between the cycles). Preferably, the methods of the
present invention use ALD. In one embodiment of an ALD process, the
tantalum silicide layer is formed by alternately introducing the
one or more vaporized precursor compounds and one or more vaporized
silicon precursor compounds into a deposition chamber during each
deposition cycle.
[0014] "Substrate" as used herein refers to any base material or
construction upon which a metal-containing layer can be deposited.
The term "substrate" is meant to include semiconductor substrates
and also include non-semiconductor substrates such as films, molded
articles, fibers, wires, glass, ceramics, machined metal parts,
etc.
[0015] "Semiconductor substrate" or "substrate assembly" as used
herein refers to a semiconductor substrate such as a metal
electrode, base semiconductor layer or a semiconductor substrate
having one or more layers, structures, or regions formed thereon. A
base semiconductor layer is typically the lowest layer of silicon
material on a wafer or a silicon layer deposited on another
material, such as silicon on sapphire. When reference is made to a
substrate assembly, various process steps may have been previously
used to form or define regions, junctions, various structures or
features, and openings such as capacitor plates or barriers for
capacitors.
[0016] "Layer" as used herein refers to any metal-containing layer
that can be formed on a substrate from the precursor compounds of
this invention using a vapor deposition process. The term "layer"
is meant to include layers specific to the semiconductor industry,
such as "barrier layer," "dielectric layer," and "conductive
layer." (The term "layer" is synonymous with the term "film"
frequently used in the semiconductor industry.) The term "layer" is
also meant to include layers found in technology outside of
semiconductor technology, such as coatings on glass.
[0017] "Barrier layer" as used herein refers to a conductive,
interfacial layer that can reduce diffusion of ambient oxygen
through a dielectric layer into a semiconductor substrate
(typically a polysilicon substrate) or can reduce diffusion of one
layer into another, such as a copper conductive layer into a
semiconductor substrate (typically a polysilicon substrate). For
this invention, the barrier layer is a tantalum silicide or
tantalum silicon nitride layer.
[0018] "Precursor compound" as used herein refers to tantalum
precursor compounds, nitrogen precursor compounds, silicon
precursor compounds, and other metal-containing precursor
compounds, for example. A suitable precursor compound is one that
is capable of forming, either alone or with other precursor
compounds, a tantalum-containing layer on a substrate using a vapor
deposition process. The resulting tantalum-containing layers also
typically include silicon and optionally nitrogen. Such layers are
often useful as diffusion barrier layers (i.e., barrier
layers).
[0019] "Deposition process" and "vapor deposition process" as used
herein refer to a process in which a metal-containing layer is
formed on one or more surfaces of a substrate (e.g., a doped
polysilicon wafer) from vaporized precursor compound(s).
Specifically, one or more metal precursor (i.e., metal-containing
precursor) compounds are vaporized and directed to one or more
surfaces of a heated substrate (e.g., semiconductor substrate or
substrate assembly) placed in a deposition chamber. These precursor
compounds form (e.g., by reacting or decomposing) a non-volatile,
thin, uniform, metal-containing layer on the surface(s) of the
substrate. For the purposes of this invention, the term "vapor
deposition process" is meant to include both chemical vapor
deposition processes (including pulsed chemical vapor deposition
processes) and atomic layer deposition processes.
[0020] "Chemical vapor deposition" (CVD) as used herein refers to a
vapor deposition process wherein the desired layer is deposited on
the substrate from vaporized metal precursor compounds and any
reaction gases used within a deposition chamber with no effort made
to separate the reaction components. In contrast to a "simple" CVD
process that involves the substantial simultaneous use of the
precursor compounds and any reaction gases, "pulsed" CVD
alternately pulses these materials into the deposition chamber, but
does not rigorously avoid intermixing of the precursor and reaction
gas streams, as is typically done in atomic layer deposition or ALD
(discussed in greater detail below).
[0021] "Atomic layer deposition" (ALD) as used herein refers to a
vapor deposition process in which numerous consecutive deposition
cycles are conducted in a deposition chamber. Typically, during
each cycle the metal precursor is chemisorbed to the substrate
surface; excess precursor is purged out; a subsequent precursor
and/or reaction gas is introduced to react with the chemisorbed
layer; and excess reaction gas (if used) and by-products are
removed. As compared to the one cycle chemical vapor deposition
(CVD) process, the longer duration multi-cycle ALD process allows
for improved control of layer thickness by self-limiting layer
growth and minimizing detrimental gas phase reactions by separation
of the reaction components. The term "atomic layer deposition" as
used herein is also meant to include the related terms "atomic
layer epitaxy" (ALE) (see U.S. Pat. No. 5,256,244 (Ackerman)),
molecular beam epitaxy (MBE), gas source MBE, organometallic MBE,
and chemical beam epitaxy when performed with alternating pulses of
precursor compound(s), reaction gas and purge (i.e., inert carrier)
gas.
[0022] "Chemisorption" as used herein refers to the chemical
adsorption of vaporized reactive precursor compounds on the surface
of a substrate. The adsorbed species are irreversibly bound to the
substrate surface as a result of relatively strong binding forces
characterized by high adsorption energies (>30 kcal/mol),
comparable in strength to ordinary chemical bonds. The chemisorbed
species are limited to the formation of a monolayer on the
substrate surface. (See "The Condensed Chemical Dictionary", 10th
edition, revised by G. G. Hawley, published by Van Nostrand
Reinhold Co., New York, 225 (1981)). The technique of ALD is based
on the principle of the formation of a saturated monolayer of
reactive precursor molecules by chemisorption. In ALD one or more
appropriate reactive precursor compounds are alternately introduced
(e.g., pulsed) into a deposition chamber and chemisorbed onto the
surfaces of a substrate. Each sequential introduction of a reactive
precursor compound is typically separated by an inert carrier gas
purge. Each precursor compound co-reaction adds a new atomic layer
to previously deposited layers to form a cumulative solid layer.
The cycle is repeated, typically for several hundred times, to
gradually form the desired layer thickness. It should be
understood, however, that ALD can use one precursor compound and
one reaction gas.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 shows a device structure including a tantalum
silicide diffusion barrier layer according to the present
invention.
[0024] FIG. 2 is a structure showing a high dielectric capacitor
including an electrode having a tantalum silicide diffusion barrier
layer according to the present invention.
[0025] FIG. 3 is a perspective view of a vapor deposition coating
system suitable for use in the method of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0026] The present invention provides methods of forming a
tantalum-containing layer on a substrate using a vapor deposition
process with one or more tantalum halide precursor compounds, one
or more silicon precursor compounds, and optionally one or more
nitrogen precursor compounds. For the present invention, the
tantalum-containing layer is a tantalum silicide layer, preferably,
a tantalum silicon nitride layer.
[0027] The layers of the present invention are preferably
conductive. That is, they preferably display an electrical
resistivity of no more than about 10 m.OMEGA.-cm. The layers of the
present invention are typically useful as barrier layers,
particularly in the manufacture of semiconductor interconnects. For
example, TaSi.sub.2 makes ohmic contact to silicon and is a good
barrier for tungsten, aluminum, and copper interconnects. The
silicide and ternary silicide-nitride are also being considered as
copper barriers, but also have possible application for high
dielectric constant barriers or electrodes. Other applications for
the layers of the present invention include polycide gate
metallization and gate electrodes. Composites containing TaSi.sub.2
are also of interest as wide bandpass optical elements.
[0028] The layers or films formed can be in the form of tantalum
silicide-containing films or tantalum silicon nitride-containing
films, wherein the layer includes tantalum silicide (i.e., tantalum
silicon) or tantalum silicon nitride optionally doped with other
metals. Thus, the term "tantalum silicon (nitride)" films or layers
encompass tantalum silicides (typically TaSi.sub.2), tantalum
silicon nitrides (typically Ta.sub.xSi.sub.yN.sub.z of all possible
proportions of Ta, Si, and N), as well as doped films or layers
thereof (e.g., mixed metal silicon (nitride)s). Such mixed metal
species can be formed using one or more metal-containing precursor
compounds of a formula different from Formula I, which can be
readily determined by one of skill in the art.
[0029] The substrate on which the metal-containing layer is formed
is preferably a semiconductor substrate or substrate assembly. Any
suitable semiconductor material is contemplated, such as for
example, conductively doped polysilicon (for this invention simply
referred to as "silicon"). A substrate assembly may also contain a
layer that includes platinum, iridium, rhodium, ruthenium,
ruthenium oxide, titanium nitride, tantalum nitride,
tantalum-silicon-nitride, silicon dioxide, aluminum, gallium
arsenide, glass, etc., and other existing or to-be-developed
materials used in semiconductor constructions, such as dynamic
random access memory (DRAM) devices and static random access memory
(SRAM) devices, for example. Preferred substrates include a
silicon-containing surface.
[0030] Substrates other than semiconductor substrates or substrate
assemblies can be used in methods of the present invention. These
include, for example, fibers, wires, etc. If the substrate is a
semiconductor substrate or substrate assembly, the layers can be
formed directly on the lowest semiconductor surface of the
substrate, or they can be formed on any of a variety of the layers
(i.e., surfaces) as in a patterned wafer, for example.
[0031] Metal precursor compounds (i.e., metal-containing precursor
compounds) useful in the practice of this invention are of the
formula TaY.sub.5 (Formula I) wherein each Y is independently a
halogen atom. More preferably, each Y is a fluorine atom. For
particularly preferred embodiments, the refractory metal precursor
compound is a tantalum precursor compound of the formula
TaF.sub.5.
[0032] Silicon precursor compounds useful in the practice of this
invention include silane (SiH.sub.4), disilane (Si.sub.2H.sub.6),
halogenated silanes (preferably chlorinated silanes of the formula
SiH.sub.rCl.sub.s wherein r=1-4 and s=4-r), and organic silanes of
the formula SiH.sub.pR.sub.q wherein p=1-4, q=4-p, and each R is
independently an organic group (preferably having up to six carbon
atoms, more preferably up to two carbon atoms, and most preferably,
being an organic moiety). Examples include silane (SiH.sub.4),
disilane (Si.sub.2H.sub.6), dichlorosilane (SiH.sub.2Cl.sub.2),
trichlorosilane (SiHCl.sub.3), and trimethylsilane
(SiH(CH.sub.3).sub.3).
[0033] Optional nitrogen precursor compounds useful in the practice
of this invention include ammonia (NH.sub.3), hydrazine
(N.sub.2H.sub.4), dimethyl hydrazine, as well as other nitrogen
sources such as organic amines, such as those disclosed in U.S.
patent application Ser. No. 10/229,743, filed on Aug. 28, 2002, and
the disilazanes disclosed in U.S. Pat. No. 6,794,284, issued on
Sep. 21, 2004.
[0034] As used herein, the term "organic group" is used for the
purpose of this invention to mean a hydrocarbon group that is
classified as an aliphatic group, cyclic group, or combination of
aliphatic and cyclic groups (e.g., alkaryl and aralkyl groups). In
the context of the present invention, suitable organic groups for
precursor compounds of this invention are those that do not
interfere with the formation of a metal-containing layer using
vapor deposition techniques. In the context of the present
invention, the term "aliphatic group" means a saturated or
unsaturated linear or branched hydrocarbon group. This term is used
to encompass alkyl, alkenyl, and alkynyl groups, for example. The
term "alkyl group" means a saturated linear or branched monovalent
hydrocarbon group including, for example, methyl, ethyl, n-propyl,
isopropyl, t-butyl, amyl, heptyl, 2-ethylhexyl, dodecyl, octadecyl,
and the like. The term "alkenyl group" means an unsaturated, linear
or branched monovalent hydrocarbon group with one or more
olefinically unsaturated groups (i.e., carbon-carbon double bonds),
such as a vinyl group. The term "alkynyl group" means an
unsaturated, linear or branched monovalent hydrocarbon group with
one or more carbon-carbon triple bonds. The term "cyclic group"
means a closed ring hydrocarbon group that is classified as an
alicyclic group, aromatic group, or heterocyclic group. The term
"alicyclic group" means a cyclic hydrocarbon group having
properties resembling those of aliphatic groups. The term "aromatic
group" or "aryl group" means a mono- or polynuclear aromatic
hydrocarbon group. The term "heterocyclic group" means a closed
ring hydrocarbon in which one or more of the atoms in the ring is
an element other than carbon (e.g., nitrogen, oxygen, sulfur,
etc.).
[0035] As a means of simplifying the discussion and the recitation
of certain terminology used throughout this application, the terms
"group" and "moiety" are used to differentiate between chemical
species that allow for substitution or that may be substituted and
those that do not so allow for substitution or may not be so
substituted. Thus, when the term "group" is used to describe a
chemical substituent, the described chemical material includes the
unsubstituted group and that group with nonperoxidic O, N, Si, F,
or S atoms, for example, in the chain as well as carbonyl groups or
other conventional substituents. Where the term "moiety" is used to
describe a chemical compound or substituent, only an unsubstituted
chemical material is intended to be included. For example, the
phrase "alkyl group" is intended to include not only pure open
chain saturated hydrocarbon alkyl substituents, such as methyl,
ethyl, propyl, t-butyl, and the like, but also alkyl substituents
bearing further substituents known in the art, such as hydroxy,
alkoxy, alkylsulfonyl, halogen atoms, cyano, nitro, amino,
carboxyl, etc. Thus, "alkyl group" includes ether groups,
haloalkyls, nitroalkyls, carboxyalkyls, hydroxyalkyls, sulfoalkyls,
etc. On the other hand, the phrase "alkyl moiety" is limited to the
inclusion of only pure open chain saturated hydrocarbon alkyl
substituents, such as methyl, ethyl, propyl, t-butyl, and the
like.
[0036] Various precursor compounds can be used in various
combinations, optionally with one or more organic solvents
(particularly for CVD processes), to form a precursor composition.
The precursor compounds may be liquids or solids at room
temperature (preferably, they are liquids at the vaporization
temperature). Typically, they are liquids sufficiently volatile to
be employed using known vapor deposition techniques. However, as
solids they may also be sufficiently volatile that they can be
vaporized or sublimed from the solid state using known vapor
deposition techniques. If they are less volatile solids, they are
preferably sufficiently soluble in an organic solvent or have
melting points below their decomposition temperatures such that
they can be used in flash vaporization, bubbling, microdroplet
formation techniques, etc. Herein, vaporized precursor compounds
may be used either alone or optionally with vaporized molecules of
other precursor compounds or optionally with vaporized solvent
molecules, if used. As used herein, "liquid" refers to a solution
or a neat liquid (a liquid at room temperature or a solid at room
temperature that melts at an elevated temperature). As used herein,
"solution" does not require complete solubility of the solid but
may allow for some undissolved solid, as long as there is a
sufficient amount of the solid delivered by the organic solvent
into the vapor phase for chemical vapor deposition processing. If
solvent dilution is used in deposition, the total molar
concentration of solvent vapor generated may also be considered as
a inert carrier gas.
[0037] The solvents that are suitable for this application
(particularly for a CVD process) can be one or more of the
following: aliphatic hydrocarbons or unsaturated hydrocarbons
(C3-C20, and preferably C5-C10, cyclic, branched, or linear),
aromatic hydrocarbons (C5-C20, and preferably C5-C10), halogenated
hydrocarbons, silylated hydrocarbons such as alkylsilanes,
alkylsilicates, ethers, polyethers, thioethers, esters, lactones,
ammonia, amides, amines (aliphatic or aromatic, primary, secondary,
or tertiary), polyamines, nitrites, cyanates, isocyanates,
thiocyanates, silicone oils, alcohols, or compounds containing
combinations of any of the above or mixtures of one or more of the
above. The compounds are also generally compatible with each other,
so that mixtures of variable quantities of the precursor compounds
will not interact to significantly change their physical
properties.
[0038] The precursor compounds can be vaporized in the presence of
an inert carrier gas if desired. Additionally, an inert carrier gas
can be used in purging steps in an ALD process. The inert carrier
gas is typically selected from the group consisting of nitrogen,
helium, argon, and mixtures thereof. In the context of the present
invention, an inert carrier gas is one that is generally unreactive
with the complexes described herein and does not interfere with the
formation of the desired metal-containing film (i.e., layer).
[0039] The deposition process for this invention is a vapor
deposition process. Vapor deposition processes are generally
favored in the semiconductor industry due to the process capability
to quickly provide highly conformal layers even within deep
contacts and other openings. Chemical vapor deposition (CVD) and
atomic layer deposition (ALD) are two vapor deposition processes
often employed to form thin, continuous, uniform, metal-containing
(preferably, barrier) layers onto semiconductor substrates. Using
either vapor deposition process, typically one or more precursor
compounds are vaporized in a deposition chamber to form a
metal-containing layer on a substrate. It will be readily apparent
to one skilled in the art that the vapor deposition process may be
enhanced by employing various related techniques such as plasma
assistance, photo assistance, laser assistance, as well as other
techniques.
[0040] The final layer (preferably, a dielectric layer) formed
preferably has a thickness in the range of about 10 .ANG. to about
500 .ANG.. More preferably, the thickness of the metal-containing
layer is in the range of about 30 .ANG. to about 80 .ANG..
[0041] Chemical vapor deposition (CVD) has been extensively used
for the preparation of metal-containing layers, such as dielectric
layers, in semiconductor processing because of its ability to
provide highly conformal and high quality dielectric layers at
relatively fast processing times. The desired precursor compounds
are vaporized and then introduced into a deposition chamber
containing a heated substrate with optional inert carrier gases. In
a typical CVD process, vaporized precursors are contacted at the
substrate surface to form a layer (e.g., barrier layer). The single
deposition cycle is allowed to continue until the desired thickness
of the layer is achieved.
[0042] Typical CVD processes generally employ precursor compounds
in vaporization chambers that are separated from the process
chamber wherein the deposition surface or wafer is located. For
example, liquid precursor compounds are typically placed in
bubblers and heated to a temperature at which they vaporize, and
the vaporized liquid precursor compound is then transported by an
inert carrier gas passing over the bubbler or through the liquid
precursor compound. The vapors are then swept through a gas line to
the deposition chamber for depositing a layer on substrate
surface(s) therein. Many techniques have been developed to
precisely control this process. For example, the amount of
precursor material transported to the deposition chamber can be
precisely controlled by the temperature of the reservoir containing
the precursor compounds and by the flow of an inert carrier gas
bubbled through or passed over the reservoir.
[0043] Preferred embodiments of the precursor compounds described
herein are particularly suitable for chemical vapor deposition
(CVD). The deposition temperature at the substrate surface is
preferably held at a temperature in a range of about 100.degree. C.
to about 600.degree. C., more preferably in the range of about
200.degree. C. to about 500.degree. C. The deposition chamber
pressure is preferably maintained at a deposition pressure of about
0.1 torr to about 10 torr. The partial pressure of precursor
compounds in the inert carrier gas is preferably about 0.001 torr
to about 10 torr.
[0044] Several modifications of the CVD process and chambers are
possible, for example, using atmospheric pressure chemical vapor
deposition, low pressure chemical vapor deposition (LPCVD), plasma
enhanced chemical vapor deposition (PECVD), hot wall or cold wall
reactors or any other chemical vapor deposition technique.
Furthermore, pulsed CVD can be used, which is similar to ALD
(discussed in greater detail below) but does not rigorously avoid
intermixing of percursor streams. Also, for pulsed CVD, the
deposition thickness is dependent on the exposure time, as opposed
to ALD, which is self-limiting (discussed in greater detail
below).
[0045] A typical CVD process may be carried out in a chemical vapor
deposition reactor, such as a deposition chamber available under
the trade designation of 7000 from Genus, Inc. (Sunnyvale, Calif.),
a deposition chamber available under the trade designation of 5000
from Applied Materials, Inc. (Santa Clara, Calif.), or a deposition
chamber available under the trade designation of Prism from
Novelus, Inc. (San Jose, Calif.). However, any deposition chamber
suitable for performing CVD may be used.
[0046] Alternatively, and preferably, the vapor deposition process
employed is a multi-cycle ALD process. Typically, this process
provides for optimum control of atomic-level thickness and
uniformity to the deposited layer (e.g., barrier layer) and to
expose the metal precursor compounds to lower volatilization and
reaction temperatures to minimize degradation. Typically, in an ALD
process, each reactant is pulsed sequentially onto a suitable
substrate, typically at deposition temperatures of about 25.degree.
C. to about 400.degree. C. (preferably about 150.degree. C. to
about 300.degree. C.), which is generally lower than presently used
in CVD processes. Under such conditions the film growth is
typically self-limiting (i.e., when the reactive sites on a surface
are used up in an ALD process, the deposition generally stops),
insuring not only excellent conformality but also good large area
uniformity plus simple and accurate thickness control. Due to
alternate dosing of the precursor compounds, detrimental
vapor-phase reactions are inherently eliminated, in contrast to the
CVD process that is carried out by continuous coreaction of the
precursors. (See Vehkamaki et al, "Growth of SrTiO.sub.3 and
BaTiO.sub.3 Thin Films by Atomic Layer Deposition," Electrochemical
and Solid-State Letters, 2(10):504-506 (1999)).
[0047] A typical ALD process includes exposing an initial substrate
to a first chemical species (e.g., refractory metal precursor
compound of the formula MY.sub.n) to accomplish chemisorption of
the species onto the substrate. Theoretically, the chemisorption
forms a monolayer that is uniformly one atom or molecule thick on
the entire exposed initial substrate. In other words, a saturated
monolayer. Practically, chemisorption might not occur on all
portions of the substrate. Nevertheless, such an imperfect
monolayer is still a monolayer in the context of the present
invention. In many applications, merely a substantially saturated
monolayer may be suitable. A substantially saturated monolayer is
one that will still yield a deposited layer exhibiting the quality
and/or properties desired for such layer.
[0048] The first species is purged from over the substrate and a
second chemical species (e.g., a different compound of the formula
TaY.sub.5, a metal-containing precursor compound of a formula
different than TaY.sub.5, or a silicon precursor compound) is
provided to react with the first monolayer of the first species.
The second species is then purged and the steps are repeated with
exposure of the second species monolayer to the first species. In
some cases, the two monolayers may be of the same species. As an
option, the second species can react with the first species, but
not chemisorb additional material thereto. That is, the second
species can cleave some portion of the chemisorbed first species,
altering such monolayer without forming another monolayer thereon.
Also, a third species or more may be successively chemisorbed (or
reacted) and purged just as described for the first and second
species.
[0049] Purging may involve a variety of techniques including, but
not limited to, contacting the substrate and/or monolayer with a
carrier gas and/or lowering pressure to below the deposition
pressure to reduce the concentration of a species contacting the
substrate and/or chemisorbed species. Examples of carrier gases
include N.sub.2, Ar, He, etc. Purging may instead include
contacting the substrate and/or monolayer with any substance that
allows chemisorption by-products to desorb and reduces the
concentration of a contacting species preparatory to introducing
another species. The contacting species may be reduced to some
suitable concentration or partial pressure known to those skilled
in the art based on the specifications for the product of a
particular deposition process.
[0050] ALD is often described as a self-limiting process, in that a
finite number of sites exist on a substrate to which the first
species may form chemical bonds. The second species might only bond
to the first species and thus may also be self-limiting. Once all
of the finite number of sites on a substrate are bonded with a
first species, the first species will often not bond to other of
the first species already bonded with the substrate. However,
process conditions can be varied in ALD to promote such bonding and
render ALD not self-limiting. Accordingly, ALD may also encompass a
species forming other than one monolayer at a time by stacking of a
species, forming a layer more than one atom or molecule thick.
[0051] The described method indicates the "substantial absence" of
the second precursor (i.e., second species) during chemisorption of
the first precursor since insignificant amounts of the second
precursor might be present. According to the knowledge and the
preferences of those with ordinary skill in the art, a
determination can be made as to the tolerable amount of second
precursor and process conditions selected to achieve the
substantial absence of the second precursor.
[0052] Thus, during the ALD process, numerous consecutive
deposition cycles are conducted in the deposition chamber, each
cycle depositing a very thin metal-containing layer (usually less
than one monolayer such that the growth rate on average is from
about 0.2 to about 3.0 Angstroms per cycle), until a layer of the
desired thickness is built up on the substrate of interest. The
layer deposition is accomplished by alternately introducing (i.e.,
by pulsing) refractory metal precursor compound(s) and silicon
precursor compound(s) into the deposition chamber containing a
semiconductor substrate, chemisorbing the precursor compound(s) as
a monolayer onto the substrate surfaces, and then reacting the
chemisorbed precursor compound(s) with the other co-reactive
precursor compound(s). The pulse duration of precursor compound(s)
and inert carrier gas(es) is sufficient to saturate the substrate
surface. Typically, the pulse duration is from about 0.1 to about 5
seconds, preferably from about 0.2 to about 1 second.
[0053] In comparison to the predominantly thermally driven CVD, ALD
is predominantly chemically driven. Accordingly, ALD is often
conducted at much lower temperatures than CVD. During the ALD
process, the substrate temperature is maintained at a temperature
sufficiently low to maintain intact bonds between the chemisorbed
precursor compound(s) and the underlying substrate surface and to
prevent decomposition of the precursor compound(s). The temperature
is also sufficiently high to avoid condensation of the precursor
compounds(s). Typically the substrate temperature is kept within
the range of about 25.degree. C. to about 400.degree. C.
(preferably about 150.degree. C. to about 300.degree. C.), which is
generally lower than presently used in CVD processes. Thus, the
first species or precursor compound is chemisorbed at this
temperature. Surface reaction of the second species or precursor
compound can occur at substantially the same temperature as
chemisorption of the first precursor or, less preferably, at a
substantially different temperature. Clearly, some small variation
in temperature, as judged by those of ordinary skill, can occur but
still be a substantially same temperature by providing a reaction
rate statistically the same as would occur at the temperature of
the first precursor chemisorption. Chemisorption and subsequent
reactions could instead occur at exactly the same temperature.
[0054] For a typical ALD process, the pressure inside the
deposition chamber is kept at about 10.sup.-4 torr to about 1 torr,
preferably about 10.sup.-4 torr to about 0.1 torr. Typically, the
deposition chamber is purged with an inert carrier gas after the
vaporized precursor compound(s) have been introduced into the
chamber and/or reacted for each cycle. The inert carrier gas(es)
can also be introduced with the vaporized precursor compound(s)
during each cycle.
[0055] The reactivity of a precursor compound can significantly
influence the process parameters in ALD. Under typical CVD process
conditions, a highly reactive compound may react in the gas phase
generating particulates, depositing prematurely on undesired
surfaces, producing poor films, and/or yielding poor step coverage
or otherwise yielding non-uniform deposition. For at least such
reason, a highly reactive compound might be considered not suitable
for CVD. However, some compounds not suitable for CVD are superior
ALD precursors. For example, if the first precursor is gas phase
reactive with the second precursor, such a combination of compounds
might not be suitable for CVD, although they could be used in ALD.
In the CVD context, concern might also exist regarding sticking
coefficients and surface mobility, as known to those skilled in the
art, when using highly gas-phase reactive precursors, however,
little or no such concern would exist in the ALD context.
[0056] As stated above, the use of the complexes and methods of
forming films of the present invention are beneficial for a wide
variety of thin film applications in semiconductor structures. For
example, such applications include capacitors such as planar cells,
trench cells (e.g., double sidewall trench capacitors), stacked
cells (e.g., crown, V-cell, delta cell, multi-fingered, or
cylindrical container stacked capacitors), as well as field effect
transistor devices.
[0057] Use of the barrier layers of the present invention in
semiconductor constructions shall be described generally with
reference to FIGS. 1 and 2.
[0058] FIG. 1 illustrates a structure 10 including a substrate
assembly 11 and a tantalum silicide (preferably, a tantalum silicon
nitride) diffusion barrier layer 13 according to the present
invention formed on a surface 12 of the substrate assembly 11,
e.g., a silicon containing surface. The structure 10 further
includes a conductive layer 14 (e.g., a copper layer). The
structure 10 is illustrative of the use of a tantalum silicide
diffusion barrier layer for any application requiring an effective
barrier layer, for example, to prevent diffusion from a silicon
containing surface. In other words, the tantalum silicide
(preferably, a tantalum silicon nitride) diffusion barrier layer 13
may be used in the fabrication of semiconductor devices wherever it
is necessary to prevent the diffusion of one material to an
adjacent material. For example, the substrate assembly 11 may be
representative of a contact structure having an opening extending
to a silicon containing surface. In such a structure, diffusion
barriers are commonly used in such openings to prevent undesirable
reactions, such as the reaction of a conductive contact material,
e.g, copper or aluminum, with the silicon containing surface.
[0059] Further, for example, the tantalum silicide diffusion
barrier layer 13 may be used in the formation of storage cell
capacitors for use in semiconductor devices, e.g., memory devices.
As further described herein, the tantalum silicide diffusion
barrier layer is used within a stack of layers forming an electrode
of a capacitor, e.g., the other layers including layers formed of
materials such as platinum, ruthenium oxide, etc. One skilled in
the art will recognize that various semiconductor processes and
structures for various devices, e.g., CMOS devices, memory devices,
etc., would benefit from the barrier characteristics of the barrier
layers of the present invention and in no manner is the present
invention limited to the illustrative embodiments described
herein.
[0060] FIG. 2 shows a structure 50 including substrate assembly 52
(e.g., a silicon substrate) and capacitor structure 54 formed
relative thereto. Capacitor structure 54 includes a first electrode
56, a second electrode 60, and a high dielectric constant layer 58
interposed therebetween. For example, the dielectric layer may be
any suitable material having a desirable dielectric constant, such
as TiO.sub.2, ZrO.sub.2, HfO.sub.2, Ta.sub.2O.sub.5,
(Ba,Sr)TiO.sub.3, Pb(Zr,Ti)O.sub.3, or SrBi.sub.2Ti.sub.2O.sub.9.
With use of the high dielectric constant layer 58, diffusion
barrier properties of the electrodes is particularly important. For
example, to function well in a bottom electrode of a capacitor
structure, the electrode layer or electrode stack must act as an
effective barrier to the diffusion of silicon, particularly due to
the processes used to form the high dielectric constant materials.
Such diffusion barrier properties are required when the substrate
assembly 52 includes a silicon-containing surface 53 upon which the
capacitor is formed, e.g., polysilicon, silicon substrate material,
N-doped silicon, P-doped silicon, etc., since oxidation of the
diffused silicon to form silicon dioxide may result in degraded
capacitance, e.g., capacitance for a memory device. In addition,
the electrode stack must act as an oxygen barrier (e.g., diffusion
barrier layer 62) to protect the silicon-containing surface under
the stack from oxidizing. The formation of the tantalum silicide
(preferably, tantalum silicon nitride) diffusion barrier layer
enhances the barrier properties of the stack.
[0061] A system that can be used to perform vapor deposition
processes (chemical vapor deposition or atomic layer deposition) of
the present invention is shown in FIG. 3. The system includes an
enclosed vapor deposition chamber 110, in which a vacuum may be
created using turbo pump 112 and backing pump 114. One or more
substrates 116 (e.g., semiconductor substrates or substrate
assemblies) are positioned in chamber 110. A constant nominal
temperature is established for substrate 116, which can vary
depending on the process used. Substrate 116 may be heated, for
example, by an electrical resistance heater 118 on which substrate
116 is mounted. Other known methods of heating the substrate may
also be utilized.
[0062] In this process, precursor compounds 160 (e.g., a tantalum
precursor compound and a silicon precursor compound) are stored in
vessels 162. The precursor compounds are vaporized and separately
fed along lines 164 and 166 to the deposition chamber 110 using,
for example, an inert carrier gas 168. A reaction gas 170 (although
for the present invention, reaction gases are not necessary or
desirable) may be supplied along line 172 as needed. Also, a purge
gas 174, which is often the same as the inert carrier gas 168, may
be supplied along line 176 as needed. As shown, a series of valves
180-185 are opened and closed as required.
[0063] The following examples are offered to further illustrate the
various specific and preferred embodiments and techniques. It
should be understood, however, that many variations and
modifications may be made while remaining within the scope of the
present invention, so the scope of the invention is not intended to
be limited by the examples.
EXAMPLE
Example 1
Pulsed Chemical Vapor Deposition of Tantalum Silicide
[0064] Using a pulsed CVD method, the following precursor compounds
were pulsed for 200 cycles in a deposition chamber as described in
FIG. 3 containing a borophosphosilicate glass (BPSG) substrate,
each cycle consisting of pulses in the following order: (1)
tantalum pentafluoride (Alfa Aesar, Ward Hill, Mass.; and (2)
disilane (VOC Gases). During each cycle, excess amounts of each
precursor compound not chemisorbed were purged from the chamber
after chemisorption and prior to the introduction of the next
precursor compound using an argon sweep at 30 mL/min and a vacuum
pump. The substrate temperature was kept at approximately
275.degree. C. throughout the entire deposition process.
[0065] At the end of the process, a 1700 .ANG. thick miffor-like
layer of tantalum silicide was formed having a resistivity of 255
.mu..OMEGA.-cm. The layer contained tantalum, silicon, and a trace
of oxygen as determined by x-ray photoelectron spectroscopy (XPS)
analysis. X-ray diffraction analysis (XRD) showed the layer to be
crystalline TaSi.sub.2, as measured immediately after the process
was completed.
[0066] The complete disclosures of the patents, patent documents,
and publications cited herein are incorporated by reference in
their entirety as if each were individually incorporated. Various
modifications and alterations to this invention will become
apparent to those skilled in the art without departing from the
scope and spirit of this invention. It should be understood that
this invention is not intended to be unduly limited by the
illustrative embodiments and examples set forth herein and that
such examples and embodiments are presented by way of example only
with the scope of the invention intended to be limited only by the
claims set forth herein as follows.
* * * * *