U.S. patent application number 11/301043 was filed with the patent office on 2006-05-11 for silicon source reagent compositions, and method of making and using same for microelectronic device structure.
Invention is credited to Thomas H. Baum, Brian L. Benac, Alexander S. Borovik, Ziyun Wang, Chongying Xu.
Application Number | 20060099831 11/301043 |
Document ID | / |
Family ID | 28789776 |
Filed Date | 2006-05-11 |
United States Patent
Application |
20060099831 |
Kind Code |
A1 |
Borovik; Alexander S. ; et
al. |
May 11, 2006 |
Silicon source reagent compositions, and method of making and using
same for microelectronic device structure
Abstract
A method of synthesizing an aminosilane source reagent
composition, by reacting an aminosilane precursor compound with an
amine source reagent compound in a solvent medium comprising at
least one activating solvent component, to yield an aminosilane
source reagent composition having less than 1000 ppm halogen.
Inventors: |
Borovik; Alexander S.;
(Hartford, CT) ; Wang; Ziyun; (New Milford,
CT) ; Xu; Chongying; (New Milford, CT) ; Baum;
Thomas H.; (New Fairfield, CT) ; Benac; Brian L.;
(Austin, TX) |
Correspondence
Address: |
INTELLECTUAL PROPERTY / TECHNOLOGY LAW
PO BOX 14329
RESEARCH TRIANGLE PARK
NC
27709
US
|
Family ID: |
28789776 |
Appl. No.: |
11/301043 |
Filed: |
December 12, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10112517 |
Mar 29, 2002 |
|
|
|
11301043 |
Dec 12, 2005 |
|
|
|
09954831 |
Sep 18, 2001 |
6869638 |
|
|
10112517 |
Mar 29, 2002 |
|
|
|
09823196 |
Mar 30, 2001 |
7005392 |
|
|
09954831 |
Sep 18, 2001 |
|
|
|
Current U.S.
Class: |
438/791 ;
257/E21.263; 257/E21.293; 427/585; 438/794; 548/110 |
Current CPC
Class: |
H01L 21/02219 20130101;
H01L 21/02271 20130101; H01L 21/02222 20130101; C07F 7/025
20130101; H01L 21/28167 20130101; H01L 29/518 20130101; C07F 7/10
20130101; H01L 21/02164 20130101; H01L 21/02148 20130101; C07F
7/003 20130101; H01L 21/28194 20130101; H01L 29/517 20130101; C23C
16/405 20130101; C23C 16/401 20130101 |
Class at
Publication: |
438/791 ;
438/794; 427/585; 548/110 |
International
Class: |
H01L 21/469 20060101
H01L021/469 |
Claims
1. A CVD precursor composition for forming a silicon-containing
thin film on a substrate, said precursor composition including at
least one aminosilane source reagent composition selected from the
group consisting of: ##STR10## wherein R.sup.3 is selected from the
group consisting of hydrogen, C.sub.1-C.sub.4 alkyl, and
C.sub.1-C.sub.4 alkoxy; x is from 0 to 3; Si is silicon; A is
halogen; y is from 0 to 3; N is nitrogen; each of R.sup.1 and
R.sup.2 is same or different and is independently selected from the
group consisting of H, aryl, perfluoroaryl, C.sub.1-C.sub.8 alkyl,
and C.sub.1-C.sub.8 perfluoroalkyl; and n is from 1-6.
2. The composition of claim 1, wherein said aminosilane source
reagent composition is made by: (a) reacting an aminosilane
precursor compound with an amine source reagent compound, wherein
the amine source reagent compound is selected from the group
consisting of: ##STR11## wherein B is selected from the group
consisting of H, Li, Na, K, Zn and MgBr; N is nitrogen; R.sup.1 and
R.sup.2 are same or different and each is independently selected
from the group consisting of H, aryl, perfluoroaryl,
C.sub.1-C.sub.8 alkyl, and C.sub.1-C.sub.8 perfluoroalkyl; and n is
from 1-6, in a solvent system comprising at least one non-polar
solvent, at temperature in a range from about -30.degree. C. to
about room temperature, for a period of time sufficient to produce
a reaction mixture comprising partially substituted aminosilane
components, unreacted aminosilane precursors and unreacted amine
components; (b) combining the reaction mixture with at least one
polar activating solvent component to at least partially solvate
and activate the unreacted amine components, wherein the polar
activating solvent comprises a Lewis base selected from the group
consisting of ethers and tertiary amines; and (c) continuing the
reaction of step (b) at temperature in a range from about 0.degree.
C. to about 100.degree. C. for a period of time sufficient to
produce the aminosilane source reagent composition, wherein the
aminosilane source reagent composition comprises less than 1000 ppm
halogen.
3. The CVD precursor composition according to claim 2, wherein the
polar activating solvent is selected from the group consisting of:
diethyl ether, tetrahydrofuran (THF), ethylene glycol dimethyl
ether (glyme), diethylene glycol dimethyl ether (diglyme),
1,4-dioxane, tetraethylene glycol dimethyl ether (tetraglyme),
1,4,7,10-tetraoxacyclododecane (12-Crown-4),
1,4,7,10,13-pentaoxacyclopentadecane (15-Crown-5), and
1,4,7,10,13,16-hexaoxacyclooctadecane (18-Crown-6),
pentamethyldiethylenetriamine (PMDETA), tetramethylethylene-diamine
(TMEDA), Triethylamine; (TEA) Diazabicycloun-decene (DBU),
Tri-n-butylamine (TNBA), and tetraethylethylenediamine (TEDA).
4. The composition of claim 1, wherein said aminosilane source
reagent composition is made by: (1) combining an aminosilane
precursor compound comprising at least one halogen leaving group,
with an amine source reagent compound, in a solvent system
comprising at least one non-polar solvent, for a period of time
sufficient to produce a reaction mixture consisting essentially of
partially substituted aminosilane components, unreacted aminosilane
precursors and unreacted amine components; (2) removing the
non-polar solvent from the reaction mixture; (3) combining with the
reaction mixture of step (2) a polar activating solvent to at least
partially solvate and activate the unreacted amine components; (4)
continuing the reaction of step (3) for a period of time sufficient
to provide for essentially stoichiometric substitution of at least
one halide on the aminosilane precursor compound by an amine
component to produce the aminosilane source reagent
composition.
5. The method according to claim 4, wherein the non-polar solvent
is removed by vacuum evaporation.
6. The method according to claim 4, wherein the reaction of steps
(2) and (3) is carried out at a temperature that is in the range of
from about -30.degree. C. to room temperature.
7. The CVD precursor composition according to claim 1, further
comprising at least one metalloamide source reagent composition
selected from the group consisting of: ##STR12## wherein M is
selected from the group consisting of: Zr, Hf, Y, La, Lanthanide
series elements, Ta, Ti, Al; N is nitrogen; each of R.sup.1 and
R.sup.2 is same or different and is independently selected from the
group consisting of H, aryl, perfluoroaryl, C.sub.1-C.sub.8 alkyl,
C.sub.1-C.sub.8 perfluoroalkyl, alkylsilyl; x is the oxidation
state on metal M; and n is from 1-6.
8. The CVD precursor composition according to claim 1, further
comprising at least one metalloamide source reagent composition
having a formula: M(NR.sub.2).sub.x(NR'.sub.2).sub.y wherein M is
selected from the group consisting of: Y, Hf, La, and Ta; N is
nitrogen, each of R and R' is independently selected from the group
consisting of H, aryl, perfluoroaryl, C.sub.1-C.sub.8 alkyl,
C.sub.1-C.sub.8 perfluoroalkyl, and alkylsilyl; (NR.sub.2).sub.x
and (NR'.sub.2).sub.y are different amino ligands and R' is
different from R; x is from 1 to 5; y is from 1 to 5; and x+y is
equal to the oxidation state of metal M, and a solvent medium,
wherein the metalloamide source reagent compound is soluble or
suspendable therein.
9. The CVD precursor composition according to claim 8, wherein the
solvent medium is selected from the group consisting of: ethers,
glymes, tetraglymes, amines, polyamines, alcohols, glycols,
aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents,
cyclic ethers and combinations of two or more of the foregoing.
10. A CVD method of forming a silicon-containing thin film on a
substrate, comprising: vaporizing the CVD precursor composition of
claim 1 to form a source reagent precursor vapor; transporting the
source reagent precursor vapor into a chemical vapor deposition
zone, optionally using a carrier gas; and contacting the source
reagent precursor vapor with a substrate in said chemical vapor
deposition zone at elevated temperature to deposit the silicon
containing thin film on the substrate.
11. A CVD method of forming a silicon-containing thin film on a
substrate, comprising: vaporizing the CVD precursor composition of
claim 8 to form a source reagent precursor vapor; transporting the
source reagent precursor vapor into a chemical vapor deposition
zone, optionally using a carrier gas; and contacting the source
reagent precursor vapor with a substrate in said chemical vapor
deposition zone at elevated temperature to deposit the silicon
containing thin film on the substrate.
12. A liquid CVD precursor composition for forming a
silicon-containing thin film on a substrate, said precursor
composition including (a) at least one aminosilane source reagent
composition selected from the group consisting of: ##STR13##
wherein R.sup.3 is selected from the group consisting of hydrogen,
C.sub.1-C.sub.4 alkyl, and C.sub.1-C.sub.4 alkoxy; x is from 0 to
3; Si is silicon; A is halogen; y is from 0 to 3; N is nitrogen;
each of R.sup.1 and R.sup.2 is same or different and is
independently selected from the group consisting of H, aryl,
perfluoroaryl, C.sub.1-C.sub.8 alkyl, and C.sub.1-C.sub.8
perfluoroalkyl; and n is from 1-6; and (b) at least one
metalloamide source reagent composition having a formula:
M(NR.sub.2).sub.x(NR'.sub.2).sub.y wherein M is selected from the
group consisting of: Y, Hf, La, and Ta; N is nitrogen, each of R
and R is independently selected from the group consisting of H,
aryl, perfluoroaryl, C.sub.1-C.sub.8 alkyl, C.sub.1-C.sub.8
perfluoroalkyl, and alkylsilyl; (NR.sub.2).sub.x and
(NR'.sub.2).sub.y are different amino ligands and R' is different
from R; x is from 1 to 5; y is from 1 to 5; and x+y is equal to the
oxidation state of metal M, and a solvent medium, wherein the
metalloamide source reagent compound is soluble or suspendable
therein.
13. The CVD precursor composition according to claim 9, wherein the
solvent medium is selected from the group consisting of: ethers,
glymes, tetraglymes, amines, polyamines, alcohols, glycols,
aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents,
cyclic ethers and combinations of two or more of the foregoing.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of U.S. patent application Ser. No.
10/112,517 filed on Mar. 29, 2002 in the name of Alexander S.
Borovik et al., which is a continuation-in-part of U.S. patent
application Ser. No. 09/954,831 filed on Sep. 18, 2001 in the name
of Thomas H. Baum et al., which is a continuation-in-part of U.S.
patent application Ser. No. 09/823,196 filed on Mar. 30, 2001 in
the name of Thomas H. Baum et al. The disclosures of all of the
foregoing applications are hereby incorporated herein in their
respective entireties, for all purposes, and the priority of all
such applications is hereby claimed under the provisions of 35 USC
120.
FIELD OF THE INVENTION
[0002] The present invention relates to silicon precursor
compositions and their synthesis, and to the use of such silicon
precursor compositions for the fabrication of microelectronic
device structures, e.g., in the formation of gate dielectrics and
silicon nitride barrier layers, in the manufacture of semiconductor
integrated circuits, or in otherwise forming silicon-containing
films on a substrate by chemical vapor deposition (CVD) utilizing
such precursor compositions.
BACKGROUND OF THE INVENTION
[0003] The process of fabricating semiconductor integrated circuits
generally includes the formation of such components as, gate
oxides, high k dielectrics, low k dielectrics, barrier layers, etch
stop layers and gate spacers. Such components often include silicon
or silicon oxide in their compositions. For example, conventional
gate dielectric materials may be formed from silicon dioxide,
silicon oxy-nitride, silicon nitride or metal silicates.
[0004] Semiconductor devices such as field effect transistors (FET)
and metal oxide semiconductor capacitors (MOS-caps), which are
common in the electronics industry, include many of the components
identified above. Such devices may be formed with dimensions that
enable thousands or even millions of devices to be formed on a
single-crystal substrate and interconnected to perform useful
functions in an integrated circuit such as a microprocessor.
[0005] The general structure and operation of a field effect
transistor is as follows. With reference to FIG. 1, a simplified
field effect transistor is shown in cross-section. In a field
effect transistor a portion of the substrate (or epi-layer) 100
near the surface is designated as the channel 120 during
processing. Channel 120 is electrically connected to source 140 and
drain 160, such that when a voltage difference exists between
source 140 and drain 160, current will tend to flow through channel
120. The semiconducting characteristics of channel 120 are altered
such that its resistivity may be controlled by the voltage applied
to gate 200, a conductive layer overlying channel 120. Thus by
changing the voltage on gate 200, more or less current can be made
to flow through channel 120. Gate 200 and channel 120 are separated
by gate dielectric 180; the gate dielectric is insulating, such
that between gate 200 and channel 120 the current flow during
operation is small compared to the source to drain current
(although "tunneling" current is observed with thin dielectrics.)
However, the gate dielectric allows the gate voltage to induce an
electric field in channel 120, giving rise to the name "field
effect transistor." The general structure of a MOS-cap can be
visualized as layers 200, 180 and 120 of FIG. 1 without the source
and drain. The MOS-cap functions as a capacitor.
[0006] SiO.sub.2 represents the highest quality gate dielectric
material 180 so far developed in silicon technology with low
defects and low surface state density. One important advantage of
SiO.sub.2 is that it may be grown from the silicon substrate at
elevated temperatures in an oxidizing environment. It is well known
in the art, that thermally grown oxides tend to have fewer defects,
(i.e. pinholes), than deposited materials. Thus, SiO.sub.2 has
persisted as the dielectric material in most silicon device
structures.
[0007] Generally, integrated circuit performance and density may be
enhanced by decreasing the size of the individual semiconductor
devices on a chip. Unfortunately, field effect semiconductor
devices produce an output signal that is proportional to the length
of the channel, such that scaling reduces their output. This effect
has generally been compensated for by decreasing the thickness of
gate dielectric 180, thus bringing the gate in closer proximity to
the channel and enhancing the field effect.
[0008] As devices have scaled to smaller and smaller dimensions,
the gate dielectric thickness has continued to shrink. Although
further scaling of devices is still possible, scaling of the gate
dielectric thickness has almost reached its practical limit with
the conventional gate dielectric materials: silicon dioxide,
silicon oxy-nitride and silicon nitride. Further scaling of silicon
dioxide gate dielectric thickness will involve problems such as:
extremely thin layers allowing for large leakage currents due to
direct tunneling through the oxide. Because such layers are formed
literally from a few atomic layers, exact process control is
required to repeatably produce such layers. Uniformity of coverage
is also critical because device parameters may change dramatically
based on the presence or absence of even a single monolayer of
dielectric material. Finally, such thin layers form poor diffusion
barriers to impurities and dopants.
[0009] Consequently, there is a need in the art for alternative
dielectric materials, which can be formed in a thicker layer than
silicon dioxide and yet still produce the same field effect
performance. This performance is often expressed as "equivalent
oxide thickness" (EOT). Although the alternative material layer may
be thick, it has the equivalent effect of a much thinner layer of
silicon dioxide (commonly called simply "oxide"). In order to have
a physically thick layer with a low EOT, the dielectric constant of
the insulating material must be increased. Many, if not most, of
the attractive alternatives for achieving low equivalent oxide
thicknesses are metal oxides, such as tantalum pentoxide, titanium
dioxide, barium strontium titanate and other suitable thin
films.
[0010] However, the formation of such metal oxides as gate
dielectrics has been found to be problematic. At typical metal
oxide deposition temperatures, the oxygen co-reactant or
oxygen-containing precursor tends to oxidize the silicon substrate,
producing a lower dielectric constant oxide layer at the interface
between the substrate and the higher dielectric constant, gate
dielectric material. It could be that the transition metal oxide
acts as a catalytic source of activated oxygen, that the precursor
molecules increase the oxygen activity or that oxygen from the
precursor is incorporated in the growing oxide film. Whatever the
cause, the presence of this interfacial oxide layer increases the
effective oxide thickness, reducing the effectiveness of the
alternative gate dielectric material. The existence of the
interfacial oxide layer places a severe constraint on the
performance of an alternative dielectric field effect device and
therefore, is unacceptable.
[0011] The use of metal oxide and metal oxy-nitride thin films
comprising Zr, Hf, Y, La, Lanthanide series elements, Ta, Ti and/or
Al and silicates of these metal oxides and metal oxy-nitrides are
regarded as potential material replacements of the SiO.sub.2 gate
oxides, (i.e., U.S. Pat. Nos. 6,159,855 and 6,013,553). However, to
ensure a high integrity interface between the silicon and the gate
dielectric film these films must be deposited at relatively low
temperatures.
[0012] The source reagents and methodology employed to form such
gate dielectric thin films are extremely critical for the provision
of a gate structure having satisfactory electrical performance
characteristics in the product device. Specifically, the source
reagents and methodology must permit the gate dielectric thin film
to form on a clean silicon surface, without the occurrence of side
reactions producing predominantly silicon dioxide (SiO.sub.2),
locally doped SiO.sub.2 and/or other impurities, that lower the
dielectric constant and compromise the performance of the product
microelectronic device. Accordingly, the absence of impurities is
highly desirable.
[0013] Chemical vapor deposition (CVD) is the thin film deposition
method of choice for high-density, large-scale fabrication of
microelectronic device structures, and the semiconductor
manufacturing industry has extensive expertise in its use.
Metalorganic CVD (MOCVD) and more particularly atomic layer CVD
(ALCVD) are particularly advantageous processes because they allow
for lower deposition temperatures and stricter control of the
stoichiometry and thickness of the formed layer.
[0014] In the formation of gate dielectrics and other semiconductor
manufacturing applications it is essential to control the
composition of the deposited thin film. The molar ratio(s) of the
different elements in the thin film typically corresponds very
closely to a predetermined value. Therefore, it is very important
to select a precursor delivery system that allows for strict
control of the precursors delivered into the CVD chamber. Precursor
delivery systems are well known in the art of CVD, (i.e., U.S. Pat.
No. 5,820,678, entitled "Solid Source MOCVD System" describes the
bubbler delivery approach and U.S. Pat. No. 5,204,314, entitled
"Method for Delivering an Involatile Reagent in Vapor Form to a CVD
Reactor," and U.S. Pat. No. 5,536,323, entitled "Apparatus for
Flash Vaporization Delivery of Reagents," describe the liquid
delivery, flash vaporization approach).
[0015] Chemical vapor deposition (CVD) of silicon-containing films
provides uniform coverage. Liquid CVD precursors enable direct
delivery or liquid injection of the precursors into a CVD vaporizer
unit. The accurate and precise delivery rate can be obtained
through volumetric metering to achieve reproducible CVD
metallization during VLSI device manufacturing.
[0016] Impurities that are known to lower the dielectric constant
and/or increase leakage include among others, carbon and halides.
Carbon and/or halide incorporation into the dielectric thin film
would degrade leakage, dielectric constant, and overall electrical
performance of the thin film. In contrast, nitrogen incorporation
may exhibit some beneficial properties on the dielectric thin
film.
[0017] Excess halide may adversely affect a gate dieletric thin
film in either of two ways. Halide incorporation into a gate
dielectric thin film, may directly affect the electronic nature of
the film, thereby reducing device lifetime. Secondly, halide, such
as chloride, leads to formation of hydrogen chloride during the
decomposition of the precursor, which potentially affects the CVD
chamber making the treatment of the effluent from the chamber more
challenging.
[0018] Zr, Hf, Y, La, Lanthanide series elements, Ta, Ti, Al and/or
silicon source reagents, specifically Zr and Hf-containing
silicates such as Zr.sub.xSi.sub.1-xO.sub.2, and
Hf.sub.xSi.sub.1-xO.sub.2 are of great interest for use as next
generation gate dielectrics. These materials possess dielectric
constant (k) values in the range of 10 to 20, depending on x, and
allow the use of a physical thickness to prevent leakage by
electron tunneling. Given the feature sizes of the VLSI devices,
CVD is becoming a unique technique for depositing these
materials.
[0019] In such applications, the choice of the zirconium or hafnium
CVD source reagents and a compatible silicon source reagent is of
critical importance for the successful deposition of high quality
Zr or Hf silicate gate dielectric. Low temperature CVD silicon
precursors are required to minimize the formation of interfacial
silicon dioxide. Ideally, the precursors are compatible in solution
and in vapor phase and decompose below 600.degree. C. on substrate
surfaces, forming Hf or Zr silicates in high purity and high
density with no interfacial layer.
[0020] The source reagents must be thermally stable to avoid
premature decomposition of such source reagents before they reach
the CVD reaction chamber during the CVD process. Premature
decomposition of source reagents not only results in undesirable
accumulation of side products that will clog fluid flow conduits of
the CVD apparatus, but also causes undesirable variations in
composition of the deposited gate dielectric thin film. Further,
particle formation can result in deleterious yields in device
fabrication.
[0021] Further, Zr, Hf, Y, La, Lanthanide series elements, Ta, Ti,
Al and/or silicon source reagents have to be chemically compatible
with other source reagents used in the CVD process. "Chemically
compatible" means that the source reagents will not undergo,
undesirable side reactions with other co-deposited source reagents,
and/or deleterious ligand exchange reactions that may alter the
precursor properties, such as transport behavior, incorporation
rates and film stoichiometries.
[0022] Finally, Zr, Hf, Y, La, Lanthanide series elements, Ta, Ti,
Al and/or silicon source reagents selected for MOCVD of dielectric
thin films must be able to maintain their chemical identity over
time when dissolved or suspended in organic solvents or used in
conventional bubblers. Any change in chemical identity of source
reagents in the solvent medium is deleterious since it impairs the
ability of the CVD process to achieve repeatable delivery and film
growth.
[0023] There is a continuing need in the art to provide improved
Zr, Hf, Y, La, Lanthanide series elements, Ta, Ti, Al and/or
silicon source reagents suitable for high efficiency CVD processes,
for fabricating corresponding high quality gate dielectric, thin
films.
[0024] Silicon amide source reagents are of great interest for use
as low temperature CVD precursors in many applications, e.g., CVD
of silicon nitride and early transition metal silicates. However,
many commercially available silicon amides have unacceptably high
levels of chloride.
[0025] Currently available synthetic routes result in poor yields
and/or impure material. For example, Gerard Kannengiesser and
Francois Damm, (Bull. Soc. Chim. Fr. (1967), (7), 2492-5) disclose
the method outlined by equation (1) below and report a product
yield of only about 20%.
SiCl.sub.4+4R.sub.2NMgBr.fwdarw.Si(NR.sub.2).sub.4+4MgBrCl (1)
[0026] R. Gordon, D. Hoffman and U. Riaz report (Chem. Mater. 1990,
2, 480-482) the synthesis of Si(NMe.sub.2).sub.4 using LiNMe.sub.2
and SiCl.sub.4 in toluene in 60% yield. When, the same experiment
was repeated by the inventors of the instant invention, the product
contained chlorine content too high (a few percent) for
semiconductor grade materials.
[0027] Therefore, it is one object of this invention to provide CVD
precursors and CVD processes to deposit high dielectric constant
thin films, having minimum carbon and halide incorporation and when
deposited on a silicon substrate, minimal SiO.sub.2 interlayer.
[0028] It is a further object of this invention to synthesize
aminosilane source reagents in high yield and high purity.
[0029] It is a still further object of the present invention to
provide CVD precursors and a CVD process to deposit silicon
containing thin films, having minimum carbon and halide
incorporation and when deposited on a silicon substrate, minimal
SiO.sub.2 interlayer.
[0030] It is another object of the invention to provide methods of
forming silicon-containing films in the manufacturing of integrated
circuits and other microelectronic device structures.
[0031] It is another object of the invention to provide a method of
forming silicon-containing thin films on a substrate by
metalorganic chemical vapor deposition (CVD) utilizing such novel
silicon precursors and solution compositions.
[0032] The present invention relates to novel precursor
compositions for low temperature (<600.degree. C.) chemical
vapor deposition (CVD) formation of silicon-containing films, and
to associated methods of making and using such types of
compositions.
[0033] Other objects and advantages of the present invention will
be more fully apparent from the ensuing disclosure and appended
claims.
SUMMARY OF THE INVENTION
[0034] The present invention relates to aminosilane source reagent
compositions, and to a method of making, and using the same.
[0035] In one broad aspect, the present invention relates to
silicon precursors having reduced oxygen and halogen content
(relative to various corresponding commercial silicon source
reagents) with utility for chemical vapor deposition (CVD) of
silicon containing thin films of varying types, including silicon
nitride, silicates, and doped silicate films (when a dopant
co-precursor is utilized), as well as to a method for making and
using such silicon precursors. More specifically, the silicon
precursors of the present invention comprise a composition selected
from the group consisting of: ##STR1## wherein R.sup.3 is selected
from the group consisting of hydrogen, C.sub.1-C.sub.4 alkyl, and
C.sub.1-C.sub.4 alkoxy; x is from 0 to 3; Si is silicon; A is
halogen; y is from 0 to 3; N is nitrogen; each of R.sup.1 and
R.sup.2 is same or different and is independently selected from the
group consisting of H, aryl, perfluoroaryl, C.sub.1-C.sub.8 alkyl,
and C.sub.1-C.sub.8 perfluoroalkyl; and n is from 1-6.
[0036] In a further aspect, the present invention relates to novel,
stable aminosilane source reagent compositions for chemical vapor
deposition (CVD) of silicon-containing thin films as well as to
methods of making and using same. More specifically, the present
invention relates to novel aminosilane source reagent compositions
having the formula,
R.sup.3.sub.xSiA.sub.y(NR.sup.1R.sup.2).sub.4-x-y; wherein R.sup.3
is selected from the group consisting of hydrogen, C.sub.1-C.sub.4
alkyl, and C.sub.1-C.sub.4 alkoxy; x is from 0 to 3; Si is silicon;
A is halogen; y is from 0 to 3; N is nitrogen; R.sup.1 is methyl
and R.sup.2 ethyl.
[0037] In a further aspect, the present invention relates to a
method of synthesizing an aminosilane source reagent composition,
by reacting a silicon halide source reagent compound with an amine
source reagent compound in a polar, activating solvent, to yield an
aminosilane precursor having reduced halide content as compared to
the existing commercial precursors.
[0038] In a specific aspect, the present invention provides a CVD
process that uses the aforementioned aminosilane precursors, that
may alternatively be in the form of a neat liquid, as well as
solution compositions of solid and liquid precursors of such type,
for deposition of silicon containing films (e.g., by direct liquid
injection and vaporization). Vaporization may be effected by
heating, acoustics, ultrasound or nebulization.
[0039] A still further aspect of the invention relates to a
microelectronic device structure comprising a substrate having a
chemical vapor deposited silicon-containing thin film layer on the
substrate, wherein the silicon containing layer has been formed
using a liquid-phase silicon precursor that is thermally stable at
liquid delivery temperatures (at which the precursor liquid is
vaporized to form a corresponding precursor vapor), but which is
readily decomposable at chemical vapor deposition condition
temperatures, to yield a silicon-containing film on the substrate
with which the precursor vapor is contacted
[0040] Other aspects, features, and embodiments of the invention
will be more fully apparent from the ensuing disclosure and
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] FIG. 1 is a cross-sectional view of a typical prior art
integrated circuit field effect transistor.
[0042] FIGS. 2A and 2B show a limited pressure-temperature matrix
for
Si(N(C.sub.2H.sub.5).sub.2).sub.2Cl.sub.2(bis(diethyl-amino)dichlorosilan-
e), and Si(N(CH.sub.3).sub.2).sub.3Cl
(tris(dimethyl-amino)chlorosilane in N.sub.2O.
[0043] FIG. 3 shows the growth rate of silica from
Si(N(C.sub.2H.sub.5).sub.2).sub.2Cl.sub.2
(Bis(diethyl-amino)dichlorosilane) in N.sub.2O ambient.
[0044] FIG. 4 shows the growth rate of silica from
Si(N(CH.sub.3).sub.2).sub.3Cl (Tris(dimethyl-amino)chlorosilane in
N.sub.2O ambient.
[0045] FIG. 5 shows the growth rate of SiO.sub.2 under a HfO.sub.2
film with no silicon precursor present.
[0046] FIG. 6 shows the growth rate of SiO.sub.2 from
Si(N(C.sub.2H.sub.5).sub.2).sub.2Cl.sub.2
(Bis(diethyl-amino)dichlorosilane when co-deposited with HfO.sub.2
from Hf(N(C.sub.2H.sub.5).sub.2).sub.4
(Tetrakis(diethyl-amino)hafnium in N.sub.2O ambient.
[0047] FIG. 7 shows a proton spectrum (.sup.1H NMR) of
Si(NMe.sub.2).sub.4 in (C.sub.6D.sub.6).
DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS
THEREOF
[0048] The disclosure of the following United States patents and
patent applications are hereby incorporated by reference in their
respective entireties: [0049] U.S. patent application Ser. No.
09/414,133 filed Oct. 7, 1999 in the names of Thomas H. Baum, et
al.; [0050] U.S. patent application Ser. No. 09/012,679 filed Jan.
23, 1998 in the names of Gautam Bhandari, et al., and issued Jan.
18, 2000 as U.S. Pat. No. 6,015,917; [0051] U.S. patent application
Ser. No. 08/979,465 filed Nov. 26, 1997 in the names of Frank
DiMeo, Jr., et al., and issued Oct. 26, 1999 as U.S. Pat. No.
5,972,430; [0052] U.S. patent application Ser. No. 08/835,768 filed
Apr. 8, 1997 in the names of Thomas H. Baum, et al., and issued
Jul. 6, 1999 as U.S. Pat. No. 5,919,522; [0053] U.S. patent
application Ser. No. 08/484,654 filed Jun. 7, 1995 in the names of
Robin A. Gardiner et al., and issued Aug. 29, 2000 as U.S. Pat. No.
6,110,529; [0054] U.S. patent application Ser. No. 08/414,504 filed
Mar. 31, 1995 in the names of Robin A. Gardiner et al., and issued
Oct. 13, 1998 as U.S. Pat. No. 5,820,664; [0055] U.S. patent
application Ser. No. 08/280,143 filed Jul. 25, 1994 in the names of
Peter S. Kirlin, et al., and issued July 16, 1996 as U.S. Pat. No.
5,536,323; [0056] U.S. patent application Ser. No. 07/927,134,
filed Aug. 7, 1992 in the same names; [0057] U.S. patent
application Ser. No. 07/807,807 filed Dec. 13, 1991 in the names of
Peter S. Kirlin, et al., and issued Apr. 20, 1993 as U.S. Pat. No.
5,204,314; [0058] U.S. patent application Ser. No. 08/181,800 filed
Jan. 15, 1994 in the names of Peter S. Kirlin, et al., and issued
Sep. 26, 1995 as U.S. Pat. No. 5,453,494; [0059] U.S. patent
application Ser. No. 07/918,141 filed Jul. 22, 1992 in the names of
Peter S. Kirlin, et al., and issued Jan. 18, 1994 as U.S. Pat. No.
5,280,012; [0060] U.S. application Ser. No. 07/615,303 filed Nov.
19, 1990; [0061] U.S. patent application Ser. No. 07/581,631 filed
Sep. 12, 1990 in the names of Peter S. Kirlin, et al., and issued
Jul. 6, 1993 as U.S. Pat. No. 5,225,561. [0062] U.S. patent
application Ser. No. 07/549,389 filed Jul. 6, 1990 in the names of
Peter S. Kirlin, et al. [0063] U.S. patent application Ser. No.
08/758,599 filed Nov. 27, 1996 in the names of Jeffrey F. Roeder,
et al., and issued Mar. 2, 1999 as U.S. Pat. No. 5,876,503.
[0064] The above-identified applications and patents variously
describe source reagent compositions, their synthesis and
formulation, as well as CVD techniques including, liquid delivery
chemical vapor deposition (LDCVD), and digital or atomic layer
chemical vapor deposition (ALCVD) and provide background and
assistive information with respect to the practice of the present
invention.
[0065] In general, the silicon precursor composition(s) and
method(s) of making such precursor composition(s) of the instant
invention may be formulated to comprise, consist of, or consist
essentially of any appropriate components herein disclosed, and
such silicon precursor compositions of the invention may
additionally, or alternatively, be formulated to be devoid, or
substantially free, of any components taught to be necessary in
prior art formulations that are not necessary to the achievement of
the objects and purposes of the invention hereunder.
[0066] The compositions of the present invention are useful in a
number of applications. For example, the compositions may be used
in the formation of silicon nitride barrier layers, low dielectric
constant thin films and gate dielectric thin films in a
semiconductor integrated circuit. To form such integrated circuits,
a semiconductor substrate may have a number of dielectric and
conductive layers formed on and/or within the substrate.
[0067] As used herein, the semiconductor substrate may include a
bare substrate or a substrate having any number of layers formed
thereon and the term "thin film" refers to a material layer having
a thickness of less than about 1000 microns.
[0068] In one embodiment, the present invention relates to a method
of synthesizing an aminosilane source reagent composition, by
reacting an aminosilane precursor compound with an amine source
reagent compound in a solvent medium comprising at least one
activating solvent component, to yield an aminosilane source
reagent composition having reduced halide content as compared to
the existing commercial precursors. Preferably the aminosilane
source reagent compound comprises less than 1000 ppm halide, more
preferably less than 500 ppm and most preferably less than 10 ppm
halide.
[0069] Aminosilane precursor compounds useful in the synthetic
process of the instant invention must have reactive leaving groups,
such as H and/or halogen. In one embodiment, aminosilane precursor
compounds useful in the instant invention include but are not
limited to, silicon halides, alkylsilanes and other aminosilanes.
Preferably, the aminosilane precursor compound is a silicon halide
compound comprising a composition selected from the group
consisting of: ##STR2## wherein R.sup.3 is selected from the group
consisting of hydrogen, C.sub.1-C.sub.4 alkyl, and C.sub.1-C.sub.4
alkoxy; x is from 0 to 3; Si is silicon; A is halogen; y is from 1
to 4; N is nitrogen; each of R.sup.1 and R.sup.2 is same or
different and is independently selected from the group consisting
of H; aryl, perfluoroaryl, C.sub.1-C.sub.8 alkyl, and
C.sub.1-C.sub.8 perfluoroalkyl; and n is from 1-6. Preferably, A is
Cl.
[0070] The amine source reagent compounds useful in the synthetic
process of the instant invention, include but are not limited to
amines having a composition selected from the group consisting of
##STR3## wherein B is selected from the group consisting of H, Li,
Na, K, Zn and MgBr; N is nitrogen; R.sup.1 and R.sup.2 are same or
different and each is independently selected from the group
consisting of H, aryl, perfluoroaryl, C.sub.1-C.sub.8 alkyl, and
C.sub.1-C.sub.8 perfluoroalkyl; and n is from 1-6. Preferably,
R.sup.1 and R.sup.2 are methyl and/or ethyl.
[0071] Activating solvent components useful in the present
invention include but are not limited to Lewis base compounds such
as ethers and amines. More specifically, ethereal solvents useful
in the present invention include but are not limited to, diethyl
ether, tetrahydrofuran (THF), ethylene glycol dimethyl ether
(glyme), diethylene glycol dimethyl ether (diglyme), 1,4-dioxane,
tetraethylene glycol dimethyl ether (tetraglyme),
1,4,7,10-tetraoxacyclododecane (12-Crown-4),
1,4,7,10,13-pentaoxacyclopentadecane (15-Crown-5), and
1,4,7,10,13,16-hexaoxacyclooctadecane (18-Crown-6); and amine
solvents useful in the present invention include but are not
limited to tertiary amines selected from the group consisting of,
pentamethyldiethylenetriamine (PMDETA), tetramethylethylene-diamine
(TMEDA), Triethylamine; (TEA), Diazabicycloun-decene (DBU),
Tri-n-butylamine (TNBA), and tetraethylethylenediamine (TEDA).
[0072] Many of the amine source reagent compounds useful in the
present invention exist as oligomers. The oligomer prevents
substitution of all reactive leaving groups (i.e., halides) on the
aminosilane precursor compound, since the oligomer is not as
soluble in many solvents and hence, not as reactive as its
corresponding monomer. However, in the presence of a polar
activating solvent, the oligomers are solvated into monomeric
species, thus providing the impetus for the amine-leaving group
substitution to occur.
[0073] Non-polar solvents useful in the present invention include
but are not limited to alkanes, alkenes, alkynes and aromatic
hydrocarbons.
[0074] In a further embodiment, the present invention relates to a
method of synthesizing an aminosilane source reagent composition,
comprising the steps of:
[0075] (1) combining an aminosilane precursor compound with an
amine source reagent compound in a solvent system comprising at
least one non-polar solvent, for a period of time sufficient to
provide for partial substitution of at least one halide on the
aminosilane precursor compound by an amine component, to produce a
reaction mixture comprising a partially substituted aminosilane
component and an unreacted amine component;
[0076] (2) removing the non-polar solvent from the reaction mixture
by vacuum evaporation;
[0077] (3) adding an activating polar solvent to the partially
substituted aminosilane component and the unreacted amine component
of the reaction mixture of step (1) to at least partially activate
the unreacted amine component;
[0078] (4) continuing the reaction of step (3) for a period of time
sufficient to provide for essentially stoichiometric substitution
of at least one halide on the aminosilane precursor compound by an
amine component.
[0079] In one embodiment, the present invention relates to a method
of synthesizing an aminosilane source reagent composition, by
reacting an aminosilane precursor compound with an amine source
reagent compound in a solvent system comprising at least one
activating solvent component in an amount equal to at least one
equivalent of the amine source reagent compound, to yield an
aminosilane precursor having reduced halide content as compared to
existing commercial precursors.
[0080] In a preferred embodiment of the synthetic method of the
instant invention, the aminosilane precursor compound is combined
with an amount of the amine source reagent compound that is in
excess of at least one equivalent of the amine source reagent
compound as shown in the following non limiting generic example:
SiCl.sub.4+5
LiNR.sub.2.fwdarw.Si(NR.sub.2).sub.4+4LiCl+LiNR.sub.2
[0081] The synthetic method of the instant invention, is not
limited to the specific examples disclosed herein, but rather
includes any combination of solvents in any order with the
requirement that at least one solvent component comprise a polar
activating component.
[0082] In a further embodiment, an aminosilane source reagent
composition is formed by a synthetic process comprising the
steps:
[0083] (1) combining an aminosilane precursor compound (e.g.
SiCl.sub.4) with excess amine source reagent compound that is equal
to at least one molar equivalent of the amine source reagent
compound (e.g., 5LiNR.sub.2), in a solvent system comprising at
least one non-polar solvent, such as hexanes, for a period of time
sufficient to provide for partial substitution of at least one
reactive leaving group on the aminosilane precursor compound, to
produce a reaction mixture comprising a partially substituted
aminosilane component and an unreacted amine component;
[0084] (2) removing the non-polar solvent from the reaction mixture
by vacuum evaporation;
[0085] (3) adding a polar solvent, such as tetraglyme, to the
partially substituted aminosilane component and the unreacted amine
component of the reaction mixture of step (1) to at least partially
activate the unreacted amine component;
[0086] (4) continuing the reaction of step (3) for a period of time
sufficient to provide for essentially stoichiometric substitution
of all reactive leaving groups on the silicon halide source reagent
compound by an amine component.
[0087] The period of time required for reactions to complete and
the temperature at which they are run, are parameters readily
determined by those skilled in the art. Such determinations are
based on parameters such as pressure, concentration, mixing speed
etc.
[0088] In one embodiment, the reaction mixture of step (1) as
outlined hereinabove, wherein the aminosilane precursor compound is
combined with the amine source reagent compound, should be carried
out at a temperature that is in the range of from about -30.degree.
C. to room temperature and a pressure that is about one atmospheric
pressure. Preferably the combination of the compounds is carried
out at a temperature of .+-.0.degree. C. and a pressure that is
about one atm.
[0089] In a further embodiment, the reaction mixture of step (3) as
outlined hereinabove, wherein the aminosilane precursor compound
having partially substituted leaving groups, is combined with the
amine source reagent compound, and the polar activating solvent,
should be carried out at a temperature that is in the range of from
about 0.degree. C. to 100.degree. C. at ambient pressure.
Preferably the reaction of step (3) is carried out a temperature
that is .+-.60.degree. C. at an ambient pressure.
[0090] The aminosilane source reagent compositions synthesized in
the aforementioned procedures, are crude product and must be
isolated and purified. Such isolation and purification methods are
readily available and known to those skilled in the instant art.
Preferably the crude aminosilane source reagent composition is
separated from the by-product by filtration or decantation and
preferably the separated aminosilane source reagent composition is
further purified by distillation to produce an aminosilane source
reagent composition having a halogen level of less than 1000 ppm,
preferably less than 500 ppm and most preferably less than 10
ppm.
[0091] The aminosilane source reagent compositions of the present
invention, when utilized in a CVD process to deposit silicon
containing thin films on a substrate, result in silicon containing
thin films having very little or no halide impurity.
[0092] In one embodiment, the present invention relates to silicon
precursors made by reacting an aminosilane precursor compound with
an amine source reagent compound in a solvent medium comprising at
least one activating solvent component, to yield an aminosilane
source reagent composition having a halogen content that is less
than 1000 ppm, said aminosilane source reagent composition selected
from the group consisting of: ##STR4## wherein R.sup.3 is selected
from the group consisting of hydrogen, C.sub.1-C.sub.4 alkyl, and
C.sub.1-C.sub.4 alkoxy; x is from 0 to 3; Si is silicon; A is
halogen; Y is from 0 to 3; N is nitrogen; each of R.sup.1 and
R.sup.2 is same or different and is independently selected from the
group consisting of H, aryl, perfluoroaryl, C.sub.1-C.sub.8 alkyl,
and C.sub.1-C.sub.8 perfluoroalkyl; and n is from 1-6.
[0093] In a further embodiment, the present invention relates to
novel, stable aminosilane source reagent compositions having
formula: R.sup.3.sub.xSiA.sub.y(NR.sup.1R.sup.2).sub.4-x-y wherein
R.sup.3 is selected from the group consisting of hydrogen,
C.sub.1-C.sub.4 alkyl, and C.sub.1-C.sub.4 alkoxy; x is from 0 to
3, A is Cl, y is from 0 to 3; R.sup.1 is methyl; and R.sup.2is
ethyl.
[0094] In a preferred embodiment, the aminosilane source reagent
compounds useful for depositing a silicon containing thin film on a
substrate include but are not limited to: Si(NMe.sub.2).sub.3Cl,
Si(NEt.sub.2).sub.2Cl.sub.2, Si(NMe.sub.2).sub.4,
Si(NEt.sub.2).sub.4 and Si(NMeEt).sub.4, HSi(NEt.sub.2).sub.3,
HSi(NEtMe).sub.3.
[0095] The invention in one embodiment relates to a CVD precursor
for forming a silicon containing thin film on a substrate, such
precursor composition including at least one aminosilane source
reagent composition.
[0096] The aminosilane source reagent compositions of the instant
invention are useful for producing silicon containing thin films,
including but not limited to silicon nitride thin films, SiO.sub.2
dielectric thin films, doped SiO.sub.2 dielectric thin films, low
dielectric constant thin films and metal silicon-oxy-nitride thin
films.
[0097] In one embodiment, the silicon precursor composition of the
instant invention is used in combination with a dopant precursor to
deposit a doped dielectric SiO.sub.2 thin film. Preferably the
dopant precursor comprises a metalloamide source reagent
composition.
[0098] In a still further embodiment, the instant invention relates
to a silicon precursor composition used in combination with a
dopant precursor to deposit a metal silicate thin film, wherein the
silicon precursor is an aminosilane source reagent composition
selected from the group consisting of ##STR5## wherein R.sup.3 is
selected from the group consisting of hydrogen, C.sub.1-C.sub.4
alkyl, and C.sub.1-C.sub.4 alkoxy; x is from 0 to 3; Si is silicon;
A is halogen; Y is from 0 to 3; N is nitrogen; each of R.sup.1 and
R.sup.2 is same or different and is independently selected from the
group consisting of H, aryl, perfluoroaryl, C.sub.1-C.sub.8 alkyl,
and C.sub.1-C.sub.8 perfluoroalkyl; and n is from 1-6; and
[0099] the dopant precursor is a metalloamide source reagent
composition selected from the group consisting of: ##STR6##
wherein, M is selected from the group consisting of: Zr, Hf. Y, La,
Lanthanide series elements, Ta, Ti, Al; N is nitrogen; each of
R.sup.1 and R.sup.2is same or different and is independently
selected from the group consisting of H, aryl, perfluoroaryl,
C.sub.1-C.sub.8 alkyl, C.sub.1-C.sub.8 perfluoroalkyl, alkylsilyl;
x is the oxidation state on metal M; and n is from 1-6.
[0100] In a preferred embodiment, M is Zr or Hf; and R.sup.1 and
R.sup.2 are methyl and/or ethyl. In a more preferred embodiment,
the metalloamide source reagents useful for depositing dielectric
thin films on a substrate include but are not limited to, compounds
of the formula M(NMe.sub.2).sub.x, M(NEt.sub.2).sub.x,
M(NMeEt).sub.x
[0101] Examples of metalloamide source reagent compositions, which
may be usefully employed in the present invention include, without
limitation, Zr(NMe.sub.2).sub.4, Zr(NMeEt).sub.4,
Zr(NEt.sub.2).sub.4, Ta(NEt.sub.2).sub.5, Ta(NMe.sub.2).sub.5,
Ta(NMeEt).sub.5, Zr(NiPr.sub.2).sub.4,
Zr(NMe.sub.2).sub.2(NPr.sub.2).sub.2, Zr(NC.sub.6H.sub.12).sub.4,
Zr(NEt.sub.2).sub.2(NPr.sub.2).sub.2, Hf(NEt.sub.2).sub.4,
Hf(NMe.sub.2).sub.4, Hf(NMeEt).sub.4, La(NMe.sub.2).sub.3,
La(NEt.sub.2).sub.3, La(NMeEt).sub.3, Al(NMe.sub.2).sub.3,
Al(NEt.sub.2).sub.3, Y(NMe.sub.2).sub.3, Y(NEt.sub.2).sub.3,
Y(NMeEt).sub.3, Ti(NMe.sub.2).sub.4, Ti(NEt.sub.2).sub.4,
Ti(NMeEt).sub.4, Ta(NMe.sub.2).sub.5, Ta(NEt.sub.2).sub.5, wherein
Me represents methyl, Et represents ethyl, Pr represents propyl,
and iPr represents isopropyl. Preferred metalloamide source reagent
compounds useful in the present invention include
Zr(NMe.sub.2).sub.4, Zr(NEt.sub.2).sub.4, Hf(NEt.sub.2).sub.4 and
Hf(NMe.sub.2).sub.4.
[0102] In a specific embodiment, the metalloamide source reagent
compound useful in the present invention may comprise an oligomer,
i.e. Al.sub.2(.mu.-NMe.sub.2).sub.2(NMe.sub.2).sub.4.
[0103] In a further embodiment, the present invention relates to a
CVD precursor composition for forming a silicon containing thin
film on a substrate, said precursor composition made by reacting an
aminosilane precursor compound with an amine source reagent
compound in a solvent medium comprising at least one activating
solvent component, to yield an aminosilane source reagent
composition having a halogen content that is less than 1000 ppm,
said precursor composition including at least one aminosilane
source reagent composition selected from the group consisting of:
##STR7## wherein R.sup.3 is selected from the group consisting of
hydrogen, C.sub.1-C.sub.4 alkyl, and C.sub.1-C.sub.4 alkoxy; x is
from 0 to 3; Si is silicon; A is halogen; Y is from 0 to 3; N is
nitrogen; each of R.sup.1 and R.sup.2 is same or different and is
independently selected from the group consisting of H, aryl,
perfluoroaryl, C.sub.1-C.sub.8 alkyl, and C.sub.1-C.sub.8
perfluoroalkyl; and n is from 1-6.
[0104] In a still further embodiment, the present invention relates
to a CVD precursor composition for forming a silicon containing
thin film on a substrate, such precursor composition including at
least one aminosilane source reagent composition selected from the
group for forming a silicon containing thin film on a substrate;
and
[0105] at least one metalloamide source reagent composition
selected from the group consisting of: ##STR8## wherein M is
selected from the group consisting of: Zr, Hf, Y, La, Lanthanide
series elements, Ta, Ti, Al; N is nitrogen; each of R.sup.1 and
R.sup.2 is same or different and is independently selected from the
group consisting of H, aryl, perfluoroaryl, C.sub.1-C.sub.8 alkyl,
C.sub.1-C.sub.8 perfluoroalkyl, alkylsilyl; x is the oxidation
state on metal M; and n is from 1-6. Preferably, R.sup.1 and
R.sup.2 of the aminosilane and metalloamide source reagent
compositions are methyl and/or ethyl.
[0106] In one embodiment, the silicon CVD precursor composition of
the present invention is used to deposit a metal silicate gate
dielectric thin film wherein the silicon precursor is suitably used
in combination with at least one dopant precursor, to yield the
product metal silicate film. The dopant precursor may
advantageously comprise a metalloamide source reagent composition
as described herein or may alternatively comprise an alternative
dopant source reagent composition as known to those skilled in the
art, to deposit metal silicate thin films, (e.g. metal
beta-diketonates, metal alkoxides, and metal carboxylates).
[0107] By utilizing a precursor composition including at least one
aminosilane source reagent composition and at least one
metalloamide source reagent composition to produce a metal silicate
dielectric thin film on a substrate, with the metalloamide source
reagent composition containing at least part of the metal to be
incorporated in the product dielectric metal silicate film, and the
aminosilane source reagent compound containing at least part of the
silicon to be incorporated in the product dielectric metal silicate
film, it is possible by selection of the proportions of such
respective compounds to correspondingly vary the stoichiometric
composition (metalsilicon ratio) of the metal silicate dielectric
film, to obtain a desired character of structural and performance
properties in the product film. The relative proportions of the at
least one aminosilane source reagent composition and the
metalloamide source reagent composition relative to one another are
employed to controllably establish the desired M.sub.x/Si.sub.1-x
ratio in the deposited silicate thin films, wherein
M.sub.x/Si.sub.1-x is from about 0.01 to 10. The exact composition
will be a trade off between high Si films, which prevent
crystallization during subsequent high temperature processing, and
high M films, which have higher dielectric constant (lower
EOT).
[0108] In one embodiment, the silicon CVD precursor composition of
the present invention is used to deposit a silicon nitride barrier
layer, wherein the silicon precursor is suitably used in
combination with NH.sub.3, to yield the product silicon nitride
film. The CVD precursor composition may be used in combination with
silicon and/or nitrogen sources as readily known to those skilled
in the art, to deposit silicon nitride thin films, (e.g.,
ammonia).
[0109] In a further embodiment, the present invention relates to
stable solutions for chemical vapor deposition (CVD) of
silicon-containing thin films of varying types, including silicon
nitride, silicon dioxide and doped silicon dioxide films (when a
dopant co-precursor is utilized), wherein the stable solution
comprises at least one aminosilane source reagent composition and
at least one solvent component, in which the aminosilane source
reagent composition is soluble or suspendable. Accordingly, the
aminosilane source reagent composition and the at least one solvent
component are combined to produce a precursor solution mixture for
depositing a silicon containing thin film on the substrate.
[0110] In a further embodiment, the present invention relates to a
CVD multi-component, single source precursor composition useful for
forming a metal silicate dielectric thin film on a substrate, such
precursor composition including at least one aminosilane source
reagent composition as described hereinabove, at least one
metalloamide source reagent composition as described hereinabove
and a solvent medium in which the aminosilane source reagent
composition and the metalloamide source reagent composition are
soluble or suspendable, wherein the aminosilane source reagent
composition, the metalloamide source reagent composition, and the
solvent medium are combined to produce a chemically compatible,
single source solution mixture for depositing a silicon containing
dielectric thin film on the substrate.
[0111] Providing a precursor composition in liquid (i.e., neat
solution or suspension) form facilitates rapid volatilization
(i.e., flash vaporization) of the source reagent composition and
transport of the resultant precursor vapor to a deposition locus
such as a CVD reaction chamber. The aminosilane and metalloamide
source reagent compositions of the present invention are chosen to
provide a degenerate sweep of ligands, to eliminate ligand exchange
and to provide a robust precursor delivery, gas-phase transport and
CVD process.
[0112] The precursor compositions of the present invention may
comprise any suitable solvent medium that is compatible with the
aminosilane and optionally the metalloamide source reagent
compositions contained therein. The solvent medium in such respect
may comprise a single solvent component, or alternatively a mixture
of solvent components. Illustrative solvent media that may be
variously usefully employed include ethers, glymes, tetraglymes,
amines, polyamines, aliphatic hydrocarbon solvents, aromatic
hydrocarbon solvents, cyclic ethers, and compatible combinations of
two or more of the foregoing. A particularly preferred solvent
species useful in the practice of the present invention is octane.
The percentage of the precursor in the solution may range from 0.1
to 99.99% by weight, based on the total weight of the solution.
[0113] The silicon precursor compositions of the invention may be
deposited on a wafer or other substrate by use of a CVD system,
such systems being well known in the semiconductor fabrication art.
Preferred CVD systems include low-pressure CVD systems.
[0114] In a further embodiment the present invention relates to a
method for forming a silicon containing thin film on a substrate by
chemical vapor deposition, such method including the steps of:
[0115] (1) vaporizing a precursor composition comprising at least
one aminosilane source reagent composition made by reacting an
aminosilane precursor compound with an amine source reagent
compound in a solvent medium comprising at least one activating
solvent component, to yield an aminosilane source reagent
composition having a halogen content that is less than 1000 ppm,
wherein said aminosilane source reagent composition is selected
from the group consisting of: ##STR9## wherein R.sup.3 is selected
from the group consisting of hydrogen, C.sub.1-C.sub.4 alkyl, and
C.sub.1-C.sub.4 alkoxy; x is from 0 to 3; Si is silicon; A is
halogen; Y is from 0 to 3; N is nitrogen; each of R.sup.1 and
R.sup.2 is same or different and is independently selected from the
group consisting of H, aryl, perfluoroaryl, C.sub.1-C.sub.8 alkyl,
and C.sub.1-C.sub.8 perfluoroalkyl; and n is from 1-6;
[0116] (2) transporting such precursor vapor into a chemical vapor
deposition zone containing a substrate, optionally using a carrier
gas to effect such transport;
[0117] contacting the precursor vapor with a substrate in such
chemical vapor deposition zone, at elevated temperature to deposit
a corresponding silicon containing thin film.
[0118] A wide variety of CVD process conditions may be utilized for
chemical vapor deposition employing the compositions of the present
invention. Typical liquid delivery MOCVD process conditions may
include substrate temperature ranges of 160-300.degree. C., with
about 170.degree. C. to about 250.degree. C. being more typical;
vaporizer temperature ranges may be from about 50.degree. C. to
about 150.degree. C., with about 60.degree. C. to about 100.degree.
C. being more typical; pressure ranges are generally from about
0.05 to about 20 Torr (and most preferably from about 0.1 to about
5 Torr), with a range of about 0.2 to about 0.5 Torr being more
typical; and inert gas flows of helium or argon of from about
25-750 sccm (and most preferably from about 50 to about 200 sccm),
at a temperature approximately the same as the vaporizer. In some
cases, a co-reactant may be introduced (i.e., water, alcohol or
hydrogen forming gas) to facilitate the film growth process.
[0119] The compositions of the present invention are not limited in
respect of their use with the aforementioned low-pressure CVD
deposition tools, however, and other CVD tools, for example PECVD
tools, or other deposition tools, may be utilized.
[0120] In one embodiment the aminosilane source reagent
compositions of the instant invention may used in an atomic layer
chemical vapor deposition method, wherein the aminosilane source
reagent composition is vaporized and introduced into a chemical
vapor deposition chamber comprising a substrate, in a sequential or
"pulsed" deposition mode, during which time, extremely co-reactive
gases may be employed, such as ozone, water vapor or reactive
alcohols, that might normally be expected to produce deleterious
deposition effects on the CVD process (i.e., gas phase particle
formation).
[0121] In a further embodiment, the atomic layer chemical vapor
deposition method of the present invention, may further comprise a
metalloamide precursor vapor that may be simultaneously co-pulsed
and co-deposited with the silicon precursor vapor, on a substrate.
Alternatively, the aminosilane precursor vapor may be deposited on
a substrate in a sequential pulsing method, wherein the aminosilane
compound alternates pulses with the metalloamide compound. The
dielectric thin films are built up by introducing short bursts of
gases in cycles.
[0122] In a further embodiment, a co-reactant may be used in a
pulsed or atomic layer chemical vapor deposition method, wherein
the metalloamide precursor and/or aminosilane precursor vapor is
separated from the co-reactant by time in the pulse track. The
co-reactant may be utilized to facilitate the decomposition of the
precursor on a substrate, within a desired temperature regime and
to produce carbon-free dielectric thin-films. As an example, the
use of water vapor may be utilized to induce a lower decomposition
temperature of the aminosilane precursor vapor, which in some
instances has been found to be stable in oxidizing environments
such as N.sub.2O.
[0123] The specific nature of the pulse track and number of cycles
may be varied. In a typical ALCVD process, a cycle lasts from 1-5
seconds. The following non-limiting examples demonstrate various
pulse tracks defining precursor(s) and co-reactant(s) that may be
successfully used to deposit the dielectric thin films of the
present invention:
[0124] example track 1-(metalloamide/purge
(inert)/co-reactant+N.sub.2O/purge (inert))n cycles;
[0125] example track 2-(metalloamide+aminosilane/purge
(inert)/N.sub.2O/purge (inert))n cycles;
[0126] example track 3-(metalloamide+co-reactant
N.sub.2O/co-reactant water vapor/purge (inert))n cycles;
[0127] example track 4-(metalloamide+co-reactant
N.sub.2O/aminosilane/co-reactant water vapor/purge (inert))n
cycles.
[0128] wherein n is an integer number, typically ranging from 10 to
100, and different co-reactants have different oxidizing
potentials.
[0129] The compositions of the present invention may be delivered
to the CVD reactor in a variety of ways. For example, a liquid
delivery system may be utilized. Such systems generally include the
use of liquid MFCs (mass flow controllers). An exemplary liquid
delivery system that may be used is the ATMI Sparta 150 Liquid
Delivery System (commercially available from ATMI, Inc., Danbury,
Conn.).
[0130] Liquid delivery systems generally meter a desired flow rate
of the precursor composition in liquid form to the CVD process
tool. At the process tool chamber, or upstream thereof, the liquid
may be vaporized through use of a vaporizer. Such vaporizers may
utilize thermal heating, acoustics, ultrasound and high flow
nebulizers. Further descriptions of liquid delivery systems are
contained in U.S. Pat. Nos. 5,204,314; 5,362,328; 5,536,323; and
5,711,816, the disclosures of which are hereby expressly
incorporated herein by reference in their entireties.
[0131] In the practice of the present invention utilizing liquid
delivery, the silicon precursor species, if of solid or liquid form
at ambient conditions, may be dissolved or suspended in a
compatible solvent medium as more fully described in U.S. Pat. No.
5,820,664 issued Oct. 13, 1998 for "Precursor Compositions For
Chemical Vapor Deposition, And Ligand Exchange Resistant
Metal-Organic Precursor Solutions Comprising Same," the disclosure
of which is hereby incorporated herein in its entirety by
reference.
[0132] The precursors of the present invention may be deposited
using any chemical vapor deposition system known in the art. A
preferred liquid delivery MOCVD System is described in U.S. Pat.
No. 5,204,314, issued Apr. 20, 1993, for "Method for Delivering an
Involatile Reagent in Vapor Form to a CVD Reactor," the disclosure
of which is hereby incorporated herein in its entirety by
reference.
[0133] In liquid delivery CVD, the source liquid may comprise the
source reagent compound(s) if the compound or complex is in the
liquid phase at ambient temperature (e.g., room temperature,
25.degree. C.) or other supply temperature from which the source
reagent is rapidly heated and vaporized to form precursor vapor for
the CVD process. Alternatively, if the source reagent compound or
complex is a solid at ambient or the supply temperature, such
compound or complex can be dissolved or suspended in a compatible
solvent medium therefore to provide a liquid phase composition that
can be submitted to the rapid heating and vaporization to form
precursor vapor for the CVD process. The precursor vapor resulting
from the vaporization then is transported, optionally in
combination with a carrier gas (e.g., He, Ar, H.sub.2, O.sub.2,
etc.), to the chemical vapor deposition reactor where the vapor is
contacted with a substrate at elevated temperature to deposit
material from the vapor phase onto the substrate or semiconductor
device precursor structure positioned in the CVD reactor.
[0134] The precursor liquid may be vaporized in any suitable manner
and with any suitable vaporization means to form corresponding
precursor vapor for contacting with the elevated temperature
substrate on which the dielectric film is to be formed. The
vaporization may for example be carried out with a liquid delivery
vaporizer unit of a type as commercially available from Advanced
Technology Materials, Inc. (Danbury, Conn.) under the trademark
SPARTA and VAPORSOURCE II, in which precursor liquid is discharged
onto a heated vaporization element, such as a porous sintered metal
surface, and flash vaporized. The vaporizer may be arranged to
receive a carrier gas such as argon, helium, etc. and an
oxygen-containing gas may be introduced as necessary to form the
dielectric thin film. The precursor vapor thus is flowed to the
chemical vapor deposition chamber and contacted with the substrate
on which the dielectric film is to be deposited. The substrate is
maintained at a suitable elevated temperature during the deposition
operation by heating means such as a radiant heating assembly, a
susceptor containing a resistance heating element, microwave heat
generator, etc. Appropriate process conditions of temperature,
pressure, flow rates and concentration (partial pressures) of metal
and silicon components are maintained for sufficient time to form
the dielectric film at the desired film thickness, (i.e., in a
range of from about 2 nanometers to about 1000 micrometers), and
with appropriate dielectric film characteristics.
[0135] The step of vaporizing the source reagent compounds of the
present invention is preferably carried out at a vaporization
temperature in the range of from about 50.degree. C. to about
300.degree. C. Within this narrow range of vaporization
temperature, the metalloamide and aminosilane source reagent
compounds are effectively vaporized with a minimum extent of
premature decomposition.
[0136] In the optional use of a carrier gas in the practice of the
present invention, for transporting the vaporized source reagent
composition into the chemical vapor deposition zone, suitable
carrier gas species include gases that do not adversely affect the
dielectric film being formed on the substrate. Preferred gases
include argon, helium, krypton or other inert gas, with argon gas
generally being most preferred. In one illustrative embodiment,
argon gas may be introduced for mixing with the vaporized source
reagent composition at a flow rate of about 100 standard cubic
centimeters per minute (sccm).
[0137] Oxidizing gases useful for the broad practice of the present
invention include, but are not limited to, O.sub.2, N.sub.2O, NO,
H.sub.2O and O.sub.3, More preferably, the oxidizer used comprises
N.sub.2O.
[0138] The deposition of the silicon containing thin films of the
present invention are preferably carried out under an elevated
deposition temperature in a range of from about 250.degree. C. to
about 750.degree. C.
[0139] The use of the compositions disclosed herein is not limited
to liquid delivery systems, and any method, which adequately
delivers the composition to the process tool is. satisfactory.
Thus, for example, bubbler-based delivery systems may be utilized,
but are not preferred. In such systems, an inert carrier gas is
bubbled through the precursor composition (typically in liquid form
above its melting point). The resulting gas, which is wholly or
partially saturated with the vapor of the composition, is provided
to the CVD tool.
[0140] Here and throughout this disclosure, where the invention
provides that at least one aminosilane source reagent composition
is present in a composition or method, the composition or method
may contain or involve additional aminosilane and/or other
compounds.
EXAMPLES
Experiment 1
[0141] Silica films were grown with the silicon precursors listed
in Table I, Si(NMe.sub.2).sub.3Cl and Si(NEt.sub.2).sub.2Cl.sub.2.
Precursor solutions were prepared at 0.1M Si in octane. Substrates
of (100) Si were prepared with an SCl treatment followed by dilute
HF to remove any native SiO.sub.2. The generic process conditions
for the experiments are shown in Table II. Results from the growth
of hafnia films encouraged the inventors to center initial
experiments on growth in an N.sub.2O atmosphere although growth in
O.sub.2 or other oxidizer could be used at temperatures at or below
500.degree. C. A limited pressure-temperature matrix was performed
for each Si precursor using the N.sub.2O ambient as shown in FIGS.
2A and 2B. TABLE-US-00001 TABLE I Precursors used for film
deposition. (Bis(diethyl-amino)dichlorosilane)
Si(N(C.sub.2H.sub.5).sub.2).sub.2Cl.sub.2
(Tris(dimethyl-amino)chlorosilane) Si(N(CH.sub.3).sub.2).sub.3Cl
Tetrakis(diethyl-amino)hafnium Hf(N(C.sub.2H.sub.5).sub.2).sub.4
TDEAHf Tetrakis(dimethyl-amino)hafnium Hf(N(CH.sub.3).sub.2).sub.4
TDMAHf
[0142] TABLE-US-00002 TABLE II Generic process conditions Precursor
solution 0.10 M in octane Precursor solution delivery rate 0.10
ml/min Vaporization Temperature 150.degree. C. Run time 10 minutes
Carrier gas 100 sccm Ar Heating and Cooling process gas 500 sccm Ar
Run time process gas 400 sccm N.sub.2O Pressure 0.8, 2.2, or 8.0
Torr Temperature 400-650.degree. C. wafer surface
[0143] From NMR studies of precursor compatibility, it was shown
that Si(NEt.sub.2).sub.2Cl.sub.2 is compatible with TDEAHf in
solution, with any ligand exchange being degenerate.
Si(NMe.sub.2).sub.3Cl is compatible with both TDEAHf and TDMAHf. A
solution of 0.05M TDEAHf: 0.05M Si(NEt.sub.2).sub.2Cl.sub.2 was
produced by mixing the two 0.1M solutions. This mixture was used to
grow films over the entire matrix of process conditions.
[0144] Film thickness was measured using single-wavelength
ellipsometry at 70.degree. incidence angle, and XRF. For SiO.sub.2
deposition, all films were less than 30 .ANG. thick, so an index of
refraction could not be measured accurately. Film thickness was
assigned based on an assumed index of refraction, n=1.46, typical
of high quality thermal oxide. For HfO.sub.2, the XRF was
calibrated by assuming the X-ray efficiencies were equivalent to
TaO.sub.2.5, for which standards that been measured by RBS. The
Hf:Si composition was estimated by assuming that both are fully
oxidized and fully dense. The ellipsometric thickness not accounted
for by HfO.sub.2 was assigned to SiO.sub.2, and composition was
calculated from these two thicknesses.
Results
[0145] Growth rates of SiO.sub.2 were less than 3 .ANG./min under
all conditions as shown in FIG. 3 and FIG. 4. There is some
indication that the Si(NEt.sub.2).sub.2Cl.sub.2 may form silica
films a little bit more readily, however, none of the growth rates
are sufficient for the two precursors under the instant
conditions.
[0146] The growth of SiO.sub.2 with only the TDEAHf, as measured by
the subtraction of ellipsometric thickness from XRF thickness
(shown in FIG. 5) was greater than that from the
Si(NEt.sub.2).sub.2Cl.sub.2 precursor alone (FIG. 3) Films grown
from the precursor mixture (TDEAHf+Si(NEt.sub.2).sub.2Cl.sub.2)
showed still higher SiO.sub.2 growth rates as shown in FIG. 6. This
increased growth rate compared to FIG. 3 is unexpected and should
be quite useful for the growth of hafnium silicate films of uniform
Hf:Si composition through the thickness of the film.
[0147] The films have a mixed Si:Hf composition on the film
surface. The constant SiO.sub.2 growth rate over the range of
500-600.degree. C. at 2.2 Torr being the same as 0.8 Torr at
600.degree. C. is taken as evidence of mass transport limited
deposition over the range of the process. The addition of water
vapor or O.sub.2, should further decrease the temperature window
wherein both Hf and Si alkylamido precursors transport and
decompose reliably.
Experiment 2 Prior Art Synthetic Process
[0148] When attempts were made to synthesize Si(NR.sub.2).sub.4
R=Et and Me by combining SiCl.sub.4 in hexanes with 5 equivalents
of LiNR.sub.2, only CISi(NMe.sub.2).sub.3 and
Cl.sub.2Si(NEt.sub.2).sub.2 were obtained.
Experiment 3 Synthesis of Tetrakis(Dialkylamino) Silanes
[0149] SiCl.sub.4 reacts with 5 equivalents of LiNR.sub.2 initially
in a non-polar solvent, such as hexanes. Then the non-polar solvent
is pumped off completely under vacuum. Polar solvent is added into
the reaction vessel to continue the reaction. The resulting slurry
in polar solvent is refluxed for 4-8 hours to facilitate the
completion of the reaction.
Experiment 4 Synthesis of Tetrakis (Dimethylamino) Silane
[0150] The general reactions were carried out under a steady flow
of nitrogen. A 5L Schlenk flask was charged with 0.8L of 1.6M
solution of n-BuLi in hexane, 1L of anhydrous hexane and a big
magnetic stirring bar. Then 60 g (10% excess) of HNMe.sub.2 was
bubbled into the Schlenk flask slowly at 0.degree. C., under
magnetic stirring. During the addition, very fine white precipitate
of LiNMe.sub.2 was formed and the reaction mixture became extremely
viscous. The mixture was allowed to reach room temperature and then
was stirred for an additional 2 h. A solution of SiCl.sub.4 (43.5
g, 29.3 mL) in hexane (50 mL) was slowly added to the reaction
flask. Moderate heat was generated (exothermic) and the external
cooling to 0.degree. C. was applied. Upon completion of SiCl.sub.4
addition, the mixture became less viscous. The mixture was allowed
to reach room temperature and then was stirred for an additional 2
h. All volatiles were removed in vacuum. Then the reaction flask
was charge with 0.5 L of anhydrous THF. The resulting mixture was
refluxed for 4 h. THF was removed in vacuum to give a slurry-like
mixture of Si(NMe.sub.2).sub.4 and Li salts. 400 mL of hexane were
added to extract Si(NMe.sub.2).sub.4 and the resulting mixture was
filtered. A second extraction was applied with 100 mL of hexane and
a slightly yellow filtrate was obtained. Removal of volatiles under
vacuum followed by the vacuum distillation (35.degree. C. at 1
mmHg) gave 31.3 grams of colorless liquid. Yield: 60%. Bp.
35.degree. C. at 1 mmHg. Anal. (calcd., %): C 47.16 (47.06), H
11.42 (11.76), N 26.73 (27.45). Mass spectrum (EI, %): m/z 204
(M.sup.+, 70), 160 (M.sup.+-NMe.sub.2, 100), 116 (M.sup.+-2
NMe.sub.2, 90). FIG. 7 .sup.1H NMR (C.sub.6D.sub.6): .quadrature.
2.51 (s, CH.sub.3). Residual Cl content is less than 10 ppm
(detection limit of analysis).
Experiment 4 Synthesis of Tetrakis (Ethylmethylamino) Silane
[0151] A SL Schlenk flask was charged with 0.8L of 1.6M solution of
n-BuLi in hexane, 1 L of anhydrous hexane and a big magnetic
stirring bar. The reaction mixture was maintained at 0.degree. C.
during the addition of HNEtMe (79.3 g, 1.344 mol, 5% excess)
solution in hexane (100 mL). Very fine white precipitate of LiNEtMe
formed immediately and the reaction mixture became extremely
viscous. The mixture was allowed to reach room temperature and then
was stirred for an additional hour. A solution of HSiCl.sub.3
(43.36 g, 0.32 mol) in hexane (100 mL) was slowly added to the
reaction flask. Moderate heat was generated (exothermic) and the
external cooling to 0.degree. C. was applied. Upon completion of
HSiCl.sub.3 addition, the mixture became less viscous. The mixture
was allowed to reach room temperature and then was stirred for an
additional hour. All volatiles were removed in vacuum. Then the
reaction flask was charge with 0.5 L of anhydrous THF. The
resulting mixture was refluxed for 4 h. THF was removed in vacuum.
300 mL of hexane were added to extract amidosilanes, the resulting
mixture was filtered, and the precipitate was discarded. Removal of
volatiles under vacuum followed by the vacuum distillation gave two
fractions (28.degree. C. at 0.5 mmHg and 50.degree. C. at 0.3 mmHg)
in 4:3 molar rations. The first fraction was confirmed to be
HSi(NEtMe).sub.3. The second fraction was identified as
Si(NEtMe).sub.4. Yield: 30%. Bp. 50.degree. C. at 0.3 mmHg. Anal.
(calcd., %): C 55.61 (55.38), H 12.58 (12.31), N 21.08 (21.54).
Mass spectrum (EI, %): m/z 260 (M.sup.+, 40), 202 (M.sup.+-NEtMe,
70), 144 (M.sup.+-2 NEtMe, 50), 86 (M.sup.+-3 NEtMe, 100). .sup.1H
NMR (C.sub.6D.sub.6): .quadrature. 2.83 (8H, q, J(H--H)=7 Hz,
CH.sub.2CH.sub.3), 2.51 (12H, s, CH.sub.3), 1.07 (12H, t, J(H--H)=7
Hz, CH.sub.2CH). .sup.13C NMR: (C.sub.6D.sub.6) .quadrature. 44.68
(CH.sub.2--CH.sub.3), 35.07 (CH.sub.3), 15.01
(CH.sub.2--CH.sub.3).
[0152] The features, aspects and advantages of the present
invention are further shown with reference to the following
non-limiting examples relating to the invention.
* * * * *