U.S. patent application number 13/036602 was filed with the patent office on 2011-07-28 for precursors for deposition of metal oxide layers or films.
This patent application is currently assigned to SIGMA-ALDRICH CO.. Invention is credited to Anthony Copeland Jones.
Application Number | 20110184156 13/036602 |
Document ID | / |
Family ID | 32180214 |
Filed Date | 2011-07-28 |
United States Patent
Application |
20110184156 |
Kind Code |
A1 |
Jones; Anthony Copeland |
July 28, 2011 |
PRECURSORS FOR DEPOSITION OF METAL OXIDE LAYERS OR FILMS
Abstract
Rare earth metal precursors, for use in MOCVD techniques have a
ligand of the general formula OCR.sup.1(R.sup.2)CH.sub.2X, wherein
R.sup.1 is H or an alkyl group, R.sup.2 is an optionally
substituted alkyl group and X is selected from OR and NR.sub.2,
wherein R is an alkyl group or a substituted alkyl group. Methods
of making such precursors and methods of depositing metal oxide
layers from such precursors are also described.
Inventors: |
Jones; Anthony Copeland;
(Eccleston Park, GB) |
Assignee: |
SIGMA-ALDRICH CO.
St. Louis
DE
|
Family ID: |
32180214 |
Appl. No.: |
13/036602 |
Filed: |
April 12, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10548946 |
Aug 29, 2006 |
7927661 |
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PCT/GB2004/001047 |
Mar 11, 2004 |
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13036602 |
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Current U.S.
Class: |
534/15 |
Current CPC
Class: |
C07F 5/003 20130101;
C23C 16/40 20130101 |
Class at
Publication: |
534/15 |
International
Class: |
C07F 5/00 20060101
C07F005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 17, 2003 |
GB |
0306027.4 |
Sep 12, 2003 |
GB |
0321409.5 |
Nov 1, 2003 |
GB |
0325752.4 |
Claims
1. Rare earth metal precursors, for use in MOCVD techniques having
a ligand of the general formula OCR.sup.1(R.sup.2)CH.sub.2X,
wherein R.sup.1 is H or an alkyl group, R.sup.2 is an optionally
substituted alkyl group and X is selected from OR and NR.sub.2,
wherein R is an alkyl group or a substituted alkyl group.
2. A precursor as claimed in claim 1 having the following general
formula: M[OCR.sup.1(R.sup.2)(CH.sub.2).sub.nX].sub.3 wherein M is
a rare earth metal R.sup.1 is H or an alkyl group, R.sup.2 is an
optionally substituted alkyl group and X is selected from OR and
NR.sub.2, wherein R is an alkyl group or a substituted alkyl group,
n=1 to 4.
3. A precursor as claimed in claim 1 or 2, wherein M is
praseodymium.
4. A precursor as claimed in any one of claims 1 to 3, wherein the
ligand of the formula OCR.sup.1(R.sup.2)(CH.sub.2).sub.nX is
1-methoxy-2-methyl-2-propanolate (mmp) [OCMe.sub.2CH.sub.2OMe].
5. A precursor as claimed in claim 1 or 2, wherein the ligand is
chosen from the group of OCH(Me)CH.sub.2OMe, OCEt.sub.2CH.sub.2OMe,
OCH(Et)CH.sub.2OMe, OC(Pr.sup.i).sub.2CH.sub.2OMe,
OCH(Pr.sup.i)CH.sub.2OMe, OC(Bu.sup.t).sub.2CH.sub.2OMe,
OCH(Bu.sup.t)CH.sub.2OMe, OCH(Bu.sup.t)CH.sub.2OEt,
OC(Bu.sup.t).sub.2CH.sub.2OEt, OC(Pr.sup.i).sub.2CH.sub.2OEt,
OCH(Bu.sup.t)CH.sub.2NEt.sub.2,
OC(Pr.sup.i).sub.2CH.sub.2OC.sub.2H.sub.4OMe and
OC(Bu.sup.t)(CH.sub.2OPr.sup.i).sub.2.
6. Pr(mmp).sub.3.
7. La(mmp).sub.3.
8. Gd(mmp).sub.3.
9. Nd(mmp).sub.3.
10. A method of making rare earth metal oxide precursors for use in
MOCVD techniques comprising reacting a ligand
HOCR.sup.1(R.sup.2)(CH.sub.2).sub.nX, wherein R.sup.1 is H or an
alkyl group, R.sup.2 is an optionally substituted alkyl group and X
is selected from OR and NR.sub.2, wherein R is an alkyl group or a
substituted alkyl group, n=1 to 4, with the corresponding rare
earth metal alkylamide M(NR.sub.2).sub.3 or silylamide precursor
M(N(SiR.sub.3).sub.2).sub.3 precursor,
Pr{N(SiMe.sub.3).sub.2}.sub.3, wherein R=alkyl, in appropriate
molar proportions.
11. A method as claimed in claim 10, wherein the ligand is
mmpH.
12. A method as claimed in claim 10 or 11, wherein the rare earth
metal compound is praseodymium. silylamide.
13. A method as claimed in claim 10 or 11, wherein in the rare
earth metal alkylamide or silylamide R is selected from Me, Et and
Pr.sup.i.
14. A method of making lanthanide and rare earth element complexes
of the formula M[OCR.sup.1(R.sup.2)CH.sub.2X].sub.3, wherein
R.sup.1 is H or an alkyl group, R.sup.2 is an optionally
substituted alkyl group and X is selected from OR and NR.sub.2,
wherein R is an alkyl group or a substituted alkyl group and n=1 to
4, comprising the salt exchange reaction of
M(NO.sub.3).sub.3(tetraglyme) with an akali metal or alkaline earth
metal salt of [OCR.sup.1(R.sup.2)CH.sub.2X].sub.3 (mmp) in
tetrahydrofuran solvent.
15. A method as claimed in claim 14, wherein the alkali metal salt
is Na(mmp).
16. A method as claimed in claim 14 or 15, wherein the rare earth
metal complex prepared is selected from Sc(mmp).sub.3, Y(mmp).sub.3
and Ln(mmp).sub.a.
17. A method of depositing single or mixed oxide layers or films by
MOCVD using a rare earth metal precursors having a ligand of the
general formula OCR'(R.sup.2)CH.sub.2X, wherein R.sup.1 is H or an
alkyl group, R.sup.2 is an optionally substituted alkyl group and X
is selected from OR and NR.sub.2, wherein R is an alkyl group or a
substituted alkyl group, in which the precursor is contained in a
metalorganic bubbler.
18. A method of depositing single or mixed oxide layers or films by
MOCVD using a rare earth metal precursors having a ligand of the
general formula OCR.sup.1(R.sup.2)CH.sub.2X, wherein R.sup.1 is H
or an alkyl group, R.sup.2 is an optionally substituted alkyl group
and X is selected from OR and NR.sub.2, wherein R is an alkyl group
or a substituted alkyl group, or by liquid injection MOCVD, in
which the precursor is dissolved in an appropriate inert organic
solvent and then evaporated into the vapour phase using a heated
evaporator.
19. A method as claimed in claim 18, wherein the solvent is
selected from aliphatic hydrocarbons, aromatic hydrocarbons and
aliphatic and cyclic ethers.
20. A method as claimed in claim 19, wherein the aliphatic
hydrocarbon solvent is selected from hexane, heptane and
nonane.
21. A method as claimed in claim 19, wherein the aromatic
hydrocarbon solvent is toluene.
22. A method as claimed in any one of claims 18 to 21, wherein the
solvent contains an additive selected from polydentate ethers and
donor functionalised alcohols.
23. A method as claimed in claim 22, wherein the polydentate ether
is selected from diglyme,
CH.sub.3--O--(CH.sub.2CH.sub.2O).sub.2CH.sub.3, triglyme,
CH.sub.3--O--(CH.sub.2CH.sub.2O).sub.3CH.sub.3, and tetraglyme,
CH.sub.3--O--(CH.sub.2CH.sub.2O).sub.4CH.sub.3.
24. A method as claimed in claim 22, wherein the donor
functionalised alcohol is 1-methoxy-2-methyl-2-propanol
HOCMe.sub.2CH.sub.2OMe (mmpH).
25. A method as claimed in claim 22, 23 or 24, wherein the amount
of additive added to the solvent is at least 3 mol. equiv.:mol.
equiv of precursor.
26. A method as claimed in claim 25, wherein the amount of additive
added to the solvent is in the region of 3 mol. equiv.
27. A method as claimed in any one of claims 18 to 26, wherein the
precursor has the following general formula:
M[OCR.sup.1(R.sup.2)(CH.sub.2).sub.nX].sub.3 wherein M is a rare
earth metal R.sup.1 is H or an alkyl group, R.sup.2 is an
optionally substituted alkyl group and X is selected from OR and
NR.sub.2, wherein R is an alkyl group or a substituted alkyl group,
n=1 to 4.
28. A method as claimed in any one of claims 18 to 27, wherein M is
praseodymium.
29. A method as claimed in any one of claims 18 to 28, wherein the
ligand of the formula OCR.sup.1 (R.sup.2)(CH.sub.2).sub.nX is
1-methoxy-2-methyl-2-propanolate (mmp) [OCMe.sub.2CH.sub.2OMe].
30. A method as claimed in any one of claims 18 to 28, wherein the
ligand is chosen from the group of OCH(Me)CH.sub.2OMe,
OCEt.sub.2CH.sub.2OMe, OCH(Et)CH.sub.2OMe,
OC(Pr.sup.i).sub.2CH.sub.2OMe, OCH(Pr.sup.i)CH.sub.2OMe,
OC(Bu.sup.t).sub.2CH.sub.2OMe, OCH(Bu.sup.t)CH.sub.2OMe,
OCH(Bu.sup.t)CH.sub.2OEt, OC(Bu.sup.t).sub.2CH.sub.2OEt,
OC(Pr.sup.i).sub.2CH.sub.2OEt, OCH(Bu.sup.t)CH.sub.2NEt.sub.2,
OC(Pr.sup.i).sub.2CH.sub.2OC.sub.2H.sub.4OMe and
OC(Bu.sup.t)(CH.sub.2OPr.sup.i).sub.2.
31. A method as claimed in any one of claims 18 to 30, wherein the
precursor is Pr(mmp).sub.3.
32. A method as claimed in any one of claims 18 to 30, wherein the
precursor is La(mmp).sub.3.
33. A method as claimed in any one of claims 18 to 30, wherein the
precursor is Gd(mmp).sub.3.
34. A method as claimed in any one of claims 18 to 30, wherein the
precursor is Nd(mmp).sub.3.
35. A method of depositing single or mixed oxide layers or films by
atomic layer deposition (ALD) using a rare earth metal precursors
having a ligand of the general formula OCR.sup.1(R.sup.2)CH.sub.2X,
wherein R.sup.1 is H or an alkyl group, R.sup.2 is an optionally
substituted alkyl group and X is selected from OR and NR.sub.2,
wherein R is an alkyl group or a substituted alkyl group.
36. A method as claimed in claim 35, wherein metal oxide film being
deposited is a praseodymium oxide film.
37. A method of depositing single or mixed oxide layers or films by
a non-vapour phase deposition technique using a rare earth metal
precursors having a ligand of the general formula
OCR.sup.1(R.sup.2)CH.sub.2X, wherein R.sup.2 is H or an alkyl
group, R.sup.2 is an optionally substituted alkyl group and X is
selected from OR and NR.sub.2, wherein R is an alkyl group or a
substituted alkyl group.
38. A method as claimed in claim 37, wherein the technique used is
selected from sol-gel deposition and metal-organic
decomposition.
39. A method as claimed in any one of claims 17 to 38, wherein M is
selected from La, Ce, Gd, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, Tin, Yb
and Lu as well as Group IIIB elements including Sc and Y.
40. A method as claimed in any one of claims 17 to 39 carried out
with appropriate co-precursors, for the MOCVD of multi-component
oxides.
Description
[0001] This invention concerns precursors for deposition of metal
oxide layers or films, methods of making such precursors and
methods of depositing metal oxide layers or films using such
precursors. This invention is particularly, but not exclusively,
concerned with precursors for the growth of praseodymium oxide and
other lanthanide (rare earth) metal oxides by chemical vapour
deposition.
[0002] Rare-earth oxides M.sub.2O.sub.3 (M=Pr, La, Gd, Nd) are good
insulators due to their large band-gaps (eg. 3.9 eV for
Pr.sub.2O.sub.3, 5.6 eV for Gd.sub.2O.sub.3), they have high
dielectric constants (Gd.sub.2O.sub.3 .kappa.=16, La.sub.2O.sub.3
.kappa.=27, Pr.sub.2O.sub.3 .kappa.=26-30) and higher thermodynamic
stability on silicon than ZrO.sub.2 and HfO.sub.2, making them very
attractive materials for high-.kappa. dielectric applications.
Another attractive feature of some rare earth oxides (eg.
Pr.sub.2O.sub.3, Gd.sub.2O.sub.3) is their relatively close lattice
match to silicon, offering the possibility of epitaxial growth,
eliminating problems related to grain boundaries in polycrystalline
films.
[0003] Metalorganic chemical vapour deposition (MOCVD) is an
attractive technique for the deposition of these materials,
offering the potential for large area growth, good composition
control and film uniformity, and excellent conformal step coverage
at device dimensions less than 2 .mu.m, which is particularly
important in microelectronics applications.
[0004] An essential requirement for a successful MOCVD process is
the availability of precursors with the appropriate physical
properties for vapour phase transport and a suitable reactivity for
deposition. There must be an adequate temperature window between
evaporation and decomposition, and for most electronics
applications oxide deposition is restricted to temperatures in the
region of 500.degree. C., to prevent degradation of the underlying
silicon circuitry and metal interconnects.
[0005] Pr.sub.2O.sub.3 thin films have previously been deposited by
physical vapour deposition techniques such as MBE and pulsed laser
deposition. Metalorganic chemical vapour deposition (MOCVD) has a
number of potential advantages over these techniques, such as large
area growth capability, good composition control, high film
densities and excellent conformal step coverage, but there have
been very few reports on the MOCVD of Praseodymium oxide, due
largely to a lack of suitable precursors.
[0006] Recently the MOCVD of a range of praseodymium-oxides
(PrO.sub.2, Pr.sub.6O.sub.11, Pr.sub.2O.sub.3) has been reported
using Pr(thd).sub.3 (thd=2,2,6,6,-tetramethylheptane-3,5-dionate)
(R. Lo Nigro, R. G. Toro, G. Malandrino, V. Raineri, I. L. Fragala,
Proceedings of EURO CVD 14, Apr. 27-May 2, 2003, Paris France (eds.
M. D. Allendorf, F. Maury, F. Teyssandier), Electrochem. Soc. Proc.
2003, 2003-08, 915). However, the deposition temperature used
(750.degree. C.) is incompatible with the low deposition
temperature generally required for microelectronics applications,
where high growth temperatures can lead to problems such as
increased dopant diffusion. The use of [Pr(thd).sub.3] may also
lead to the presence in the Pr-oxide film of residual carbon, a
common contaminant in oxide films grown using metal
.beta.-diketonates [Pr(hfa).sub.3(diglyme)] Pr(hfa).sub.3 diglyme
(hfa=1,1,1,5,5,5-hexafluoro-2,4-pentanedionate, diglyme
.dbd.CH.sub.3--O--(CH.sub.2CH.sub.2O).sub.2CH.sub.3) was also
investigated by these researchers, but led only to the unwanted
oxyfluoride phase, PrOF.
[0007] Metal alkoxides have been widely used in the MOCVD of metal
oxides, and generally allow lower growth temperatures than the more
thermally stable metal .beta.-diketonate precursors. There are no
reports in the literature into the use of rare-earth alkoxide
precursors in MOCVD. This is because the large ionic radius of the
highly positively charged lanthanide(III) ions leads to the
formation of bridging intermolecular metal-oxygen bonds, resulting
in the majority of the simple alkoxide complexes being polymeric or
oligomeric, with a corresponding low volatility which makes them
unsuitable for MOCVD applications.
[0008] An object of this invention is to provide stable volatile
rare earth metal oxide precursors suitable for use in chemical
vapour deposition techniques.
[0009] It has been surprisingly found that the donor functionalised
alkoxy ligand 1-methoxy-2-methyl-2-propanolate
[OCMe.sub.2CH.sub.2OMe, mmp] is effective in inhibiting
oligomerisation in praseodymium alkoxide complexes, as well as
increasing the ambient stability of the complexes.
[0010] Accordingly the present invention provides rare earth metal
precursors for use in MOCVD techniques having a ligand of the
general formula OCR.sup.1(R.sup.2)CH.sub.2X, wherein R.sup.1 is H
or an alkyl group, R.sup.2 is an optionally substituted alkyl group
and X is selected from OR and NR.sub.2, wherein R is an alkyl group
or a substituted alkyl group.
[0011] Preferred precursors according to the invention have the
following general formula:
M[OCR.sup.1(R.sup.2)(CH.sub.2).sub.nX].sub.3
[0012] wherein M is a rare earth metal, especially praseodymium,
R.sup.1 is H or an alkyl group, R.sup.2 is an optionally
substituted alkyl group and X is selected from OR and NR.sub.2,
wherein R is an alkyl group or a substituted alkyl group, n=1 to
4.
[0013] The preferred ligand of the formula
OCR.sup.1(R.sup.2)(CH.sub.2).sub.nX (n=1) is
1-methoxy-2-methyl-2-propanolate (mmp) [OCMe.sub.2CH.sub.2OMe], but
other donor functionalised alkoxide ligands may be used. These may
include but are not limited to OCH(Me)CH.sub.2OMe,
OCEt.sub.2CH.sub.2OMe, OCH(Et)CH.sub.2OMe,
OC(Pr.sup.i).sub.2CH.sub.2OMe, OCH(Pr.sup.i)CH.sub.2OMe,
OC(Bu.sup.t).sub.2CH.sub.2OMe, OCH(Bu.sup.t)CH.sub.2OMe,
OCH(Bu.sup.t)CH.sub.2OEt, OC(Bu.sup.t).sub.2CH.sub.2OEt,
OC(Pr.sup.i).sub.2CH.sub.2OEt, OCH(Bu.sup.t)CH.sub.2NEt.sub.2,
OC(Pr.sup.i).sub.2CH.sub.2OC.sub.2H.sub.4OMe and
OC(Bu.sup.t)(CH.sub.2OPr.sup.i).sub.2.
[0014] The invention further provides a first method of making rare
earth metal oxide precursors for use in MOCVD techniques comprising
reacting HOCR.sup.1(R.sup.2)(CH.sub.2).sub.nX, wherein R.sup.1,
R.sup.2 and X are as defined above, such as mmpH, with the
corresponding rare earth metal alkylamide M(NR.sub.2).sub.3 or
silylamide precursor M(N(SiR.sub.3).sub.2).sub.3, especially
praseodymium silylamide precursor, Pr{N(SiMe.sub.3).sub.2}.sub.3,
in appropriate molar proportions, wherein R=alkyl, such as, for
example, Me, Et and Pr.sup.i.
[0015] According to the invention an alternative method of general
synthesis of lanthanide and rare earth element complexes of the
formula M[OCR.sup.1(R.sup.2)CH.sub.2X].sub.3 as defined above, such
as, Ln(mmp).sub.3, involves the salt exchange reaction of
Ln(NO.sub.3).sub.3(tetraglyme) with appropriate molar equivalents
of Na(M[OCR.sup.1(R.sup.2)CH.sub.2X].sub.3, such as Na(mmp), in
tetrahydrofuran solvent. A similar method may be used for the
preparation of Sc(mmp).sub.3 and Y(mmp).sub.3.
[0016] Precursors according to the invention may be used in
depositing single or mixed oxide layers or films by conventional
MOCVD, in which the precursor is contained in a metalorganic
bubbler, or by liquid injection MOCVD, in which the precursor is
dissolved in an appropriate inert organic solvent and then
evaporated into the vapour phase using a heated evaporator.
Appropriate solvents include aliphatic hydrocarbons, such as
hexane, heptane and nonane, aromatic hydrocarbons such as toluene,
and aliphatic and cyclic ethers. Additives such as polydentate
ethers including diglyme,
CH.sub.3--O--(CH.sub.2CH.sub.2O).sub.2CH.sub.3, triglyme,
CH.sub.3--O--(CH.sub.2CH.sub.2O).sub.3CH.sub.3, tetraglyme,
CH.sub.3--O--(CH.sub.2CH.sub.2O).sub.4CH.sub.3, and donor
functionalised alcohols such as 1-methoxy-2-methyl-2-propanol
HOCMe.sub.2CH.sub.2OMe (mmpH) may also be added to the solvent, as
these may render the precursors of the invention, especially
Ln(mmp).sub.3 (Ln=lanthanide such as La, Pr, Gd, Nd etc.), less
reactive to air and moisture and may improve the evaporation
characteristics of the precursor solution. The amount of additive
added to the solvent will typically be in the region of 3 mol.
equiv.: 1 mol. equiv. precursor. Lower amounts of additive are less
effective but amounts of more than 3 mol. equiv. may be used.
[0017] The precursors may also be suitable for use in the
deposition of praseodymium oxide films by other chemical vapour
deposition techniques, such as atomic layer deposition (ALD).
[0018] The M[OCR.sup.1(R.sup.2)(CH.sub.2).sub.nX].sub.3 precursor
may also be suitable for the deposition of rare-earth oxide films
using non-vapour phase deposition techniques, such as sol-gel
deposition and metal-organic decomposition, where the new complexes
may undergo a more controlled hydrolysis reactions than simple
M(OR).sub.3 complexes.
[0019] Other volatile rare earth precursors for use in MOCVD, ALD
or sol-gel processes according to the invention may include
lanthanide (rare-earth) elements, such as La, Ce, Gd, Nd, Pm, Sm,
Eu, Tb, Dy, Ho, Er, Tm, Yb and Lu as well as Group IIIB elements
including Sc and Y.
[0020] The precursors according to the invention can also be used,
in combination with an appropriate silicon precursor for the MOCVD
of lanthanide silicates, LnSi.sub.xO.sub.y, and with appropriate
co-precursors for the MOCVD of multi-component oxides, such as
Pr.sub.xM.sub.yO.sub.z containing praseodymium, or other rare earth
metals with metals (M) from other groups of the periodic table.
[0021] The invention will now be further described by means of the
following Examples and with reference to the accompanying drawings,
in which:
[0022] FIG. 1 shows the X-ray crystal structure of
[LiPr(mmp).sub.3Cl].sub.2;
[0023] FIG. 2 shows XRD spectra of Pr-oxide films deposited at
400.degree. C. and 600.degree. C. from [Pr(mmp).sub.3]. * denotes
the dominant (101) reflection of the secondary
.theta.-Pr.sub.2O.sub.3 phase;
[0024] FIG. 3 is an SEM image of a Pr-Oxide film deposited at
400.degree. C. from [Pr(mmp).sub.3];
[0025] FIG. 4 is an X-ray diffraction pattern of a film of
lanthanum oxide deposited at 450.degree. C. from La(mmp).sub.3;
[0026] FIG. 5 is a scanning electron micrograph (SEM) of a fracture
sample of the lanthanum oxide film of Example 4;
[0027] FIG. 6 is a .sup.1H NMR spectrum of a solution of
La(mmp).sub.3 in toluene;
[0028] FIG. 7 is a .sup.1 NMR spectrum of a solution of
Pr(mmp).sub.3 in toluene;
[0029] FIG. 8 is a .sup.1H NMR spectrum of a solution of
La(mmp).sub.3 in toluene with 3 mol. equiv. of added
tetraglyme;
[0030] FIG. 9 is a .sup.1H NMR spectrum of a solution of
Pr(mmp).sub.3 in toluene with 3 mol. equiv. of added
tetraglyme;
[0031] FIG. 10 shows .sup.1H NMR data of a solution of
La(mmp).sub.3 in toluene with 3 mol. equiv. of added mmpH; and
[0032] FIG. 11 shows .sup.1H NMR data of a solution of
Pr(mmp).sub.3 in toluene with 3 mol. equiv. of added mmpH.
EXAMPLE 1
Preparation of Pr(mmp).sub.3
[0033] MmpH (0.487 cm.sup.3, 4.23 mmol) was added to a solution of
[Pr{N(SiMe.sub.3).sub.2}.sub.3] (0.878 g, 1.41 mmol) in toluene (80
cm.sup.3). The solution was stirred at room temperature for 10 min
and then solvent and HN(SiMe.sub.3).sub.2 was removed in vacuo to
give a green oil.
[0034] Microanalysis: Found. C, 38.0; H, 6.60%. Calculated. For
C.sub.15H.sub.33O.sub.6Pr C, 40.01; H, 7.39%.
[0035] IR (.nu. cm.sup.-1, neat liquid, NaCl plates): 2960 vs; 1496
in; 1458 s; 1383 m; 1357 s; 1274 s, 1229 vs, 1205 s; 1171 vs; 1113
vs; 1086 vs; 997 vs; 967 vs; 943 vs; 915 m; 828 w; 786 m; 730 s;
695 m.
[0036] NMR spectroscopy (CDCl.sub.3; 400 MHz): (All resonances are
broadened due to the paramagnetic Pr.sup.3+ (4f.sup.2). Integrals
of these broad resonances are not reported due to the lack of
precision): 100.5, 72.5, 69.7, 67.0, 64.0, 63.7, 62.4, 60.7, 58.4,
57.0, 56.0, 54.0, 53.5, 50.5, 48.2, 47.2, 42.2, 40.7, 19.1, 18.6,
18.0, 17.7, 15.3, 13.9, 12.7, 11.2, 3.1, 1.2, -4.7, -10.5, -11.8,
-12.5, -13.0, -15.5, -19.0, -20.5, -24.4, -30.2, -40.1, -43.6,
-45.3, -46.2, -54.0
[0037] The liquid nature of Pr(mmp).sub.3 precludes structural
characterisation by single crystal X-ray diffraction, but In the
presence of LiCl a crystalline complex with the formula
[LiPr(mmp).sub.3Cl].sub.2 was isolated, providing further good
evidence that the stoichiometry of the oil was [Pr(mmp).sub.3].
This complex was characterized by single crystal X-ray diffraction
and its structure is shown in FIG. 1 of the drawings.
EXAMPLE 2
[0038] Pr(mmp).sub.3 was found to be a suitable precursor for the
deposition of praseodymium oxide thin films by MOCVD. The
praseodymium oxide films were deposited by liquid injection MOCVD
using a 0.1M solution of Pr(mmp).sub.3 in toluene (14 cm.sup.3) to
give a 0.1 M solution. The addition of tetraglyme
CH.sub.3--O--(CH.sub.2CH.sub.2O).sub.4CH.sub.3 was found to
stabilise the Pr(mmp).sub.3 solution by making it less reactive to
air and moisture and improving the transport properties of the
precursor. The growth conditions used to deposit Pr-oxide thin
films by liquid injection MOCVD using a toluene solution of
Pr(mmp).sub.3 are summarised in Table 1.
TABLE-US-00001 TABLE 1 Reactor pressure 1 mbar Evaporator
temperature 170.degree. C. Substrate temperature 350-600.degree. C.
Precursor solution concentration 0.1M in toluene with 3 mol equiv.
of added tetraglyme Precursor solution injection rate 8 cm.sup.3
hr.sup.-1 Argon flow rate 400 cm.sup.3 min.sup.-1 Oxygen flow rate
100 cm.sup.3 min.sup.-1 Substrates Si(100) Typical oxide growth
rates 0.2 .mu.m hr.sup.-1
The identity of the films was confirmed as praseodymium oxide by as
X-ray diffraction analysis (see FIG. 2 of the drawings), which
indicated that the films comprise a major .beta.-Pr.sub.6O.sub.11
phase with a minor component of the hexagonal
.theta.-Pr.sub.2O.sub.3 phase. Reports elsewhere (R. Lo Nigro, R.
G. Toro, G. Malandrino, V. Raineri, I. L. Fragala, Proceedings of
EURO CVD 14, Apr. 27-May 2, 2003, Paris France (eds. M. D.
Allendorf, F. Maury, F. Teyssandier), Electrochem. Soc. Proc. 2003,
2003-08, 915) indicate that the proportions of the
.beta.-Pr.sub.6O.sub.11 phase and the .theta.-Pr.sub.2O.sub.3 can
be controlled via the partial pressure of oxygen used during MOCVD
growth.
[0039] Analysis of the films by scanning electron microscropy (SEM)
showed that all the as-grown films exhibited smooth surfaces and
uniform cross sectional thicknesses. The cross section of a film
grown at 400.degree. C. is shown in FIG. 3 of the drawings and
shows no evidence of features such as columnar growth, which has
been observed in other high-k dielectric films such as HfO.sub.2
and ZrO.sub.2.
[0040] Point energy dispersive X-ray analyses of the films
indicates only Pr from the thin film and silicon from the
underlying substrate material.
[0041] Further analysis by auger electron spectroscopy (AES)
analysis of Pr-oxide films deposited from [Pr(mmp).sub.3] (see
Table 2) showed that the films are pure Pr-oxide, with no
detectable carbon.
TABLE-US-00002 TABLE 2 Deposition temperature Composition (at. %)
Pr/O Sample (.degree. C.) Pr O C ratio 1 350 30.3 69.7 ND 2.3 4 600
32.9 67.1 ND 2.0
EXAMPLE 3
Preparation of La(mmp).sub.3
[0042] MmpH (3 mol. equiv.) was added to a solution of
[La{N(SiMe.sub.3).sub.2}.sub.3] (1 mol equiv.) in toluene. The
solution was stirred at room temperature for 10 min and then
solvent and HN(SiMe.sub.3).sub.2 was removed in vacuo to give the
product.
[0043] Microanalysis: Found. C, 40.0; H, 7.4%. Calcd. For
C.sub.15H.sub.33O.sub.6La C, 40.2, H, 7.4%.
[0044] IR (.nu. cm.sup.-1, neat liquid, NaCl): 2960 vs; 1496 m;
1457 s; 1384 in; 1357 s; 1261 s; 1229 vs; 1172 vs; 1090 vs; 1084
vs; 1001 s; 965 vs; 944 s; 914 m; 841 m; 821 m; 794 s; 730 s; 695
m.
[0045] NMR spectroscopy C.sub.6D.sub.6 (400 MHz) Main resonances:
.delta. (ppm): 3.16 br singlet; 3.08 br singlet (total 5H); 2.65
singlet; 1.27 singlet (6H). Other resonances 3.2-4 ppm, complex
pattern (total approx 2H); 1.2-1.8 ppm, complex pattern (total
approx 4H).
[0046] The same general preparative method can be used for the
synthesis of other M(mmp).sub.3 complexes where M=Group IIIB
element such as Sc and Y, or a lanthanide (rare earth) element such
as, Ce, Gd or Nd.
EXAMPLE 4
[0047] La(mmp).sub.3 was found to be a suitable precursor for the
deposition of lanthanum oxide thin films by MOCVD. Growth
conditions used to deposit La-oxide thin films by liquid injection
MOCVD using a toluene solution of La(mmp).sub.3 are summarised in
Table 3.
TABLE-US-00003 TABLE 3 Substrate Temperature 300-600.degree. C.
Evaporator Temperature 170.degree. C. Pressure 1 mbar Injection
Rate 8 cm.sup.3h.sup.-1 Solvent Toluene + 3 mol. eq. tetraglyme
Concentration 0.1M Argon flow rate 400 cm.sup.3min.sup.-1 Oxygen
flow rate 100 cm.sup.3min.sup.-1 Run time 1 h
[0048] The X-ray diffraction pattern (see FIG. 4 of the drawings)
of a film deposited at 450.degree. C. exhibits three dominant
diffraction peaks attributed to the (100), (002) and (101)
reflections measured at 2.theta. values of 25.1.degree.,
27.9.degree. and 29.7.degree. respectively. The approximate ratio
of intensities of these peaks is consistent with the random powder
diffraction pattern of La.sub.2O.sub.3 with a hexagonal structure.
The width of the observed reflections is notable and consistent
with either very small grain size or the transformation of the
oxide to the monoclinic LaO(OH) arising from exposure of the film
to the ambient environment.
[0049] The atomic composition of the LaO.sub.x films was determined
using Auger electron spectroscopy (AES), and the results are
summarized in Table 4.
TABLE-US-00004 TABLE 4 AES analysis of La-oxide films grown by
MOCVD Argon flow Deposition rate Oxygen Com- Film temperature
(cm.sup.3 flow rate position (atom %) no. (.degree. C.) min.sup.-1)
(cm.sup.3 min.sup.-1) La O O/La 317 300 400 100 29.0 71.0 2.4 314
350 400 100 35.0 65.0 1.8 318 400 400 100 33.8 66.2 1.9 309 450 400
100 31.3 68.7 2.2 316 500 400 100 33.0 67.0 2.0 313 550 400 100
33.7 66.3 2.0 315 600 400 100 31.8 68.2 2.1 319 450 500 0 34.4 65.6
1.9 320 450 250 250 32.3 67.7 2.1
[0050] The O:La ratios of 1.8-2.4 are consistent with the films
being La.sub.2O.sub.3 containing excess oxygen (expected O:La ratio
in La.sub.2O.sub.3=1.5). Carbon was not detected in any of the
films at the estimated detection limit of <0.5 at.-% and
carbon-free La-oxide films were obtained, even in the absence of
oxygen, so that [La(mmp).sub.3] is effectively acting as a
"single-source" oxide precursor.
[0051] A scanning electron micrograph (SEM) of a fracture sample
from that lanthanum oxide film deposited at 450.degree. C. is shown
in FIG. 5 of the drawings. A columnar growth habit is discernable
which has associated `hillock` features on the free growth surface
causing a fine surface roughening effect.
EXAMPLE 5
Preparation of Nd(mmp).sub.3
[0052] MmpH (3 mol. equiv.) was added to a solution of
[Nd{N(SiMe.sub.3).sub.2}.sub.3] (1 mol. equiv.) in toluene. The
solution was stirred at room temperature for 10 min. and then
solvent and HN(SiMe.sub.3).sub.2 was removed in vacuo to give the
product.
[0053] Microanalysis: Found: C, 38.8; H, 6.9%. Calcd. For
C.sub.15H.sub.33O.sub.6Nd, C, 39.7; H, 7.33%.
[0054] Infrared data: recorded as thin film between NaCl plates
(cm.sup.-1) 2963 vs; 1496 m; 1457 s; 1384 m; 1357 s; 1275 s; 1231
vs; 1173 vs; 1117 vs; 1086 vs; 1010 s; 968 vs; 915 m; 823 m; 793 a;
730 s; 695 m
[0055] .sup.1H NMR (CDCl.sub.3) [resonances are broadened due to
paramagnetism of Nd.sup.3+ (4f.sup.3)]: 35.1, 31.7, 30.9, 18.8,
17.4, 15.8, 12.6, 11.5, 8.2, 5.6, 1.2, -9.0, -9.6, -18.2, -24.5,
-25.6, -26.0, -55.8, -57.5
EXAMPLE 6
Use of Additives to Stabilise Precursor Solutions
[0056] The .sup.1H NMR spectra of [La(mmp).sub.3] and
[Pr(mmp).sub.3] in toluene solution are shown in FIGS. 6 and 7,
respectively. The complexity of the .sup.1H NMR. data indicates
that the structure of both these compounds are extremely complex,
and particularly in the case of La, the complexity of the spectrum
increases with time. This indicates that there is a significant
amount of irreversible molecular aggregation in solution. This
process is probably due to condensation reactions to form
oxo-bridged oligomers; such reactions are well documented in
lanthanide alkoxide chemistry. The resonances are also broadened,
possibly due to inter-molecular ligand exchange reactions, commonly
observed in solutions of metal alkoxide complexes.
[0057] Significantly, the addition of 3 mol. equivalents of the
polydentate oxygen donor ligand tetraglyme,
(CH.sub.3--O--(CH.sub.2CH.sub.2O).sub.4CH.sub.3), to the precursor
solutions results in much simpler .sup.1H NMR spectra (FIGS. 8 and
9). This strongly suggests that the presence of
(CH.sub.3--O--(CH.sub.2CH.sub.2O).sub.4CH.sub.3) inhibits molecular
aggregation. The observation that the tetraglyme resonances are not
subject to paramagnetic shifting in [Pr(mmp).sub.3][tetraglyme]
indicates that the tetraglyme is not bonded directly to Pr, and we,
therefore, conclude that stable adducts of the type
[Ln(mmp).sub.3(tetraglyme)] are not formed.
[0058] The addition of one mole excess of [mmpH]
(HOCMe.sub.2CH.sub.2OMe) to toluene solutions of La(mmp.sub.3) or
Pr(mmp).sub.3 also results in simpler .sup.1H NMR spectra (see
FIGS. 10 and 11 of the drawings) and has a similar stabilizing
effect. The simplicity of the .sup.1H NMR spectra indicates that
mmp and mmpH are in rapid exchange and there is no uncoordinated
mmpH. The addition of tetraglyme or mmpH to solutions of
[Ln(mmp).sub.3] was found to enhance air/moisture stability as well
as prevent aggregate formation. The mechanism of this stabilization
has not been established, but it is likely to be due to some form
of shielding of the lanthanide metal centre from oxygen atoms on
mmp ligands on neighbouring molecules.
EXAMPLE 7
Preparation of Gd(mmp).sub.3
[0059] [Gd(mmp).sub.3] was synthesised by the addition of mmpH (3
mol. equiv.) to a solution of [Gd{N(SiMe.sub.3).sub.2}.sub.3] (1
mol equiv.) in toluene. The solution was stirred at room
temperature for 10 min and then the solvent and liberated
HN(SiMe.sub.3).sub.2 were removed in vacuo to give the product as a
green oil. The product was confirmed by elemental microanalysis for
C and H.
EXAMPLE 8
Growth of Gadolinium Oxide Using Gd(mmp).sub.3
[0060] Gadolinium oxide films were deposited on Si(100) substrates
at 1 mbar using a liquid injection MOCVD reactor. The films were
deposited over the temperature range 300-600.degree. C. using a
0.1M solution of [Gd(mmp).sub.3] in toluene, with 3 equivalents of
added tetraglyme using the same growth conditions to those given in
Table 3. Gadolinium oxide films were also grown on GaAs(100) using
a 0.1M solution of [Gd(mmp).sub.3] in toluene, with 3 equivalents
of added tetraglyme, in the absence of added oxygen.
[0061] The films grown on Si(100) and GaAs(100) substrates were
confirmed to be Gadolinium oxide by Auger electron spectroscopy
(AES) as shown in the following Table 5:--
TABLE-US-00005 TABLE 5 Atomic composition (at.-%) of gadolinium
oxide films measured by AES* Depo- Argon Oxygen sition flow flow
rate Film temp. rate (cm.sup.3 (cm.sup.3 no. Substrate (.degree.
C.) min.sup.-1) min.sup.-1) Gd O O/Gd 1 Si(100) 450 500 0 37.6 62.4
1.7 2 GaAs(100) 450 500 0 36.9 63.1 1.7 *H not analysed for.
[0062] X-ray diffraction data for Gd.sub.2O.sub.3 films showed that
at growth temperatures above 450 C , the GdO.sub.x films
crystallize as Gd.sub.2O.sub.3 with a C-type structure exhibiting a
preferred (111) orientation. At lower growth temperatures the data
exhibited no diffraction features suggesting an amorphous
disordered structure.
[0063] The diffraction pattern of the Gd.sub.2O.sub.3 film
deposited on GaAs(100) at 450 C was dominated by the (222)
reflection. This indicates a strong preferred orientation or a
heteroepitaxial relation with the underlying GaAs.
EXAMPLE 9
Stabilisation of M(mmp).sub.3 (M=Rare Earth Element) Precursor
Solutions by the Addition of Donor Additives
[0064] The .sup.1H NMR spectra of [La(mmp).sub.3] and
[Pr(mmp).sub.3] in toluene solution are shown in FIGS. 6 and 7,
respectively. The addition of 3 mole equivalents of the polydentate
oxygen donor ligand tetraglyme,
--(CH.sub.3--O--(CH.sub.2CH.sub.2O).sub.4CH.sub.3) to the precursor
solutions of M(mmp).sub.3 (M=La, Pr) results in much simpler
.sup.1H NMR spectra (FIGS. 8 and 9 of the drawings) and renders the
precursor solutions less air sensitive, and significantly improves
the evaporation characteristics of the precursor solution in liquid
injection MOCVD applications.
[0065] This strongly suggests that the presence of
(CH.sub.3--O--(CH.sub.2CH.sub.2O).sub.4CH.sub.3) inhibits molecular
aggregation. The observation that the tetraglyme resonances are not
subject to paramagnetic shifting in [Pr(mmp).sub.3][tetraglyme]
indicates that the tetraglyme is not bonded directly to Pr, and we,
therefore, conclude that stable adducts of the type
[Ln(mmp).sub.3(tetraglyme)] are not formed.
[0066] The addition of one mole excess of
1-methoxy-2-methyl-2-propanol, [HOCMe.sub.2CH.sub.2OMe] (mmpH) to
solutions of M(mmp).sub.3 (M=rare earth element) in toluene has a
similar stabilizing effect (see FIGS. 10 and 11). In the case of
[Ln(mmp).sub.3(mmpH)] the simplicity of the .sup.1H NMR spectrum
indicates that mmp and mmpH are in rapid exchange and there is no
uncoordinated mmpH. The addition of tetraglyme or mmpH to solutions
of [Ln(mmp).sub.3] was found to enhance air/moisture stability as
well as prevent aggregate formation.
[0067] The mechanism of this stabilization has not been
established, but it is likely to be due to some form of shielding
of the Ln metal centre from oxygen atoms on mmp ligands on
neighbouring molecules.
EXAMPLE 10
Growth of Neodymium Oxide Using Nd(mmp).sub.3
[0068] Neodymium oxide films were deposited on Si(100) substrates
at 1 mbar using a liquid injection MOCVD reactor. The films were
deposited over the temperature range 250-600.degree. C. using a 0.1
M solution of [Nd(mmp).sub.3] in toluene, with 3 equivalents of
added tetraglyme employing the equivalent growth conditions to
those given in Table 3. Neodymium oxide films were also grown on
GaAs(100) using a 0.1M solution of [Gd(mmp).sub.3] in toluene, with
3 equivalents of added tetraglyme, in the absence of added
oxygen.
[0069] The films grown on Si(100) and GaAs(100) substrates were
confirmed to be neodymium oxide, Nd.sub.2O.sub.3, by Auger electron
spectroscopy (AES) as shown in the following Table 6:--
TABLE-US-00006 TABLE 6 Atomic composition (at.-%) of the NdO.sub.x
films measured by AES* Argon Oxygen flow flow Deposition rate rate
Film temperature (cm.sup.3) (cm.sup.3 no. Substrate (.degree. C.)
min.sup.-1) min.sup.-1) Nd O O/Nd 1 Si(100) 300 400 100 37 63 1.7 2
Si(100) 450 400 100 40.1 59.9 1.5 3 Si(100) 500 400 100 38.7 61.3
1.6 4 Si(100) 450 500 0 41.2 58.8 1.4 5 Si(100) 450 450 50 41.8
58.2 1.4 6 Si(100) 450 350 150 41.7 58.3 1.4 7 Si(100) 450 300 200
45.5 54.5 1.2 8 Si(100) 450 250 250 42.1 57.9 1.4 9 GaAs(100) 450
500 0 40.6 59.4 1.5 *H not analysed for
* * * * *