Precursors and processes for making metal oxides

A first metal, an alcohol, and a carboxylic acid are reacted to form a metal alkoxycarboxylate which is then reacted with an alkoxide and/or a carboxylate of a second metal to form a precursor. Alternatively, a metal carboxylate and a metal alkoxide are combined and heated to form a precursor. In either alternative, the precursor includes all or most of the metal-oxygen-metal bonds of a desired metal oxide and a carboxylate ligand. The precursor is applied to a substrate, dried and annealed to form the metal oxide, such as BST. The metal-oxygen-metal bonds in the precursor permit the desired metal oxide to be formed from the precursor in one step, providing excellent thin films suitable for integrated circuits. The carboxylate ligand provides stability to the precursor allowing it to be stored for periods common in large scale manufacturing.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention in general relates to the fabrication of metal oxides 
utilizing a precursor liquid applied to a substrate, and more particularly 
to a fabrication process in which the metal-oxygen-metal bonds of the 
final desired material are largely formed in the precursor liquid prior to 
the application of the liquid to the substrate. 
2. Statement of the Problem 
Metal oxides are well known to be useful as ferroelectrics, high dielectric 
constant materials, and to have many other applications. Recently, there 
has been much research directed toward using metal oxides in thin film 
applications, such as integrated circuits. However, their commercial use 
in such applications has been relatively limited up to the present time. 
To a significant extent, this is due to the difficulty of forming high 
quality thin films with precisely controlled composition. 
Metal oxide films have perhaps most frequently been formed by sputtering. 
See for example, Kuniaki Koyama, et al., "A Stacked Capacitor With 
(Ba.sub.x Sr.sub.1-x)TiO.sub.3 For 256M DRAM" in IDEM (International 
Electron Devices Meeting) Technical Digest, December 1991, pp. 
32.1.1-32.1.4, and U.S. Pat. No. 5,122,923 issued to Shogo Matsubara et 
al. Other fabrication methods include pulsed laser deposition, and rapid 
quenching as listed in Joshi, P. C. et al., "Structural and Optical 
Properties of Ferroelectric Thin Films By Sol-gel Technique," Appl. Phys. 
Lett., Vol 59, No. 10, November 1991. All of the above methods are 
relatively violent processes and thus inherently result in relatively poor 
control of the composition of the final thin film as a whole and variable 
composition throughout the film. To better control the composition, 
methods in which a organic liquid precursor is applied to the film and 
then decomposed to form the metal oxide have been developed. One such 
method comprises the application of a sol-gel to a substrate followed by 
heating which decomposes the sol-gel and drives off the organics to form 
the metal oxide. See for example, U.S. Pat. No. 5,028,455 issued to 
William D. Miller et al., the Joshi article cited above, and B. M. 
Melnick, et al., "Process Optimization and Characterization of Device 
Worthy Sol-Gel Based PZT for Ferroelectric Memories", in Ferroelectrics, 
Vol 109, pp. 1-23 (1990). In another method, what has been termed a "MOD" 
solution is applied to a substrate followed by heating which decomposes 
the MOD solution and drives off the organics to form the metal oxide. See 
"Synthesis of Metallo-organic Compounds for MOD Powers and Films", G. M. 
Vest and S. Singaram, Materials Research Society Symposium Proceedings, 
Vol. 60, 1986 pp. 35-42 and "Metalorganic Deposition (MOD): A Nonvacuum, 
Spin-on, Liquid-Based, Thin Film Method", J. V. Mantese, A. L. Micheli, A. 
H. Hamdi, and R. W. Vest, in MRS Bulletin, October 1989, pp. 48-53. In 
each of these prior art processes, the word "precursor" is used with two 
different meanings. Each process includes precursors for each individual 
metal, which precursors we shall call "initial precursors" herein. For 
example, in the first Vest paper referenced above, barium neodeconate is 
listed as the initial precursor of choice for the metal barium while 
bismuth 2-ethylhexanoate is listed as the initial precursor for the metal 
bismuth. The initial precursors are then dissolved in a common solvent to 
form a "final precursor" which contains all of the metals of the desired 
final thin film. Generally the sol-gel method utilizes metal alkoxides as 
the initial precursors, while the MOD technique utilizes metal 
carboxylates as the initial precursors. One sol-gel reference, the Miller 
patent referenced above, mentions one metal carboxylate, lead 
tetra-ethylhexanoate, as a possible precursor, however does not disclose 
how this may be used as a sol-gel, and furthermore rejects this precursor 
as less desirable since the large organic group was thought to result in 
more defects in the final film. The above liquid precursor methods produce 
a much better quality film than the previous more violent methods, since 
the metal and oxygen atoms are relatively uniformly distributed over the 
substrate. However, in most of the above processes, the metals in the 
precursor solution are linked by organic ligands, which ligands must be 
broken down and removed during the heating process. This creates 
relatively large distances across which the metal and oxygen atoms must 
link. This often results in cracking or other imperfections in the film, 
or requires careful control of other parameters, such as film thickness, 
drying and annealing temperatures, the substrate used etc. In other liquid 
processes, such as the sol-gel process described in Melnick, the 
metal-oxygen-metal bonds of the final metal oxide are present in some 
degree, however the precursor is highly unstable and therefore is 
difficult to use except immediately after preparation in the laboratory. 
Thus it would be highly desirable to have a fabrication process in which 
the constituents can be carefully controlled as in the sol-gel and MOD 
processes, and at the same time the metal and oxygen atoms are more 
closely associated prior to the formation of the final desired film and 
the precursors are sufficiently stable to be used in commercial 
manufacturing processes. 
3. Solution to the Problem 
The present invention solves the above problem by utilizing a mixed 
alkoxide/carboxylate initial precursor. Unlike the prior art which 
utilizes either a metal alkoxide or a metal carboxylate as the individual 
precursor for a metal, the invention utilizes a alkoxycarboxylate as the 
individual precursor for at least one metal. 
In an exemplary embodiment or the invention a first metal is reacted with 
an alcohol and a carboxylic acid to produce a metal alkoxycarboxylate 
initial precursor. Then the alkoxide of a second metal is added to the 
alkoxycarboxylate and reacted to form a final precursor containing both 
the first and second metals. In this final precursor the first and second 
metals are linked with a metal-oxygen-metal bond. A portion of the 
organics that remained in the prior art precursors until after application 
of the final precursor to the substrate are boiled out of the final 
precursor as ethers. Generally the organics which remain are alkoxide and 
carboxylate ligands which are linked to the metal oxide without 
significantly disturbing the metal-oxygen-metal bonds. The presence of the 
carboxylate ligands provide sufficient stability to the precursor against 
hydrolysis to permit it to be stored for months without significantly 
changing. During and/or after the application of the precursor to a 
substrate, these remaining organics are disassociated from the 
metal-oxygen-metal bonds, preferably by heating, thereby leaving the 
metal-oxygen-metal bonds in place. 
In another embodiment a metal carboxylate is combined with a metal alkoxide 
and heated, preferable with the addition of carboxylic acid and/or 
alcohol. Many other variations of the process are possible. 
Since a significant portion of the metal-oxygen-metal bonds of the final 
thin film are already formed in the final precursor, the resulting thin 
film is of higher quality and less susceptible to cracking and other 
defects than thin films formed with the prior art processes and 
precursors. In addition, since the metal and oxygen atoms are much more 
closely associated in the precursor, the quality of the film is less 
sensitive to the substrates and/or the process parameters used. Thus the 
precursors and process of the invention lend themselves more readily to 
large scale manufacturing. Numerous other features, objects and advantages 
of the invention will become apparent from the following description when 
read in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
1. Overview. 
Directing attention to FIG. 1, there is shown a flow chart of a generalized 
process according to the invention for forming a precursor solution for 
fabricating thin films. As indicated above, the word "precursor" is often 
used ambiguously in this art. It may mean an solution containing one metal 
or the a solution containing several metals which is applied to a 
substrate. In this discussion we shall generally refer to the individual 
precursors as "initial precursors" and the precursor as applied to the 
substrate as the "final precursor" or just "precursor" unless the meaning 
is clear from the context. In intermediate stages the solution may be 
referred to as the "intermediate precursor". In step P1 a 1st metal, 
indicated by the term metal (1), is reacted with an alcohol and a 
carboxylic acid to form a metal-alkoxocarboxylate initial precursor. A 
metal-alkoxocarboxylate is a compound of the form MX.sub.x A.sub.a, where 
M is a metal, X is a carboxylate ligand and A is an alkoxide ligand. The 
subscripts indicate the number of units of the ligand required to agree 
with the valence requirements. Metals that may be used include barium, 
strontium, tantalum, calcium, bismuth, lead, yttrium, scandium, lanthanum, 
antimony, chromium, thallium, titanium, hafnium, tungsten, niobium, 
zirconium, manganese, iron, cobalt, nickel, magnesium, zinc, and other 
elements. Alcohols that may be used include 2-methoxyethanol, 1-butanol, 
1-pentanol, 2-pentanol, 1-hexanol, 2-hexanol, 3-hexanol, 
2-ethyl-1-butanol, 2-ethoxyethanol, and 2-methyl-1-pentanol, preferably 
2-methoxyethanol. Carboxylic acids that may be used include 
2-ethylhexanoic acid, octanoic acid, and neodecanoic acid, preferably 
2-ethylhexanoic acid. In a typical second step, P2, a metal-carboxylate, a 
metal-alkoxide or both may be added to the metal-alkoxocarboxylate. Any of 
the metals listed above reacted with any of the carboxylic acids listed 
above may form the carboxylate, while any of the metals listed above 
reacted with any of the alcohols may form the alkoxide. In step P3 the 
mixture of metal-alkoxocarboxylate, metal-carboxylate and/or 
metal-alkoxide is heated and stirred as necessary to form 
metal-oxygen-metal bonds and boil off any low-boiling point organics that 
are produced by the reaction. Preferably, at least 50% of the 
metal-oxygen-metal bonds of the final desired metal oxide are formed by 
the end of this step. In step P4 the solution is diluted with an organic 
solvent to produce the final precursor of the desired concentration. A 
solvent exchange step may take place simultaneously or subsequently to 
change the solvent. Solvents that may be used include: xylenes, 
2-methoxyethanol, n-butyl acetate, n-dimethylformamide, 2-methoxyethyl 
acetate, methyl isobutyl ketone, methyl isoamyl ketone, isoamyl alcohol, 
cyclohexanone, 2-ethoxyethanol, 2-methoxyethyl ether, methyl butyl ketone, 
hexyl alcohol, 2-pentanol, ethyl butyrate, nitroethane, pyrimidine, 1, 3, 
5 trioxane, isobutyl isobutyrate, isobutyl propionate, propyl propionate, 
ethyl lactate, n-butanol, n-pentanol, 3-pentanol, toluene, ethylbenzene as 
well as many others. 
If a metal-alkoxide is added to the metal-alkoxocarboxylate and the 
solution is heated the following reactions occur: 
(1) M.sub.1 X.sub.x A.sub.a +M.sub.2 A.sub.b .fwdarw.X.sub.x M.sub.1 
--O--M.sub.2 A.sub.b-a +Et, and 
(2) M.sub.1 X.sub.x A.sub.a +M.sub.2 A.sub.b .fwdarw.A.sub.a M.sub.1 
--O--M.sub.2 A.sub.b-x +Es, 
where M.sub.1 is the first metal, M.sub.2 is the second metal, X and A and 
the subscripts are as defined above, O is oxygen, Et is an ether, and Es 
is an ester. The dashes indicate metal-oxygen-metal bonds. Generally the 
reaction of equation (1) will occur first since alkoxides react more 
readily than carboxylates. Thus ethers, which have low boiling points are 
generally formed. These ethers boil out of the precursor, thus leaving a 
reduced organic final precursor with the metal-oxygen-metal bonds of the 
final desired metal oxide already partially formed. If the heating is 
sufficient, some of the reaction (2) will also occur, creating 
metal-oxygen-metal bonds and esters. Esters generally have higher boiling 
points and remain in solution. Such high boiling point organics slow down 
the drying process after the final precursor is applied to a substrate, 
which tends to reduce cracking and defects. Thus, in either case 
metal-oxygen-metal bonds are formed and the final precursor performance is 
improved. 
If a metal-carboxylate is added to the metal-alkoxocarboxylate and the 
mixture is heated, the following reaction occurs: 
(3) M.sub.1 X.sub.x A.sub.a +M.sub.2 X.sub.y .fwdarw.A.sub.a M.sub.1 
--O--M.sub.2 X.sub.y-x +H, 
where H is a carboxylic acid anhydride. This reaction requires considerably 
more heat than the reactions (1) and (2) above, and proceeds at a much 
slower rate. 
The above reaction summary is generalized and the specific reactions that 
occur depend on the metals, alkoxides, and carboxylates used, as well as 
the amount of heat that is applied. Detailed examples will be given below. 
In FIG. 2, a flow chart showing, also in generalized form, the application 
of the final precursor according to the invention to form a thin film. In 
step P7 a substrate is provided. The substrate generally would be an 
incomplete integrated circuit, or other electrical device. Examples are 
shown in FIGS. 4 through 8. It should be understood that the FIGS. 4 
through 7 depicting capacitor devices and FIG. 8 depicting an integrated 
circuit device are not meant to be actual plan or cross-sectional views of 
any particular portion of an actual capacitor or integrated circuit 
device, but are merely idealized representations which are employed to 
more clearly and fully depict the structure and process of the invention 
than would otherwise be possible. FIG. 5 shows a cross-section of the 
wafer 1 of FIG. 2A taken through the line 5--5. FIGS. 6 and 7 depict a 
cross-section taken through a wafer similar to that of FIG. 4 but having a 
different layered structure. Referring to FIGS. 4 and 5, the wafer 1 
preferably comprises a P-type silicon substrate 2 on which an 
approximately 5000 .ANG. silicon dioxide insulating layer 4 has been wet 
grown. A thin layer 6 of titanium metal has been deposited on the silicon 
dioxide 4, preferably by sputtering in situ, and a 2000 .ANG. thick 
electrode of platinum has been deposited on the titanium 6, preferably by 
sputtering in situ. By "in situ" is meant that both the titanium and the 
platinum are sputtered without breaking vacuum. The titanium diffuses into 
the silicon dioxide and platinum and assists the platinum 8 in adhering to 
the silicon dioxide 4, and is optional. In the preferred embodiment, the 
layer 6 may also include a barrier layer of, for example, TiN. The barrier 
layer prevents ion migration between the silicon of layer 4 and the 
electrode 8 and layers 10 and 12. The structure of such adhesion layers, 
barrier layers, and electrodes are well know in the art and will not be 
discussed in detail herein. A buffer layer 10, is deposited on the 
platinum electrode 8, followed by a layer 12 of metal oxide according to 
the invention, followed by another buffer layer 14, via processes that 
will be described in detail in the examples below. Another 2000 .ANG. 
layer of platinum is deposited on the buffer layer 14. The wafer 1 is 
annealed, patterned with a photo-mask process, and etched down to the 
electrode layer 8 to produce rectangular capacitor devices 17A, 17B, etc. 
(FIG. 4 ) of various sizes separated by large areas of the electrode 8. In 
the annealing process, the materials of layers 10 and 14 may interdiffuse 
with the materials of layer 12 forming interface layers 11 and 15, 
respectively. The size of the devices 17A, 17B, etc. is greatly 
exaggerated in FIG. 4. Each device 17A, 17B, etc. may be tested by 
connecting one lead of the test device to the platinum electrode layer 8 
and contacting the other electrode layer 16 of the particular device 17A, 
17B, etc. with a fine probe connected to the other lead of the test 
device. Devices having the cross-sectional structure of FIG. 6 are 
similarly fabricated except that the two buffer layers 10, 12 are not 
deposited. That is, the wafer of FIG. 6 includes a silicon substrate 22, a 
silicon dioxide layer 24, an optional titanium layer 26, a first platinum 
electrode 28, a metal oxide layer 30, and a second platinum electrode 32. 
The wafer 20 is similarly pattered to form capacitor devices of various 
sizes having the cross-section shown in FIG. 6. The capacitor 40 of FIG. 7 
includes a silicon substrate 42, a silicon dioxide insulating layer 43, a 
titanium adhesion layer 44, a titanium nitride barrier layer 45, a 
platinum first electrode 45, a layer of metal oxide 48, and a platinum 
second electrode 49. The fabrication of exemplary devices of the types 
shown in FIGS. 4 through 7 will be described in detail in the examples 
below. 
FIG. 8 shows an example of the integration of a thin film metal oxide 60 
according to the invention into a DRAM memory cell 50 to form an 
integrated circuit 70 such as may be fabricated using the invention. The 
memory cell 50 includes a silicon substrate 51, field oxide areas 54, and 
two electrically interconnected electrical devices: a transistor 71 and a 
capacitor 72. Transistor 71 includes a gate 73, a source 74, and a drain 
52. Capacitor 72 includes first electrode 58, metal oxide thin film 60, 
and second electrode 77. Capacitor 72 may either be a ferroelectric 
switching capacitor, in which case metal oxide 60 would be a 
ferroelectric, or a normal capacitor, in which case metal oxide 60 would 
be a dielectric and may or may not be ferroelectric. Insulators, such as 
56, separate the devices 71, 72, except where drain 52 of transistor 71 is 
connected to first electrode 58 of capacitor 72. Electrical contacts, such 
as 55 and 78 make electrical connection to the devices 71, 72 to other 
parts of the integrated circuit 70. Electrode 58 will as well as the other 
conducting layers will generally be multilayered conductors including 
adhesion and barrier layers as is well-known in the art. 
From the above it can be seen that in the case of the wafer 1 of FIG. 5, 
when considering the deposition of buffer layer 10, the substrate 18 
referred to in step P7 (FIG. 2) comprises layers 2, 4, 6, and 8. In the 
case of the deposition of layer 30 of wafer 20 of FIG. 6, the substrate 38 
comprises layers 22, 24, 26, and 28. And in the case of the integrated 
circuit 70 of FIG. 7, the substrate 75 comprises layers 51, 54, 56, and 
58. Returning to FIG. 2, the final precursor liquid is applied to the 
substrate 18, 38, 75. The application may be by a misted deposition 
process as described in U.S. patent application Ser. No. 993,380, though 
other methods of applying a liquid to a substrate may be used. The 
precursor on the substrate is then treated, to form a solid metal oxide 
thin film. Generally it is treated by heating, but as described in U.S. 
patent application 993,380, it may also be by exposing the substrate and 
precursor to a vacuum. In the preferred embodiment, the precursor is 
treated by drying and annealing. Then the device 1, 20, 70 is completed. 
The steps P7 through P10 are generally known in the art, and thus will not 
be discussed in detail here, although some examples will be given below. 
A term that is used frequently in this disclosure is "stoichiometry" or 
"stoichiometric". As used herein, the term stoichiometric generally 
expresses a relationship between the final precursor solution and the 
desired metal oxide film 30. A "stoichiometric precursor" is one in which 
the relative proportions of the various metals in the precursor is the 
same as the proportion in a homogeneous specimen of the intended metal 
oxide thin film 30. This proportion is the one specified by the formula 
for the metal oxide thin film 30. When we say that the process permits one 
to better control the stoichiometry, we mean that the process permits one 
to better control the proportion of the various elements in the metal 
oxide film 30. 
2. Detailed Description of Exemplary Embodiments 
Turning now to a more detailed description of the invention, examples of 
precursors according to the invention and processes according to the 
invention for utilizing the precursors are given below. All processes were 
performed at the atmospheric pressure in Colorado Springs, Colo., except 
where otherwise noted. An exemplary flow chart illustrating the process 
according to the invention for preparing the first precursor example, a 
final precursor for fabricating a barium strontium titanate (BST) thin 
film, is shown in FIG. 3. 
EXAMPLE 1 
Barium Strontium Titanate (BST)--Ba.sub.0.7 Sr.sub.0.3 TiO.sub.3 
Referring to FIG. 3, in step P30 the compounds shown in Table I were 
measured. 
TABLE I 
______________________________________ 
Compound FW g mmole Equiv. 
______________________________________ 
Barium 137.327 9.4255 68.635 
0.69986 
2-ethylhexanoic 
144.21 19.831 137.51 
1.4022 
acid 
Strontium 87.62 2.5790 29.434 
0.30014 
2-ethylhexanoic 
1.44.21 8.5005 88.945 
0.6010 
acid 
Titanium 284.26 27.878 98.072 
1.0000 
Isopropoxide 
______________________________________ 
In the above table and the tables below, "FW" indicates formula weight, "g" 
indicates grams, "mmoles" indicates millimoles, and "Equiv." indicates the 
equivalent number of moles in solution. In the preferred embodiment of 
step P31 the barium is placed in 100 ml (milliliters) of 2-methoxyethanol, 
the 2-ethylhexanoic acid is added and the mixture is allowed to react 
while stirring. The step may also be preformed by placing the barium in 
the 2-methoxyethanol, allowing it to react, adding the 2-ethylhexanoic 
acid, and stirring while it reacts. In either case the reaction may be 
described by the following equation: 
(4) Ba+HO.sub.2 C.sub.8 H.sub.15 +HOC.sub.2 H.sub.4 OCH.sub.3 
.fwdarw.Ba(O.sub.2 C.sub.8 H.sub.15).sub.x (OC.sub.2 H.sub.4 
OCH.sub.3).sub.y +H.sub.2, 
where HO.sub.2 C.sub.8 H.sub.15 is 2-ethylhexanoic acid, HOC.sub.2 H.sub.4 
OCH.sub.3 is 2-methoxyethanol, (O.sub.2 C.sub.8 H.sub.15) is the 
carboxylate ligand, (OC.sub.2 H.sub.4 OCH.sub.3) is the alkoxide ligand, 
and x and y indicate the number of each ligand that is bonded to the 
barium. Usually, both x and y are approximately 1. H.sub.2, hydrogen gas, 
is a by-product of the reaction and escapes from the solution. The 
reaction of the barium heats the solution. While the solution is still 
hot, the strontium is added in step P32 and allowed to react. The heat in 
solution from the barium reaction assists the strontium reaction. When the 
strontium is all reacted, then, in step P33, the second measure of 
2-ethylhexanoic acid is added and, while stirring, the solution is heated 
to a maximum temperature of 115.degree. C. This ensures that any water 
present is distilled out. This is believed to result in a similar reaction 
to that of equation (4) except that Sr replaces Ba. 
In addition to the above reactions which produce metal-alkoxocarboxylates, 
reactions such as: 
(5) M(OR).sub.n +nHO.sub.2 C.sub.8 H.sub.15 +heat.fwdarw.M(O.sub.2 C.sub.8 
H.sub.15).sub.n +nHOR, 
where M is a metal, R is the alkyl group, n is an integer, M(OR).sub.n is 
the alkoxide, HO.sub.2 C.sub.8 H.sub.15 is 2-ethylhexanoic acid, M(O.sub.2 
C.sub.8 H.sub.15).sub.n is a metal 2-ethylhexanoate, and HOR is an 
alcohol, which reactions completely transform the alkoxide part of the 
intermediate metal-alkoxocarboxylate to full carboxylates, also occur. 
However, it is believed that the complete substitution of the alkoxides by 
the carboxylates, as previously thought, does not occur with the 
parameters as disclosed herein. Full substitution of the carboxylates 
requires significantly more heating, and even then may not readily occur. 
The mixture is then allowed to cool, and in step P34 the titanium 
isopropoxide is added followed by the addition of enough 2-methoxyethanol 
in step P35 to make 220 ml total solution. The solution is then heated and 
stirred with the following reactions: 
(6) Ba(O.sub.2 C.sub.8 H.sub.15).sub.1 (OC.sub.2 H.sub.4 OCH.sub.3).sub.1 
+Ti(OCH CH.sub.3 !.sub.2).sub.4 +heat.fwdarw.(H.sub.15 C.sub.8 
O.sub.2)Ba--O--Ti (OCH CH.sub.3 !.sub.2).sub.3 +H.sub.3 COC.sub.2 H.sub.4 
OCH(CH.sub.3).sub.2, and 
(7) Ba(O.sub.2 C.sub.8 H.sub.15).sub.1 (OC.sub.2 H.sub.4 OCH.sub.3).sub.1 
+Ti (OCH CH.sub.3 !.sub.2).sub.4 +heat.fwdarw.(H.sub.3 COC.sub.2 H.sub.4 
O)Ba--O--Ti(OCH CH.sub.3 !.sub.2).sub.3 +H.sub.15 C.sub.8 O.sub.2 
CH(CH.sub.3).sub.2 
where Ti (OCH CH.sub.3 !.sub.2).sub.4 is titanium isopropoxide, H.sub.3 
COC.sub.2 H.sub.4 OCH(CH.sub.3).sub.2 is 2-methoxy-ethoxy-isopropyl ether, 
and H.sub.15 C.sub.8 O.sub.2 CH(CH.sub.3).sub.2 is isopropyl 
2-ethylhexanoate, an ester. Similar reactions occur for the strontium. 
The ethers and some esters can be smelled during this reaction. The ethers 
are low boiling point liquids and generally boil out of solution while the 
esters are higher boiling point liquids which tend to remain in solution. 
During the heating, the maximum temperature is 116.degree. C. which also 
ensures that all isopropanol and water will be boiled out. The solution is 
then diluted to 200 ml total solution with additional 2-methoxyethanol in 
step 36. The result is a final BST precursor of 0.490 Moles concentration 
with the ratio of barium to strontium equal to 0.69986:0.30014. 
The BST precursor solution made above was utilized to fabricate a capacitor 
as shown in FIG. 7. The capacitor was fabricated by forming the silicon 
dioxide 43 by thermal oxidation in a furnace, followed by sputter 
deposition of the titanium, titanium nitride, and platinum layers 44, 45, 
and 46 respectively, to form the substrate 47. The BST precursor solution 
was then utilized to apply a layer 48 of BST of about 140 nm (nanometers) 
thick in the BST coat process P37. The BST was annealed in an oxygen 
furnace at 750.degree. C. Then electrode 49 was deposited by sputtering. 
Further details of the deposition process may be found in Copending U.S. 
patent application Ser. No. 08/165,113. The dielectric constant of the BST 
film 48 was measured to be about 490, the leakage current of the capacitor 
40 was approximately 2.times.10.sup.-9 Amps/cm.sup.2 under a voltage of 
approximately 3.3 volts, and a TDDB characteristic curve showed the life 
time to breakdown to be over 100 years under a stress of 5 volts. The 
grain size of the BST layer 48 was about 40 nm. These results indicate 
that the precursor and process of making the precursor may be used to 
yield BST thin films of much higher quality than in the prior art. The 
size of the dielectric constant, the low leakage current at voltages used 
in state-of-the-art integrated circuits, and the TDDB characteristics all 
indicate that a BST film 60 (FIG. 8) should have superior performance in 
an integrated circuit, such as that shown in FIG. 8. 
EXAMPLE 2 
Bismuth Titanate Between Buffer Layers of Strontium Titanate--SrTiO.sub.3 
/Bi.sub.4 Ti.sub.3 O.sub.12 /SrTiO.sub.3 
The compounds shown in Table II were measured. 
TABLE II 
______________________________________ 
Compound FW g mmole Equiv. 
______________________________________ 
Bismuth 2- (638.61) 21.2578 24.6328 
4.00000 
ethylhexanoate 
Titanium 284.26 5.2517 18.4750 
3.00006 
Isopropoxide 
Strontium 87.62 2.8023 31.982 
1.0000 
2-ethylhex-anoic 
144.21 9.2283 63.992 
2.00019 
acid 
Titanium 284.26 9.0912 31.982 
1.0000 
Isopropoxide 
______________________________________ 
In the above table and the tables below, bismuth 2-ethylhexanoate indicates 
a commercially available bismuth solution of bismuth 2-ethylhexanoate in 
74% naphtha; the formula weight in this case is placed in parenthesis to 
indicate that it is an equivalent formula weight of bismuth in the 
solution as a whole, rather than the formula weight of the just the 
bismuth 2-ethylhexanoate, in order to take into account the presence of 
the naphtha. The bismuth 2-ethylhexanoate was placed in 90 ml xylenes. 
Here and where used below, "xylenes" indicates a commercially available 
xylene solution which includes the three different isomers of xylene. The 
solution was stirred and heated to a maximum temperature of 117.degree. C. 
to distill out all light hydrocarbon fractions and water. The first 
measure of titanium isopropoxide was combined with 60 ml of 
2-methoxyethanol, and was stirred and heated to a maximum temperature of 
116.degree. C. to distill out all water and isopropanol. The bismuth 
solution and the titanium solution were combined, then heated to a maximum 
temperature of 136.degree. C. to distill out all 2-methoxyethanol and some 
xylenes until 60 ml of solution remained. The concentration was 0.1206 
moles of Bi.sub.4 Ti.sub.3 O.sub.12 per liter with 0.002% excess titanium. 
The strontium was placed in the 2-ethylhexanoic acid together with 50 ml 
2-methoxyethanol. The solution was stirred and heated to a maximum 
temperature of 115.degree. C. to distill off all light hydrocarbon 
fractions and water and to produce a strontium-alkoxocarboxylate as 
discussed above. Also, as discussed above, the strontium could be reacted 
with the 2-methoxyethanol first and then add the 2-ethylhexanoic acid 
after the initial reaction has taken place. The second measure of titanium 
isopropoxide was dissolved in 50 ml methoxyethanol and stirred and heated 
to a maximum of 115.degree. C. to distill off the isopropanol and water. 
The strontium and titanium solutions were combined and stirred and heated 
to a maximum temperature of 125.degree. C. to distill down to a volume of 
60.0 ml. This created a mixture of XSr--O--TiA and ASr--O--TiA structures 
as discussed above as well as some full carboxylates. The concentration 
was 0.533 moles of SrTiO.sub.3 per liter. Just prior to use, a xylene 
exchange was performed by adding 25 ml of xylenes to 5 ml of the above 
SrTiO.sub.3 solution and stirred and heated to a maximum temperature of 
128.degree. C. to distill out 7 ml to produce a final solution of 23 ml 
(milliliter) volume and a concentration of 0.116 moles of SrTiO.sub.3 per 
liter. 
A substrate 18 (FIG. 5) was baked at 140.degree. C. in air for 30 minutes 
to dehydrate it. An eyedropper was used to place 1 ml of the SrTiO.sub.3 
solution on the substrate 18, which was then spun at 1500 RPM for 20 
seconds. The wafer 1 was then placed on a hot plate and baked at 
250.degree. C. in air for four minutes. An eyedropper was used to place 1 
ml of the Bi.sub.4 Ti.sub.3 O.sub.12 solution on the wafer and the wafer 
was spud at 1500 RPM for 20 seconds. The wafer was placed on a hot plate 
and baked at 250.degree. C. for 4 minutes. The steps from using an 
eyedropper to deposit 1 ml of SrTiO.sub.3 solution on the wafer through 
baking on the hot plate were repeated for another SrTiO.sub.3 layer 14. 
The wafer was then transferred to a diffusion furnace and annealed at 
700.degree. C. in an oxygen flow of 5 l/m (liters/minute) for 50 minutes. 
The top layer 16 of 2000 .ANG. platinum was sputtered, a resist was 
applied, followed by a standard photo mask process, an ion mill etch, an 
IPC strip and a final contact anneal at 700.degree. C. in an oxygen flow 
of 5 l/m for 50 minutes. Hysteresis and switching fatigue tests, as 
described in U.S. patent application Ser. No. 07/981,133, were performed 
on the sample, and the results indicated that at the interface of the 
layers 10 and 14 and the layer 12 thin layers of strontium bismuth 
titanate 11 and 15 was formed, which strontium bismuth titanate exhibited 
very low fatigue, having a polarizability that remained almost unchanged 
all the way out past 10.sup.9 cycles. 
EXAMPLE 3 
Strontium Bismuth Tantalate--SrBi.sub.2 Ta.sub.2 O.sub.9 
The compounds shown in Table III were measured. The strontium was combined 
with the first measure of 2-ethylhexanoic acid and 80 ml 2-methoxyethanol. 
The mixture was stirred on low heat of between about 70.degree. C. and 
90.degree. C. to hurry the reaction rate. When all the strontium was 
TABLE III 
______________________________________ 
Compound FW g mmole Equiv. 
______________________________________ 
Tantalum ethoxide 
406.26 4.9553 12.197 
2.0000 
2-ethylhexanoic 
144.21 8.7995 61.019 
10.006 
acid 
Strontium 87.62 0.5330 6.0831 
0.9975 
2-ethylhexanoic 
144.21 1.7613 12.213 
2.0026 
acid 
Bismuth 2- (862.99) 10.525 12.196 
1.9998 
ethylhexanoate 
______________________________________ 
reacted and the solution had cooled to approximately room temperature, the 
tantalum ethoxide followed by the second measure of 2-ethylhexanoic acid 
were added. The mixture was stirred and heated to a maximum temperature of 
115.degree. C. Then 75 ml xylenes followed by the bismuth 2-ethylhexanoate 
were added. The solution was stirred and heated with a maximum temperature 
of about 125.degree. C. until only 60.0 ml of solution remained. The 
concentration was 0.102 moles of SrBi.sub.2 Ta.sub.2 O.sub.9 per liter. A 
substrate 38 (FIG. 6) was baked at 140.degree. C. in air for 30 minutes to 
dehydrate it. An eyedropper was used to place 1 ml of the SrBi.sub.2 
Ta.sub.2 O.sub.9 solution on the substrate 38, which was then spun at 1500 
RPM for 20 seconds. The wafer 1 was then placed on a hot plate and baked 
at above 250.degree. C. in air for three minutes. The steps from using an 
eyedropper to deposit solution on the wafer through baking on the hot 
plate were repeated for another layer. The wafer was then transferred to a 
diffusion furnace and annealed at 750.degree. C. in an oxygen flow of 5 
liters/minute for 2 hours. The top layer 32 of 2000 .ANG. platinum was 
sputtered, a resist was applied, followed by a standard photo mask 
process, an ion mill etch, an IPC strip and a final contact anneal at 
750.degree. C. in an oxygen flow of 5 l/m for 30 minutes. The resulting 
sample was tested via hysteresis curves and demonstrated almost no fatigue 
over 10.sup.10 cycles. Moreover the hysteresis curves were very boxy and 
vertical, yielding large polarizability. These results are phenomenal when 
compared to the prior art materials, and indicate that the precursors and 
process of the invention should yield excellent integrated circuits. 
EXAMPLE 4 
Strontium Bismuth Niobate--SrBi.sub.2 Nb.sub.2 O.sub.9 
The compounds shown in Table IV were measured. 
TABLE IV 
______________________________________ 
Compound FW g mmole Equiv. 
______________________________________ 
strontium 87.62 0.5625 6.4198 
1.0000 
2-ethylhex- 
144.21 2.0940 14.520 
2.2618 
anoic acid 
bismuth 2- (862.99) 11.079 12.838 
1.9998 
ethylhexanoate 
niobium 458.48 5.8862 12.839 
1.9999 
butoxide 
2-ethylhex- 
144.21 9.2911 64.428 
10.036 
anoic acid 
______________________________________ 
The strontium was placed in 30 ml 2-methoxyethanol. The first measure of 
2-ethylhexanoic acid was added and was allowed to react completely. The 
bismuth 2-ethylhexanoate was added, followed by 35 ml xylenes. The niobium 
butoxide and second measure of 2-ethylhexanoic acid was added, followed by 
40 ml of xylenes. The mixture was heated and stirred, with a maximum 
temperature of 123.degree. C., until all the butanol, water, and 
2-methoxyethanol were removed. The final volume was 63 ml, and the final 
mass was 57.475 g. The concentration was 0.102 moles of SrBi.sub.2 
Nb.sub.2 O.sub.9 per liter, or 0.1117 mmoles of SrBi.sub.2 Nb.sub.2 
O.sub.9 per gram of solution. A capacitor 20 as shown in FIG. 6 was 
fabricated utilizing this precursor for the layer 30 in a process similar 
to that of Example 3. The sample was tested and again showed low fatigue 
and excellent polarizability. 
EXAMPLE 5 
Strontium Bismuth Tantalum Niobate--SrBi.sub.2 TaNbO.sub.9 
The compounds shown in Table V were measured. 
TABLE V 
______________________________________ 
Compound FW g mmole Equiv. 
______________________________________ 
strontium 87.62 0.5821 6.6535 
1.0001 
2-ethylhex- 
144.21 1.9770 13.709 
2.0635 
anoic acid 
bismuth 2- (862.99) 11.4687 13.289 
2.0005 
ethylhexanoate 
tantalum 546.522 3.6303 6.6426 
1.0000 
butoxide 
niobium 458.48 3.0456 6.6428 
1.0000 
butoxide 
2-ethylhex- 
144.21 9.6081 66.626 
10.030 
anoic acid 
______________________________________ 
The strontium was placed in 30 ml of 2-methoxyethanol and the first measure 
of 2-ethylhexanoic acid was added and allowed to react completely. Then 
the bismuth 2-ethylhexanoate was added followed by 40 ml xylenes. The 
tantalum butoxide and the niobium butoxide were added, followed by the 
second portion of the 2-ethylhexanoic acid and 40 ml additional xylenes. 
The mixture was stirred and heated to a maximum temperature of 122.degree. 
C. until 65 ml of solution remained. The concentration was 0.102 moles of 
SrBi.sub.2 TaNbO.sub.9 per liter. A capacitor 20 as shown in FIG. 6 was 
fabricated in a process similar to that described in Example 3 utilizing 
the precursor to produce a SrBi.sub.2 TaNbO.sub.9 film 30. The resulting 
sample was tested and showed a little more fatigue than the samples of 
Examples 3 and 4 above, but still only about 5% fatigue over 10.sup.9 
cycles, which is ten times better than even the best materials in the 
prior art. The results show that SrBi.sub.2 TaNbO.sub.9 made by the 
process according to the invention should provide non-volatile 
ferroelectric memory cells 70 (FIG. 8) that last indefinitely. 
EXAMPLE 6 
Barium Bismuth Tantalate--BaBi.sub.2 Ta.sub.2 O.sub.9 
The compounds shown in Table VI were measured. 
TABLE VI 
______________________________________ 
Compound FW g mmole Equiv. 
______________________________________ 
barium 137.327 0.9323 6.7889 
1.0000 
2-ethylhex- 
144.21 1.9733 13.684 
2.0156 
anoic acid 
bismuth 2- (862.99) 11.717 13.577 
1.9999 
ethylhexanoate 
tantalum 546.522 7.4211 13.579 
2.0002 
butoxide 
2-ethylhex- 
144.21 9.9216 68.800 
10.134 
anoic acid 
______________________________________ 
The barium was placed in 40 ml of 2-methoxyethanol and 20 ml of toluene, to 
slow the reaction, and the first measure of 2-ethylhexanoic acid were 
added and allowed to react completely. Then the bismuth 2-ethylhexanoate 
was added followed by 40 ml xylenes. The solution was stirred and heated 
to a maximum temperature of about 123.degree. C. The solution was allowed 
to cool to room temperature, then the tantalum butoxide was added, 
followed by the second portion of the 2-ethylhexanoic acid and 40 ml 
additional xylenes. The mixture was heated to a temperature of about 
123.degree. C. while stirring until 66 ml of solution remained. The 
concentration was 0.103 moles of BaBi.sub.2 Ta.sub.2 O.sub.9 per liter. A 
capacitor 20 as shown in FIG. 6 was fabricated in a process similar to 
that described in Example 3 utilizing the precursor to produce a 
BaBi.sub.2 Ta.sub.2 O.sub.9 thin film 30. The BaBi.sub.2 Ta.sub.2 O.sub.9 
was not a switching ferroelectric, but was a paraelectric with a 
dielectric constant of 166 at 1 megahertz. This is a very high dielectric 
constant as compared to the dielectric constant of 3.9 for silicon 
dioxide, the most commonly used dielectric in integrated circuits. The 
leakage current was negligible, of the order of 10.sup.-8 amps/cm2 over 
the range of voltages uses in conventional integrated circuits, i.e. 1-10 
volts. The thickness of this sample was about the same thickness generally 
used for dielectrics in conventional integrated circuits. These results 
show that this material will be an excellent high dielectric material in 
integrated circuits. 
EXAMPLE 7 
Lead Bismuth Tantalate--PbBi.sub.2 Ta.sub.2 O.sub.9 
The compounds shown in Table VII were measured. 
TABLE VII 
______________________________________ 
Compound FW g mmole Equiv. 
______________________________________ 
Lead 2-ethyl- 
(1263.6) 16.691 13.209 
1.1000 
hexanoate in 
xylenes 
bismuth 2- (753.35) 18.095 24.019 
2.0002 
ethylhexanoate 
tantalum 546.52 13.126 24.017 
2.0001 
butoxide 
2-ethylhex- 
144.21 17.967 124.59 
10.375 
anoic acid 
______________________________________ 
The lead 2-ethylhexanoate in xylenes previously prepared stock solution and 
the bismuth 2-ethylhexanoate were combined, followed by 40 ml xylenes. 
Then the tantalum butoxide was added, followed by the 2-ethylhexanoic 
acid. The mixture was stirred on low heat of between about 70.degree. C. 
and 90.degree. C. for four hours, then raised to a maximum temperature of 
114.degree. C. until 66 ml of solution remained. The concentration was 
0.172 moles of PbBi.sub.2 Ta.sub.2 O.sub.9 per liter with 10% excess lead. 
A capacitor 20 as shown in FIG. 6 was fabricated in a process similar to 
that described in Example 3 utilizing the precursor to produce a thin film 
30. The sample was tested and proved to have a dielectric constant of 114 
at 1 megahertz and small leakage current. 
EXAMPLE 8 
Barium Bismuth Niobate--BaBi.sub.2 Nb.sub.2 O.sub.9 
The compounds shown in Table VIII were measured. 
TABLE VIII 
______________________________________ 
Compound FW g mmole Equiv. 
______________________________________ 
barium 137.327 0.9419 6.8588 
1.0000 
2-ethylhex- 
144.21 2.0538 
anoic acid 
bismuth 2- (862.99) 11.838 13.717 
1.9999 
ethylhexanoate 
niobium 458.48 6.2894 13.718 
2.0001 
butoxide 
2-ethylhex- 
144.21 10.051 69.697 
10.162 
anoic acid 
______________________________________ 
The barium was placed in 30 ml of 2-methoxyethanol and 20 ml of toluene, to 
slow the reaction, and the first measure of 2-ethylhexanoic acid was added 
and allowed to react completely while stirring. Then the bismuth 
2-ethylhexanoate was added followed by 50 ml xylenes. The mixture was 
stirred and heated with a maximum temperature of 118.degree. C. The 
solution was allowed to cool to room temperature, then the niobium 
butoxide was added, followed by the second portion of the 2-ethylhexanoic 
acid and 30 ml additional xylenes. The mixture was heated to a temperature 
of 124.degree. C. while stirring until 68 ml of solution remained. The 
concentration was 0.101 moles of BaBi.sub.2 Nb.sub.2 O.sub.9 per liter. A 
capacitor 20 as shown in FIG. 6 was fabricated in a process similar to 
that described in Example 3, utilizing the precursor to produce a thin 
film 30. The sample was tested and proved to have a dielectric constant of 
103.46 and good leakage current results. 
In the discussions below, we shall use barium titanate, BaTiO.sub.3 and 
barium strontium titanate, BaSrTiO.sub.3, as an exemplary metal oxides. 
However, it should be understood that the discussion could also be made in 
terms of other metal oxides. The most commonly used liquid organic method 
of fabricating metal oxides prior to this invention was the sol-gel 
process. In the sol-gel process for barium titanate, barium and titanium 
alkoxides are mixed in organic solvents to form precursors. Barium may 
also may also be reacted with titanium alkoxide dissolved in alcohol. 
Despite the fact that such precursors are not stable enough for commercial 
manufacturing processes, the present inventors and their colleagues have 
studied them extensively and some of the results are of general 
importance. 
In contrast to the general view that a bi-metallic oxide, such as 
BaTi(OR).sub.6 where R is the isopropyl radical i-Pr, is the precursor of 
the oxide phase in solution, we have discovered that the above-mentioned 
oxoalkoxides, such as BaTiO.sub.x (OR).sub.6-2x, which are formed in the 
solutions complex does not exist in the sol-gel precursor solutions. It is 
the and are the true precursors for the complex oxide BaTiO.sub.3. The 
chemical reactions which lead to the formation of these oxoalkoxides are 
numerous. We have isolated a series of such complexes in the form of 
single crystals and solved their structures. For example, one such crystal 
had the structure BaTiO(OPr-i).sub.4.i-PrOH. In such a structure a 
Ba--O--Ti core already exists which is preserved in all stages of 
preparation of BaTiO.sub.3 from this precursor. It is noteworthy that the 
higher the x value the better are the conditions for formation of 
BaTiO.sub.3. 
On the other hand, for commercial or other out-of-the-laboratory 
applications, it is more convenient to use carboxylates as precursors 
since they are far more stable to hydrolysis, therefore the properties of 
the prepared solutions do not change over time in storage. Such 
carboxylate solutions are also more convenient for processing in terms of 
ability to dilute or concentrate to an appropriate concentration and 
viscosity to form a film of the desired density and thickness. In a series 
of papers, representative ones of which are referenced above, Vest and his 
colleagues at Purdue University have studied fabrication methods utilizing 
carboxylate precursors in general and the fabrication of BaTiO.sub.3 using 
such precursors in particular. A the first stage in the process, Vest 
suggested preparation of neodecanoates as follows: 
(8) NH.sub.4 OH+C.sub.9 H.sub.19 COOH.fwdarw.C.sub.9 H.sub.19 COONH.sub.4 
+H.sub.2 O, and 
(9) 2C.sub.9 H.sub.19 COONH.sub.4 +BaCl.sub.2 .fwdarw.2NH.sub.4 Cl+(C.sub.9 
H.sub.19 COO).sub.2 Ba 
Barium carboxylate is then extracted by xylenes. For titanium, a partially 
substituted alkoxide derivative was prepared by refluxing titanium 
methoxide, neodecanoic acid, and methanol to produce the following 
reaction: 
(10) Ti(OCH.sub.3).sub.4 +2C.sub.9 H.sub.19 COONH.fwdarw.(C.sub.9 H.sub.19 
COO).sub.2 Ti(OCH.sub.3).sub.2 +2CH.sub.3 OH, 
with subsequent distilling off of the excess CH.sub.3 OH. The Ba and Ti 
derivatives were then combined in xylene at room temperature to form the 
final precursor used for fabrication of BaTiO.sub.3. Vest coined the term 
"MOD" solutions for such precursors from the fact that after deposition 
the metal-organics in solution decompose during the drying and annealing 
processes to form the desired complex metal oxides. The decomposition 
during the drying and annealing lead to inferior quality films. For 
example, the carboxylates go through a carbonate stage during the drying 
and annealing before forming the metal oxide. This can result in some 
carbonate residue remaining in the final films even after oxygen 
annealing. Such decompositions make it practically impossible to use the 
MOD precursors in chemical vapor deposition processes, since the carbon 
residue coats the substrate. 
Turning now to the process of the invention, and using Example 1 above as 
the exemplary process, barium metal is dissolved in a mixture of 
2-ethylhexanoic acid and methoxyethanol, which leads to the 
alkoxycarboxylate: 
(11) Ba+2C.sub.8 H.sub.15 O.sub.2 H+CH.sub.3 OC.sub.2 H.sub.4 
OH.fwdarw.Ba(OC.sub.2 H.sub.4 OCH.sub.3).sub.x (C.sub.8 H.sub.15 
O.sub.2).sub.2-x 
where the x value may be 1 or 2. The solution is clear, the brown-red 
typical of barium methoxyethoxide solutions being absent. However, this 
does not exclude the formation of barium methoxyethoxide. It only means 
that the radicals with conjugated bonds which are formed in the process of 
alkaline oxidation of methoxyethoxide are destroyed in the acidic medium. 
After the addition of the strontium, additional 2-ethylhexanoic acid, 
titanium isopropoxide, and 2-methoxyethanol leads to complex formation 
immediately, and the subsequent thermal treatment, results in a series of 
chemical reactions including: 
(12) Ti(OPr-i).sub.4 +xC.sub.8 H.sub.15 O.sub.2 H.fwdarw.Ti(O.sub.2 C.sub.8 
H.sub.15).sub.x (OPr-i).sub.4-x +xi-PrOH. 
The complete substitution of alkoxide groups by carboxylates never occurs, 
which leaves excess 2-ethylhexanoic acid in solution, which takes part in 
the following reactions: 
(13) C.sub.8 H.sub.15 O.sub.2 H+ROH&lt;--&gt;C.sub.8 H.sub.15 O.sub.2 R+H.sub.2 
O, and 
(14) ROH+R'OH&lt;--&gt;ROR'+H.sub.2 O, 
where R=i-Pr, and R'=CH.sub.3 OC.sub.2 H.sub.4. These reactions result in a 
gradual elimination of organics from the solution. The different products 
in the solution during the thermal treatment process is difficult to 
pinpoint since the process is an on going one, but the fact that a series 
of products forms is indicated by the gradual and very slow increase of 
temperature from 79.degree. C. to 116.degree. C. with many steps in 
temperature in the course of distilling off the organics from the 
solution. The water that is formed, even if formed in traces, reacts with 
the alkoxides to form oxoalkoxides, which are believed to be some of the 
products formed during the thermal treatment process. It is important in 
the process that the thermal treatment and distillation is performed on 
the complex solution containing all the metals of the final desired 
compound, since this insures the metal complex formation in solution. 
Thus, the true final precursor may be represented as a metal complex such 
as M.sub.1 M.sub.2 O.sub.x (OR).sub.y-2x (C.sub.8 H.sub.15 COO).sub.4-y, 
where M.sub.1 represents one metal and M.sub.2 represents a second metal. 
In the example of barium titanate, the true final precursor may be 
represented as BaTiO.sub.x (OR).sub.y-2x (C.sub.8 H.sub.15 COO).sub.4-y. 
Such complexes contain all or most of the metal-oxygen-metal bonds 
necessary for complex oxide formation on deposition and drying of the 
final precursor, and in addition the presence of carboxylates preserves 
the final precursor solution from quick hydrolysis. Thus the result is a 
final precursor solution that has both the properties of the sol-gels of 
producing excellent films, and the properties of the MODs of being stable 
over sufficient periods to enable incorporation into routine manufacturing 
processes for commercial use. 
A feature of the invention is that it uses metal alkoxycarboxylates rather 
than carboxylates as the initial or intermediate precursor for many 
metals, and generally also includes alkoxycarboxylates in the final 
precursor. Another feature of the invention is that in the case of the 
metal titanium, the isopropoxide is used as the initial precursor, which 
eliminates the step of titanium alkoxycarboxylate isolation. 
Another feature of the invention is that chemical reactions that occur in 
the precursor preparation stage differ markedly from those of the prior 
art. These different chemical reactions make an enormous difference in the 
chemical nature of the final precursor. 
A further feature of the invention is the considerable thermal treatment of 
the combined initial precursors, with complex metal-oxygen-metal bonds 
being formed during this treatment and thus being present in solution 
prior to application of the solution to the substrate. 
A related feature of the invention is that the complex metal oxide, such as 
BaTiO.sub.3, is formed in one step during the application, drying and 
heating processes, rather than the precursor compound going through the 
carbonate stage, such as BaCO.sub.3 +TiO.sub.2, which requires further 
thermal treatment after deposition to result in the metal oxide, such as 
BaTiO.sub.3. As a result the metal oxides produced by the process of the 
invention are microscopically homogeneous and of the high quality 
necessary in integrated circuit manufacturing processes. 
Yet a further feature of the invention is that the precursor contains 
carboxylate ligands. While the proportion of carboxylate ligands is not as 
large as in the MOD process, the amount is such that the precursor is 
stable for periods such as are common for storage of precursors in typical 
manufacturing processes, i.e. for several months. Thus the precursors and 
processes of the invention are suitable for large scale commercial 
fabrication processes. 
There has been described novel metal-alkoxocarboxylate precursors and 
processes utilizing the precursor to fabricate thin films for electronic 
device applications. It should be understood that the particular 
embodiments shown in the drawings and described within this specification 
are for purposes of example and should not be construed to limit the 
invention which will be described in the claims below. Further, it is 
evident that those skilled in the art may now make numerous uses and 
modifications of the specific embodiment described, without departing from 
the inventive concepts. For example, now that the metal-alkoxocarboxylate 
precursors have been described, such precursors can be formed by many 
different perturbations of the specific processes described in the 
examples. Further, the precursors can be combined with conventional 
processes to provide variations on the processes described. Other metals 
may be utilized to form other metal-alkoxocarboxylates. It is also evident 
that the process steps recited may in some instances be performed in a 
different order. Or equivalent structures and process may be substituted 
for the various structures and processes described. Further, now that the 
advantages of utilizing a precursor in which the metal-oxygen-metal bonds 
are already formed has been pointed out, many processes utilizing this 
concept may be devised. Consequently, the invention is to be construed as 
embracing each and every novel feature and novel combination of features 
present in and/or possessed by the precursors, precursor formation 
processes, metal oxide fabrication processes, electronic devices, and 
electronic device manufacturing methods described.