U.S. patent application number 09/855727 was filed with the patent office on 2001-12-13 for novel organic titanium compound suitable for mocvd.
This patent application is currently assigned to MITSUBISHI MATERIALS CORPORATION. Invention is credited to Itsuki, Atsushi, Ogi, Katsumi, Tachibana, Taiji, Uchida, Hiroto.
Application Number | 20010050028 09/855727 |
Document ID | / |
Family ID | 27458645 |
Filed Date | 2001-12-13 |
United States Patent
Application |
20010050028 |
Kind Code |
A1 |
Itsuki, Atsushi ; et
al. |
December 13, 2001 |
Novel organic titanium compound suitable for MOCVD
Abstract
Bis(dipivaloylmethanato)diisobutoxytitanium or
bis(dipivaloylmethanato)-di- (2,2-dimethyl-l-propoxytitanium per
se, or as used as a raw material in a MOCVD process, as is or as a
solution in an organic solvent, for example, tetrahydrofuran,
produces a dielectric thin film of a fine texture having a film
thickness which is proportional to the deposition time and the
concentration of the solution.
Inventors: |
Itsuki, Atsushi; (Saitama,
JP) ; Tachibana, Taiji; (Hyogo, JP) ; Uchida,
Hiroto; (Saitama, JP) ; Ogi, Katsumi;
(Saitama, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
MITSUBISHI MATERIALS
CORPORATION
1-5-1, ohtemachi, Chiyoda-ku
Tokyo
JP
100
|
Family ID: |
27458645 |
Appl. No.: |
09/855727 |
Filed: |
May 16, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09855727 |
May 16, 2001 |
|
|
|
09231300 |
Jan 15, 1999 |
|
|
|
Current U.S.
Class: |
106/1.22 ;
106/287.19 |
Current CPC
Class: |
C23C 16/409 20130101;
C07F 7/003 20130101; C23C 16/18 20130101 |
Class at
Publication: |
106/1.22 ;
106/287.19 |
International
Class: |
C23C 018/00; C23C
020/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 9, 1998 |
JP |
HEI 10-027241 |
Feb 9, 1998 |
JP |
HEI 10-027243 |
Mar 11, 1998 |
JP |
HEI 10-059581 |
Claims
1. An organic titanium compound represented by the general formula
Ti(DPM).sub.2(OR).sub.2 wherein DPM represents dipivaloylmethanato
and R represents an isobutyl or neopentyl group.
2. A stock solution comprising an organic titanium compound
according to claim 1 dissolved in an organic solvent.
3. The stock solution according to claim 2, wherein the organic
solvent is at least one solvent selected from the group consisting
of cyclic and acyclic alkanes, cyclic and acyclic monoethers and
diethers, alkoxyalcohols, diols, esters, and substituted and
unsubstituted pyridines.
4. The stock solution according to claim 3, wherein the organic
solvent is at least one solvent selected from the group consisting
of cyclic and acyclic alkanes having 5 to 8 carbon atoms, dioxane,
acyclic diethers having 3 to 12 carbon atoms, unsubstituted and
lower alkylsubstituted tetrahydrofurans, mono- and di-branched
alkylethers having 5 to 12 carbon atoms, alkoxyalcohols having 3 to
12 carbon atoms, diols having 2 to 4 carbon atoms, alkyl acetates
and alkyl acetoacetates wherein the alkyl has 1 to 5 carbon atoms,
pyridine, and lower alkyl-substituted pyridines.
5. The stock solution according to claim 4, wherein the organic
solvent is monomethyl- or dimethylsubstituted tetrahydrofuran.
6. A method of forming a titanate thin film comprising subjecting a
stock solution according to claim 2 to a metal-organic chemical
vapor deposition process on a substrate thereby forming said
film.
7. A method of forming a titanate thin film comprising subjecting a
stock solution according to claim 3 to a metal-organic chemical
vapor deposition process on a substrate thereby forming said
film.
8. A method of forming a titanate thin film comprising subjecting a
stock solution according to claim 4 to a metal-organic chemical
vapor deposition process on a substrate thereby forming said
film.
9. A method of forming a titanate thin film comprising subjecting a
stock solution according to claim 5 to a metal-organic chemical
vapor deposition process on a substrate thereby forming said
film.
10. A titanate thin film deposited on a substrate by a method
according to claim 6.
11. A titanate thin film deposited on a substrate by a method
according to claim 7.
12. A titanate thin film deposited on a substrate by a method
according to claim 8.
13. A titanate thin film deposited on a substrate by a method
according to claim 9.
14. A barium strontium titanate thin film deposited on a substrate
obtained by a method comprising subjecting a stock solution
comprising (1) an organic titanium compound represented by the
general formula Ti(DPM).sub.2(OR).sub.2 wherein DPM represents
dipivaloylmethanato and R represents an isobutyl or neopentyl
group, (2) a barium source, and (3) a strontium source, dissolved
in an organic solvent, to a metal-organic chemical vapor deposition
process on a substrate, thereby forming said film.
15. The barium strontium titanate thin film deposited on a
substrate according to claim 14, wherein the organic solvent is at
least one solvent selected from the group consisting of cyclic and
acyclic alkanes, cyclic and acyclic monoethers and diethers,
alkoxyalcohols, diols, esters, and substituted and unsubstituted
pyridines.
16. The barium strontium titanate thin film deposited on a
substrate according to claim 15, wherein the organic solvent is at
least one solvent selected from the group consisting of cyclic and
acyclic alkanes having 5 to 8 carbon atoms, dioxane, acyclic
diethers having 3 to 12 carbon atoms unsubstituted and lower
alkylsubstituted tetrahydrofurans, mono- and di-branched
alkylethers having 5 to 12 carbon atoms, alkoxyalcohols having 3 to
12 carbon atoms, diols having 2 to 4 carbon atoms, alkyl acetates
and alkyl acetoacetates wherein the alkyl has 1 to 5 carbon atoms,
pyridine, and lower alkyl-substituted pyridines.
17. The barium strontium titanate thin film deposited on a
substrate according to claim 16, wherein the organic solvent is
monomethyl- or dimethylsubstituted tetrahydrofuran.
18. A method of forming a titanate thin film comprising subjecting
an organic titanium compound represented by the general formula
Ti(DPM).sub.2(OR).sub.2 wherein DPM represents dipivaloylmethanato
and R represents an isobutyl or neopentyl group, to a metal-organic
chemical vapor deposition process on a substrate, thereby forming
said film.
19. The method of claim 18, wherein R is isobutyl.
20. The method of claim 18, wherein R is neopentyl.
Description
BACKGROUND OF THE INVENTION
[0001] Field of the Invention
[0002] The present invention relates to a novel organic titanium
compound that is useful as a titanium source in the production of a
metal oxide thin film containing titanium by a metal-organic
chemical vapor deposition (MOCVD) process. The present invention
also relates to a stock solution containing the compound for a
MOCVD process, and a method for forming a titanate dielectric thin
film using the stock solution. The metal oxide thin film containing
titanium is useful as not only a dielectric thin film but also as a
semiconductor thin film, an optical thin film, a surface
reinforcing film, and a thin film catalyst.
[0003] Discussion of the Background
[0004] The rapid increase in integration density of DRAMs has
required that compound oxide dielectric materials be used as
capacitors having higher dielectric constants than those of
conventional SiO.sub.2 dielectric thin films, which have been used
with great difficulty. Examples of compound oxide dielectric
materials include titanium-containing compound oxides, such as,
lead titanate (PT), lead zirconate titanate (PZT), lead lanthanum
zirconate titanate (PLZT), strontium titanate (ST), barium titanate
(BT), and barium strontium titanate (BST). Among them, BST is most
preferable in view of dielectric characteristics.
[0005] Sol-gel processes have been vigorously studied for the
production of compound oxide dielectric thin films, in which metal
alkoxide solutions are applied onto substrates by spin coating
methods. In the sol-gel processes, applied metal components are
completely used as films without evaporation; hence the
compositions of the films can be easily controlled. Capacitor
electrodes for DRAMs, however, have larger steps that have
complicated configurations with integration density. Thus, a
uniform dielectric thin film is barely formed on an electrode
substrate by a spin coat method.
[0006] For several years recently, deposition of dielectric
thin-films by MOCVD processes has been actively studied in
anticipation of a trend towards higher integration density of
semiconductor devices, since the methods have superior step
covering characteristics, that is, coating ability on complicated
surfaces having steps. Organometallic compounds as raw materials
generally used are organometallic complexes and metal alkoxides
having .beta.-diketone ligands such as dipivaloylmethane (DPM).
Alkoxide or .beta.-diketone complexes are used as sources of
metals. such as Ti, Zr, and Ta, and .beta.-diketone complexes are
also used as sources of Sr and Ba.
[0007] In the MOCVD process, a metal source is evaporated by heat
under a reduced pressure, and then the vapor is transferred into a
deposition chamber and decomposed on a substrate to deposit the
resulting metal oxide on the substrate. In the above-mentioned
compound oxide thin film, at least two types of organometallic
compounds must be used. Since these compounds have different
vaporization characteristics in the MOCVD process, control of
volumes of the compounds supplied to the deposition chamber is
significantly important for the control of the film
composition.
[0008] At the beginning of the formation of a dielectric thin film
by a MOCVD process, organometallic compounds have been directly
evaporated by heat and the formed vapor has been transferred into a
deposition chamber. The organometallic compounds and particularly
DPM complexes that have been recommended in the MOCVD process are
unstable and barely vaporizable. As a result, vaporization will be
inactivated in the operation or pyrolysis will occur prior to the
vapor of the compounds reaching the deposition chamber. Thus, it is
difficult to achieve stable transfer of the vapor of the compounds
into the deposition chamber. Expensive raw materials should be
disposed after one film deposition cycle. Furthermore, the film
composition is controlled with difficulty, resulting in unstable
supply of thin films having superior dielectric
characteristics.
[0009] In order to solve such problems, a solution feeding method
has been developed, in which a stock solution of organometallic
compounds dissolved in an organic solvent is supplied into a
vaporization chamber placed in front of a deposition chamber, and
then the vapor in the vaporization chamber is fed to the deposition
chamber for film deposition. Since DPM complexes are stable in
solution, the stock solution can be repeatedly used. Furthermore,
the heating temperature decreases due to vaporization to prevent
pyrolysis of the compounds before they reach the deposition
chamber. As a result, the film composition can be readily
controlled.
[0010] Japanese Patent Laid-Open No. 5-271253 discloses
bis(dipivaloylmethanato)-dialkoxy titanium complex
[Ti(DPM).sub.2(OR).sub.2 wherein R is lower alkyl] as an organic
titanium compound which is used as a raw material in a MOCVD
process. Only bis(dipivaloylmethanato)-diisopropoxy titanium
[Ti(DPM).sub.2(O-i-Pr).sub- .2] is disclosed as a typical example
when the R is isopropyl. Japanese Patent Laid-Open No. 9-40683
discloses bis(dipivaloylmethanato)-di-tert-b- utoxy titanium
[Ti(DPM).sub.2(O-t-Bu).sub.2] as an organic titanium compound
suitable for a solution feeding method.
[0011] In the solution feeding method, however, a low concentration
solution must be used when the solubility of the organometallic
compounds is low in the organic solvent; hence the deposition rate
significantly decreases, resulting in inefficient film deposition.
On the other hand, the use of a solution of a nearly saturated
concentration causes precipitation of the compounds during the
feeding of the stock solution due to evaporation of the solvent. As
a result, the concentration of the stock solution varies, and the
composition of the resulting film also varies. Accordingly, it is
difficult to control the film composition. Some organometallic
compounds are reactive with other organometallic compounds and/or
the solvent, resulting in a decrease in vaporization of the
compounds. As a result, it is difficult to control the film
composition, and clogging will frequently occur due to the residue
in the vaporization chamber and the coagulation in pipes and
nozzles.
[0012] Requirements for the organometallic compounds are high
solubility in an organic solvent, stable vaporization, and
inertness to the other raw compounds and the solvent before the
vaporization. Other important factors for the MOCVD process include
high vaporization characteristics at a low temperature and high
step covering characteristics over a wide temperature range from a
low temperature to a high temperature.
[0013] In the formation of BST thin films, DPM complexes, i.e.,
Ba(DPM).sub.2 and Sr(DPM).sub.2 and their adducts are exclusively
used as barium and strontium sources for the reason that any other
suitable compounds are not found. As titanium sources, titanium
alkoxide and titanium DPM complex are conventionally used, but
these have insufficient film deposition characteristics. In the
case of the formation of a BST film by a MOCVD process, titanium
functions as nuclei of the film deposition. Thus, the deposition of
barium and strontium is decelerated when the deposition of titanium
is delayed; hence the titanium compound has significant effects on
the deposition rate of the BST film.
[0014] For example, titanium alkoxides such as titanium
isopropoxide among conventional titanium sources are reactive with
Ba(DPM).sub.2 and Sr(DPM).sub.2, hence their vaporization
characteristics significantly deteriorate. DPM complex of titanium,
i.e., TiO(DPM).sub.2 is generally present as a dimer or a trimer,
and it has inferior vaporization characteristics.
[0015] Use of titanium alkoxide DPM complexes is also known. Among
such types of complexes which have been proposed, a complex having
isopropyl groups as alkoxy groups, [Ti(DPM).sub.2(O-i-Pr).sub.2],
has a low vaporization temperature; however, it can be easily
polymerized, resulting in deterioration of evaporation
characteristics and thus a significant decrease in the film
deposition rate. Another complex having n-butoxy groups as alkoxy
groups, [Ti(DPM).sub.2(O-n-Bu).sub.2] also has the same problem.
Although a complex having t-butoxy groups as alkoxy groups.
[Ti(DPM).sub.2(O-t-Bu).sub.2], shows low reactivity with
Ba(DPM).sub.2 and Sr(DPM).sub.2 in the solution, it has low
solubility in organic solvents. Thus, the film deposition rate of
this compound is also low.
SUMMARY OF THE INVENTION
[0016] It is an object of the present invention to provide an
organic titanium compound which has high solubility in organic
solvents, shows stable vaporization at a low temperature, is stable
in a vaporized state, and is capable of forming a dielectric thin
film having a readily controlled composition with a significantly
high deposition rate and superior step covering characteristics
over a wide temperature range from a low temperature to a high
temperature by either a solid supply method or a solution supply
method, when the compound is used as a raw material in a MOCVD
process.
[0017] The present inventors have discovered that titanium alkoxide
DPM complexes wherein the alkoxy group is an isobutoxy or
neopentyloxy (=2,2-dimethylpropoxy) group can solve the
above-mentioned problems. The titanium compounds are novel titanium
compounds represented by the general formula
Ti(DPM).sub.2(OR).sub.2, wherein DPM represents dipivaloylmethanato
and R represents a isobutyl or neopentyl group.
[0018] The present invention also provides a stock solution for
MOCVD comprising a solution of such an organic titanium compound
dissolved in an organic solvent, and a method for forming a
titanate thin film by MOCVD comprising the use of the stock
solution as a titanium source.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] A more complete appreciation of the invention and many of
the attendant advantages thereof will be readily obtained as the
same becomes better understood by reference to the following
detailed description when considered in connection with the
accompanying drawings, wherein:
[0020] FIG. 1 is a schematic view of a method for evaluating the
step covering characteristics.
[0021] FIG. 2 is a TG-DTA thermogram of
bis(dipivaloylmethanato)-diisobuto- xytitanium in accordance with
the present invention.
[0022] FIG. 3 is a TG-DTA thermogram of
bis(dipivaloylmethanato)-di(2,2-di- methyl-l-propoxytitanium in
accordance with the present invention.
[0023] FIG. 4 is a TG-DTA thermogram of known
bis(dipivaloylmethanato)-dii- sopropoxytitanium.
[0024] FIG. 5 is an electron microscopic photograph showing a fine
texture of a BST thin film deposited using
bis(dipivaloylmethanato)-diisobutoxyti- tanium in accordance with
the present invention as a titanium source.
[0025] FIG. 6 is an electron microscopic photograph showing a fine
texture of a BST thin film deposited using
bis(dipivaloylmethanato)-di(2,2-dimeth- yl-l-propoxytitanlum in
accordance with the present invention as a titanium source.
[0026] FIG. 7 includes electron microscopic photographs showing
fine textures of BST thin films deposited using conventional
organic titanium compounds as a titanium source; that is, FIG. 7(a)
for Ti(DPM).sub.2(O-i-Pr).sub.2 and FIG. 7(b) for
Ti(DPM).sub.2.
DETAILED DESCRIPTION OF THE INVENTION
[0027] Novel organic titanium compounds in accordance with the
present invention represented by the general formula
Ti(DPM).sub.2(OR).sub.2, wherein DPM and R are described above,
include the following two compounds:
[0028] (1) bis(dipivaloylmethanato)-diisobutoxytitanium
[0029] (2)
bis(dipivaloylmethanato)-di-(2,2-dimethyl-l-propoxytitanium)
[0030] Hereinafter, these compounds may be expressed by the
following abbreviations:
[0031] Compound (1): Ti(DPM).sub.2(O-i-Bu).sub.2
[0032] Compound (2): Ti(DPM).sub.2(O-DMPr).sub.2
(DMPr=dimethylpropyl)
[0033] These two organic titanium compounds
Ti(DPM).sub.2(O-i-Bu).sub.2 and Ti(DPM).sub.2(O-DMPr).sub.2 are
each a mixture of a cis-isomer and a trans-isomer that will be
represented by the following structural formulae. Since the
cis-isomer and the trans-isomer have very near boiling points and
melting points, these are inseparable. Thus,
bis(dipivaloylmethanato)-diisobutoxytitanium can be isolated as a
mixture of the cis-and trans-isomers. 1
[0034] In the formulae A is H or CH.sub.3. More specifically, A=H
for the compound (1), i.e.,
bis(dipivaloylmethanato)-diisobutoxytitanium or
Ti(DPM).sub.2(O-i-Bu).sub.2, and A=CH.sub.3 for the compound (2),
i.e., bis(dipivaloylmethanato)-di-(2,2-dimethyl-l-propoxytitanium)
or Ti(DPM).sub.2(O-DMPr).sub.2.
[0035] The organic titanium compounds can be directly produced by a
reaction of the corresponding tetraalkoxytitanium compounds
represented by the general formula Ti(OR).sub.4, wherein R is the
same as above [tetraisobutoxytitanium for the compound (1) or
tetra-(2,2-dimethyl-l-pro- poxy)titanium 32
tetra-neopentoxytitanium for the compound (2)] with
dipivaloylmethane (=2,2,6,6-tetramethyl-3,5-heptanedione) in an
adequate solvent. Since the tetraalkoxytitanium compounds as the
starting materials, however, are not commercially available, the
following process using commercially available products may be
employed.
[0036] The starting material used is, for example,
tetraisopropoxytitanium- . The starting material is dissolved into
an adequate solvent. Examples of preferred solvents include
aromatic hydrocarbons, such as benzene, toluene, xylene, and
mesitylene; and aliphatic hydrocarbons, such as pentane and
hexane.
[0037] Alcohol represented by the general formula ROH wherein R is
the same as above, i.e., 2-methyl-l-propanol (=isobutyl alcohol)
for the compound (1) or 2,2-dimethyl-l-propanol (=neopentyl
alcohol) for the compound (2), is added to the solution in an
amount of two times by molar ratio that of the starting material.
The solution is heated to near the boiling point or higher of the
alcohol, i.e., isopropyl alcohol, which corresponds to the alkoxy
group in the starting material, to form
diisopropoxydiisobutoxytitanium or
diisopropyldineopentyl-oxytitanium in which two isopropoxy groups
among four groups in the starting material are replaced with RO
groups. Although more isopropoxy groups may be replaced by
increasing the volume of alcohol (ROH), such excessive replacement
causes an increase in production cost since the reaction
successfully proceeds by the replacement of the two groups.
[0038] The solution is cooled to room temperature, and then two
times by molar ratio to the starting material of diplvaloylmethane
is added. The isopropoxy groups having higher reactivity are
predominantly released and dipivaloylmethane combines with
titanium. Bis(dipivaloylmethanato)-diisob- utoxytitanium or
bis(dipivaloylmethanato)-di-(2,2-dimethyl-l-propoxy)titan- ium is
thereby formed. The solution is concentrated to isolate the product
from the solution as crystal. The remaining water and OH groups are
removed from the product during the concentration process. In this
method, a mixture composed of a major amount of cis-isomer and a
minor amount of trans-isomer is generally obtained.
[0039] Removal of water contributes to an improvement in storage
stability of the product. Sr(DPM).sub.2 and Ba(DPM).sub.2 as
strontium and barium sources are highly reactive with OH groups,
vaporization characteristics of the raw materials will decrease
when such a reaction occurs. This causes some problems, that is, an
increase in the residue in the vaporization chamber, an increase in
clogging in pipes and nozzles, and difficult control of the film
composition. The removal of the OH groups by the concentration can
solve these problems in the BST film deposition.
[0040] The resulting crystal may be purified by recrystallization
or the like, if necessary. It is preferable that the purified
crystal of bis(dipivaloylmethanato)-diisobutoxytitanium or
bis(dipivaloylmethanato)-- di-(2,2-dimethyl-l-propoxy)titanium
contain 0.1 percent by weight or less of OH groups and 5 ppm or
less of residual chlorine.
[0041] Bis(dipivaloylmethanato)-diisobutoxytitanium or
bis(dipivaloylmethanato)-di-(2,2-dimethyl-l-propoxy)titanium in
accordance with the present invention is present as a monomer,
hence it has high solubility in organic solvents, is steadily
vaporized at low temperatures, and is stable in solution and vapor.
Since the product is inert to strontium sources and barium sources,
it can be used for the formation of MOCVD films by either a solid
feeding method or a solution feeding method, and the film
composition can be readily controlled. In the solution feeding
method, a highly concentrated solution can be used and pyrolysis
rapidly and completely proceeds as shown in the thermogravimetric
curves in the Examples below. As a result, a significantly high
film deposition rate can be achieved.
[0042] The resulting dielectric thin film has superior step
covering characteristics over a wider temperature range from a low
temperature to a high temperature. Since the organic titanium
compound in accordance with the present invention has stable
vaporization characteristics and stability after vaporization, the
thickness of the dielectric thin film formed by the MOCVD process
increases substantially in proportion to the deposition time. Since
the compound has high solubility and stability as a solution in a
solution feeding method, the concentration due to precipitation of
raw materials does not occur. Thus, the thickness of the dielectric
thin film increases substantially in proportion to the
concentration of the solution. Accordingly, the film thickness can
be readily controlled by the deposition time, and the concentration
of the solution in the case of the solution feeding method.
[0043] Since the film deposition rate is high and is substantially
proportional to the concentration, a dielectric thin film having a
large thickness of several thousands of manometers can be formed by
increasing the concentration of the solution in a short time, for
example, five minutes. The thickness of the dielectric film reaches
ten thousand manometers (=10 .mu.m) for a deposition time of 20
minutes or more. Accordingly, a dielectric thin film having
controlled thickness and composition can be formed for a
significantly short deposition time compared with conventional
processes.
[0044] The film deposition by MOCVD may be performed by any
conventional process. For example, in a solid supplying method,
vapor formed by heating of the raw compounds in a vaporization
chamber is fed with a carrier gas into a deposition chamber.
[0045] In the solution feeding method, organometallic compounds as
raw materials are used as a stock solution in an organic solvent.
In this case, the stock solution is a solution
bis(dipivaloylmethanato)-diisobuto- xytitanium or
bis(dipivaloylmethanato)-di-(2,2-dimethyl-l-propoxy)titanium as a
titanium source in an organic solvent. For example, in the
formation of a BST thin film, the stock solution may further
contain a Sr compound and a Ba compound. Alternatively, a Sr
compound and a Ba compound may be used as two different
solutions.
[0046] When the different solutions are used, the organic solvents
may be the same or different. When one stock solution of all of the
raw compounds dissolved in an organic solvent is used, the
concentration of each compound in the solution is determined so
that a thin film having a predetermined composition is formed. The
titanate complex in accordance with the present invention has low
reactivity with the other raw compounds, for example, Sr(DPM).sub.2
and Ba(DPM).sub.2, for the dielectric thin film; hence the metallic
ratio in the dielectric thin film is substantially the same as the
metallic ratio in the raw compounds. As a result, the film
composition can be easily controlled.
[0047] Any organic solvents can be used without restriction in the
solution feeding method, and a preferred organic solvent is at
least one selected from the group consisting of cyclic or acyclic
alkanes, cyclic or acyclic monoethers and diethers, alkoxyalcohols,
diols, esters, and substituted or unsubstituted pyridines.
[0048] Since alkanes have low reactivity and low azeotropic vapor
pressure, Sr(DPM).sub.2 as an example can be dissolved as it is
into an alkane solvent without coordination of the solvent.
Accordingly, the solution can be steadily vaporized without
pyrolysis of the organometallic compounds before the compounds
reach the deposition chamber.
[0049] On the other hand, all of cyclic or acyclic monoethers and
diethers, alkoxyalcohols, diols, esters, and substituted or
unsubstituted pyridines are polar solvents. These polar solvent
other than esters coordinate with the organometallic compounds by
solvation to form complexes. Since esteric solvents have low
polarity and high viscosity, the dissolved organometallic compounds
are stable in the solution. Among these polar solvents,
tetrahydrofuran (THF), one of cyclic monoethers, has high
reactivity. Since the organic titanium compound in accordance with
the present invention is stable, it can be dissolved into THF
without deterioration of vaporization characteristics due to
reaction with the solvent.
[0050] It is preferable that cyclic or acyclic alkane solvents have
five to eight carbon atoms. Examples of the alkane solvents include
linear alkanes, e.g., n-pentane, n-heptane, and n-octane; branched
alkanes, e.g., isopentane and isooctane; and cycloalkanes, e.g.,
cyclopentane, cyclohexane, cycloheptane, and cyclooctane.
[0051] It is preferred that acyclic diethers be lower
dimethoxyalkanes and diethoxyalkanes having 3 to 12 carbon atoms
and more preferably no greater than 10 carbon atoms in view of the
boiling point. Examples of acyclic diethers include
dimethoxymethane, 1,1-dimethoxyethane, 1,2-dimethoxyethane,
1,1-diethoxyethane, 1,2-diethoxyethane,
3,4-dimethoxy-2,2-dimethylbutane, 3,4-dimethoxy-2,2-diethylbutane,
2,3-dimethoxy-1,1-dimethylpropane, 2,3dimethoxy-1,1-diethylpropane,
1,2-dimethoxyhexane, 1,2-diethoxyhexane, 1,2-dimethoxybutane,
1,2-diethoxybutane, 1,2-dimethoxypropane, and 1,2-diethoxypropane.
A preferable cyclic diether is dioxane.
[0052] The acyclic monoethers are generally dialkylethers, and the
two alkyl groups have preferably one to six carbon atoms. Although
monoethers having two linear alkyl groups (a typical example is
diethylether) can be used, monoethers having one or two branched
alkyl groups are preferable. Examples of such monoethers include
diisobutyl ether, diisopropyl ether, isobutyl methyl ether and
isobutyl ethyl ether.
[0053] Examples of cyclic monoethers include unsubstituted
tetrahydrofuran (THF), and lower-alkyl-substituted
tetrahydrofirans. Preferable examples of lower-alkylsubstituted
tetrahydrofuran include methyl- or dimethylsubstituted
tetrahydrofurans, such as, 2-methyltetrahydrofuran (2-methylTHF),
3-methyltetrahydrofuran (3-methylTHF), and
2,5-dimethyltetrahydrofuran (2,5dimethylTHF).
[0054] Alkoxyalcohols have preferably 3 to 12, and more preferably
no greater than 8 carbon atoms. Examples of such alkoxylalcohols
include 1-ethoxy-2-propanol and 1-butoxy-2-propanol.
[0055] Diols have preferably two to four carbon atoms. Propylene
glycol is more preferable.
[0056] Preferable esters are alkyl acetates and alkyl acetoacetates
wherein the alkyl has one to five carbon atoms. Examples of such
esters include methyl acetate, ethyl acetate, propyl acetate,
isopropyl acetate, butyl acetate, isobutyl acetate, pentyl acetate,
isopentyl acetate, methyl acetoacetate, and ethyl acetoacetate.
[0057] Among substituted or unsubstituted pyridines, pyridine and
lower-alkyl-substituted pyridines are preferable. Examples of the
lower-alkyl-substituted pyridines include 2,5-lutidine and
2,6-lutidine.
[0058] These solvents may be used alone or in combination. Examples
of more preferable solvents include methyl- or dimethyl-substituted
tetrahydrofurans, for example, 2-methylTHF, 3-methylTHF, and
2,5-dimethylTHF. A preferable mixed solvent is a combination of an
alkane (=acyclic saturated hydrocarbon) being a nonpolar solvent
with at least one polar solvent.
[0059] Although the stock solution can be directly evaporated from
the solution vessel, it is preferable that the solution be fed into
a heated vaporization chamber, instantaneously evaporated in the
vaporization chamber, and then the vapor be fed to the deposition
chamber. When different solutions of raw compounds are prepared, it
is preferable that these solutions be fed into a mixing chamber
provided in front of the vaporization chamber, and the solution
mixture be fed into the vaporization chamber. The stock solutions
may be fed by compressing them with an inert carrier gas, e.g.,
nitrogen, helium, or argon. The flow rate can be controlled by any
flow rate controller.
[0060] The concentration of the stock solution is not limited. In
the organic titanium compound in accordance with the present
invention, the concentration is preferably in a range of 0.05 M to
3.0 M, and more preferably 0.1 M to 2.0 M. Since the organic
titanium compound has high solubility, a highly concentrated
solution of 1 M or more can be prepared, and thus a significantly
high deposition rate can be achieved, as will be described
below.
[0061] Preferable film deposition conditions include a substrate
temperature in a range of 400 to 650.degree. C., and a deposition
pressure in a range of 5 to 20 Torr. The feeding rate of the stock
solution is preferably in a range of 0.05 to 0.5 cc/min. Use of a
carrier gas preferably performs the vaporization in either the
solid feeding method or the solution feeding method. Examples of
preferable carrier gases include inert gases, such as helium and
argon. The flow rate of the carrier gas is preferably in a range of
300 to 700 ccm. A reactive gas, for example, oxygen or an
oxygen-containing gas is supplied into the reaction chamber. The
feeding rate when oxygen is used is preferably in a range of 500 to
2,000 ccm. The deposition time is determined so that a dielectric
thin film having a predetermined thickness is formed. The
deposition time is generally shorter than that of conventional
processes, that is, less than one minute to several minutes. These
conditions may be outside the above-described ranges in some
cases.
[0062] The dielectric thin film produced by a MOCVD process using
an organic titanium compound in accordance with the present
invention is useful as a capacitor of a DRAM. When the organic
titanium compound in accordance with the present invention is used,
a dielectric thin film having superior step covering
characteristics can be produced for a short deposition time over a
wide temperature range and a wide range of concentration.
[0063] As shown in FIG. 1, when a thin film is deposited on a
substrate having an indented section with a volume of 1 .mu.m.sup.3
(that is, each of the length, width and depth is 1 .mu.m), the step
covering characteristics in the present invention is defined as the
ratio b/a of the film thickness b in the indented section to the
film thickness a on the flat portion of the substrate. A ratio near
to 1 means superior step covering characteristics. Thus, the ideal
b/a value is 1. In such a case, the thickness of the thin film is
preferably in a range of 15 to 30 mm.
[0064] As described above, the dielectric thin film formed of the
organic titanium compound in accordance with the present invention
is useful as a capacitor of a DRAM. The dielectric thin film also
can be used in piezoelectric vibrators and infrared sensors as
dielectric filters. Furthermore, the organic titanium compound in
accordance with the present invention can be used for the formation
of semiconductor films, optical thin films, surface-reinforcing
films, and thin-film catalysts.
[0065] Having generally described this invention, a further
understanding can be obtained by reference to certain specific
examples which are provided herein for purposes of illustration
only and are not intended to be limiting unless otherwise
specified.
EXAMPLE 1
[0066] Into 500 liters of benzene, 290 g (1 mol) of
tetraisopropoxytitanium was dissolved, 144 g (2 mol) of
2-methyl-l-propanol was added to the solution, and then the
solution was refluxed for 2 hours. The solution after the reaction
was cooled to room temperature, 368.5 g (2 mol) of
dipivaloylmethane was added, and then immediately the solution was
concentrated by heat. The solution was cooled, and the precipitated
crystal was separated by filtration. A powdered
bis(dipivaloylmethanato)-diisobutoxytitanium (150 g, the yield:
60%) was prepared. The melting point was 120 to 130.degree. C., and
the decomposition temperature was 300 to 340.degree. C.
[0067] The product was identified by .sup.1H-NMR, IR spectrometry,
mass spectrometry, and elemental analysis.
[0068] .sup.1H-NMR (C.sub.6D.sub.6+THF).delta.(ppm):
1.6[C(CH.sub.3).sub.3] 1.8(CH.sub.3), 3.4(CH.sub.2), 4.2(CH),
5.8(CH);
[0069] IR: 1,730, 1,725, 1,259, 1,300, 3,100, 1,330, 1,590, 1,600,
1,030, 670, 900, 110, 1,470;
[0070] Mass spectra (m/z): 31, 161, 342, 490, 538, 561;
[0071] Elemental analysis: C.sub.30H.sub.56O.sub.6Ti
[0072] (Calculated) C:64.22, H:10.06, 0:17.15, Ti:8.540
[0073] (Observed) C:64.25, H:10.07, 0:17.12, Ti:8.542
[0074] The mass spectrometric data shows that the organic titanium
compound in accordance with the present invention is present as a
monomer.
[0075] FIG. 2 is a TG-DTA thermogram of thermal gravimetry (TG) and
differential thermal analysis (DTA) of the compound at a heating
rate of 10.degree. C./min in an argon stream.
Example 2
[0076] White powdered
bis(dipivaloylmethanato)-di-(2,2-dimethyl-l-propoxy)- titanium
(yield: approximately 60%) was prepared as in Example 1, but 176 g
(2 mol) of 2,2-dimethyl-l-propanol was used instead of
2-methyl-l-propanol. Sublimed (180.degree. C./2 Torr),
decomposition temperature: 310 to 350.degree. C.
[0077] The product was identified by .sup.1H-NMR, IR spectrometry,
mass spectrometry, and elemental analysis.
[0078] .sup.1H-NMR (C.sub.6,D.sub.6+THF).delta.(ppm):
1.4[C(CH.sub.3).sub.3], 1.75(CH.sub.3), 3.4(CH.sub.2), 5.8(CH);
[0079] IR: 1,730, 1,725, 1,259, 1,300, 3,100, 3,150, 1,330, 1,590,
1,600, 1,030, 670, 110, 1,470;
[0080] Elemental analysis: C.sub.32H.sub.60O.sub.6Ti
[0081] (Calculated) C:65.1, H:10.1. 0:16.2, Ti:7.97
[0082] (Observed) C:64.9, H:10.4, 0:16.5, Ti:8.00
[0083] FIG. 3 is a TG-DTA thermogram of thermal gravimetry (TG) and
differential thermal analysis (DTA) of the compound at a heating
rate of 10.degree. C./min in an argon stream. The endothermic peak
due to melting is smaller than that of the compound in Example 1,
since the compound is sublimed.
[0084] FIG. 4 is a TG-DTA thermogram for comparison of thermal
gravimetry (TG) and differential thermal analysis (DTA) of
bis-(dipivaloylmethanato)- -diisopropoxytitanium, that is, a
conventional compound having an isopropyl group as an alkoxy group
instead of the isobutyl group.
[0085] By comparing FIGS. 2 and 3 (compounds in accordance with the
present invention) with FIG. 4 (a conventional compound),
bis(dipivaloylmethanato)-diisobutoxytitanium and
bis(dipivaloylmethanato)- -di-(2,2-dimethyl-l-propoxytitanium) in
accordance with the present invention have lower melting points
than that of known bis(dipivaloylmethanato)-diisopropoxytitanium.
Furthermore, thermal decomposition rapidly proceeds and the
decomposition is completed at approximately 280.degree. C. or less.
In contrast. the conventional compound is gradually decomposed, and
not completely decomposed at 350.degree. C. since the decomposition
is delayed at the final stage.
EXAMPLE 3
[0086] Using the organic titanium compound [Ti(DPM).sub.2
(O-i-Bu).sub.2] prepared in Example 1, the organic titanium
compound [Ti(DPM).sub.2(O-DMPr).sub.2] prepared in Example 2, and
the conventional isopropoxy compound [Ti(DPM).sub.2(O-i-Pr).sub.2]
as Ti sources, TiO.sub.2 thin films were formed by a solid feeding
method and a solution feeding method. An SiO.sub.2 substrate was
used. An indented portion with a width of 1 .mu.m, a length of 1
.mu.m, and a depth of 1 .mu.m ( 1 .mu.m.sup.3) had been formed on
the front surface of the substrate in order to evaluate step
covering characteristics.
[0087] The deposition conditions were as follows:
Solution Feeding Method
[0088] Solvent: THF
[0089] Substrate temperature: 450.degree. C.
[0090] Deposition time: 5 to 30 minutes
[0091] Deposition pressure: 10 Torr
[0092] Feeding rate of solution: 0.1 cc/min
[0093] Concentration of raw material: 0.1 to 2.0 M
[0094] Reactive gas: oxygen (1,000 ccm)
[0095] Vaporization temperature of raw material: 120.degree. C.
[0096] Carrier gas: helium (500 ccm)
Solid Feeding Method
[0097] Substrate temperature: 450.degree. C.
[0098] Deposition time: 5 to 30 minutes
[0099] Deposition pressure: 10 Torr
[0100] Concentration of raw material: 0.1 to 2.0 M
[0101] Reactive gas: oxygen (1,000 ccm)
[0102] Vaporization temperature of raw material: 120.degree. C.
[0103] Carrier gas: helium (500 ccm)
[0104] In the solution feeding method, these titanium compounds
were dissolved into THF to prepare three 0.1-M, 1.0-M and 2.0-M
stock solutions. Each of the stock solutions was fed into a
vaporization chamber heated to the vaporization temperature while
controlling feeding rate, and the resultant vapor was fed into a
deposition chamber with the carrier gas to form a TiO.sub.2 thin
film onto a substrate heated to the above-mentioned temperature in
the deposition chamber.
[0105] In the solid feeding method, each raw organic titanium
compound was vaporized at a vaporization temperature while flowing
the carrier gas, and the resultant vapor was fed into a deposition
chamber to form a TiO.sub.2 thin film onto a substrate heated to
the above-mentioned temperature in the deposition chamber.
[0106] The deposition time was changed from 5 minutes to 30 minutes
by 5 minutes. The thickness of the BST thin film formed on the
substrate was measured using a cross-sectional scanning electron
microscopic (SEM) photograph.
[0107] Using a solution having a low concentration of 0.05 M, a
thin film was deposited for a reduced deposition time, so that the
thickness was approximately 20 nm. The thicknesses of the TiO.sub.2
thin film at plural points in the indented section and the
periphery (the flat portion of the substrate) of the indented
section with a volume of 1 .mu.m.sup.3 were measured using a
cross-sectional SEM photograph and were averaged to determine the
thickness a of the periphery and the thickness b of the indented
section. The results of the ratio b/a as a measure of step covering
characteristics are shown in Table 1.
1TABLE 1 Concentration TiO.sub.2 film thickness at different
deposition Step Feeding of Solution time (nm) covering method (M) 5
min 10 min 15 min 20 min 25 min 30 min ratio (b/a) Titanium source:
Ti(DPM).sub.2 (O-i-Bu).sub.2 (this invention) Solid -- 150 300 500
600 700 800 .about.0.9 Solution 0.1 180 380 500 700 1,000 1,100
.about.0.9 1.0 1,500 2,800 4,500 5,800 7,200 8,800 .about.0.8 2.0
3,000 6,000 8,500 12,500 15,000 17,500 .about.0.9 Titanium source:
Ti(DPM).sub.2 (O-i-DMPr).sub.2 (this invention) Solid -- 135 250
400 550 680 800 .about.0.9 Solution 0.1 150 300 480 650 730 900
.about.0.9 1.0 1,200 2,800 3,400 4,500 6,100 7,100 .about.0.8 2.0
2,500 4,800 7,300 10,100 12,100 14,800 .about.0.9 Titanium source:
Ti(DPM).sub.2 (O-i-Pr).sub.2 (conventional) Solid -- 30 40 20 25 10
5 .about.0.2 Solution 0.1 50 100 70 60 20 10 .about.0.3 1.0 20 30
10 5 5 3 .about.0.2 2.0 5 15 38 20 8 1 .about.0.9
[0108] Table 1 shows that thin films can be formed at high
deposition rates by either the solid or liquid method in a MOCVD
process using bis(dipivaloylmethanato)diisobutoxytitanium or
bis(dipivaloylmethanato)-d- i-(2,2-dimethyl-l-propoxy)titanium in
accordance with the present invention as a Ti source. The
deposition rate by a solid feeding method is higher than that by a
solution feeding method. The thickness of the deposited film
increases substantially in proportion to the deposition time in
both solution and solid feeding methods. In the solution feeding
method, the thickness of the deposited film also increases
substantially in proportion to the concentration of the solution.
Thus, when the concentration of the solution in the solution
feeding method is increased by 2.0 m, the film thickness reaches
approximately 20 times or more that by the solid feeding method, or
the thickness is higher than 10,000 nm (10 .mu.m) for a deposition
time of 30 minutes.
[0109] Since the film thickness is substantially proportional to
the deposition time and the concentration of the solution in the
solution feeding method, the film thickness can be easily
controlled. Since the ratio showing step covering characteristics
is 0.8 or higher, and near to 1, a thin film having a substantially
uniform thickness can be deposited on the substrate having an
uneven surface.
[0110] When films were similarly deposited at a higher substrate
temperature of 600 to 650.degree. C., the thicknesses were
approximately 10 times those shown in Table 1, and the step
covering ratio was 0.8 or higher and the same level as that shown
in Table 1. Accordingly, superior step covering characteristics
were achieved at any temperature from a low temperature to a high
temperature.
[0111] In contrast, when known bis(dipivaloylmethanato)diisopropoxy
titanium was used as a Ti source, the film thickness was
significantly small at all deposition times compared to that of the
compounds in accordance with the present invention. Furthermore,
the thickness is not proportional to the deposition time or
concentration of the solution (in the solution feeding method). In
detail, the thickness reaches a maximum at 10 to 15 minutes, and
decreases at a longer deposition time. In the solution feeding
method, the thickness decreases as the concentration of the
solution increases, in contrast with the compounds in accordance
with the present invention.
[0112] For example, a large thickness of 10,000 nm or more is
achieved for a concentration of the solution of 2.0 M and a
deposition time of 30 minutes when using a compound in accordance
with the present invention, whereas a significantly small thickness
of 1 nm is achieved for the same-conditions using the conventional
compound.
[0113] Furthermore, the step-covering ratio is in a range of 0.1 to
0.3 and the thickness of the film formed in the indented section is
0.1 to 0.3 times that on the substrate surface.
[0114] The reason that the thickness is significantly small in the
conventional compound seems to be insufficient evaporation due to a
high vaporization temperature of the compound and low stability of
the vapor (high reactivity) causing polymerization. The reason that
the thickness decreases when the concentration of the solution is
high and when the deposition time is longer than a predetermined
time seems to be polymerization due to decreased molecular
stability under such conditions. Since the titanium compound in
accordance with the present invention has a low vaporization
temperature and high stability, hence it can be present as a
monomer. Furthermore, it has high stability in vapor, is rapidly
vaporized and, has high solubility, hence the film deposition rate
is high, and the film thickness increases substantially in
proportion to the deposition time and the concentration of the
solution.
[0115] When bis-(dipivaloylmethanato)-di-n-butoxytitanium is used
as another conventional compound instead of
bis(dipivaloylmethanato)-diisopr- opoxytitanium, similar results to
those of the conventional compound shown in Table 1 are
obtained.
EXAMPLE 4
[0116] TiO.sub.2 films were formed by a liquid feeding method as in
Example 3 using the organic titanium compound
[Ti(DPM).sub.2(O-i-Bu).sub.- 2] prepared in Example 1 in accordance
with the present invention or the organic titanium compound
[Ti(DPM).sub.2(O-DMPr).sub.2] prepared in Example 2 in accordance
with the present invention as a Ti source, and using
2,5-dimethyltetrahydrofuran (2,5-DMeTHF), 2-methyltetrahydrofuran
(2-MeTHF) or diisobutylether (DIBE) as a solvent in place of THF.
The results of the TiO.sub.2 film thickness and the step covering
ratio are shown in Table 2 for Ti(DPM).sub.2(O-i-Bu).sub.2 and
Table 3 for Ti(DPM).sub.2(O-DMPr).sub.2.
2TABLE 2 Titanium source: Ti(DPM).sub.2(O-i-Bu).sub- .2 (liquid
feeding method) Concentration TiO.sub.2 film thickness at different
deposition Step of solution time (nm) covering Solvent (M) 5 min 10
min 15 min 20 min 25 min 30 min ratio (b/a) 2,5-DMeTHF 0.1 200 400
510 680 980 1,200 .about.0.9 1.0 1,800 3,000 4,400 5,700 7,300
9,000 .about.0.9 2.0 2,900 5,800 8,800 12,550 14,900 18,000
.about.0.9 2-MeTHF 0.1 150 400 510 700 990 1,200 .about.0.9 1.0
1,510 3,000 4,800 6,000 7,300 9,000 .about.0.9 2.0 3,200 6,100
8,300 12,600 14,900 18,000 .about.0.9 DIBE 0.1 200 400 510 680
1,190 1,200 .about.0.9 1.0 1,800 3,000 4,800 6,100 7,300 9,000
.about.0.9 2.0 3,200 6,100 8,800 12,400 14,900 18,000 .about.0.9
2,5-DMeTHF = 2,5-dimethyltetrahydrofuran 2-MeTHF =
2-methyltetrahydrofuran DIBE = diisobutylether
[0117]
3TABLE 3 Titanium source: Ti(DPM).sub.2(O-DMPr).sub- .2 (liquid
feeding method) Concentration TiO.sub.2 film thickness at different
deposition Step of solution time (nm) covering Solvent (M) 5 min 10
min 15 min 20 min 25 min 30 min ratio (b/a) 2,5-DMeTHF 0.1 200 280
450 680 750 1,000 .about.0.9 1.0 1,100 3,000 3,500 4,800 6,200
7,000 .about.0.9 2.0 2,800 4,900 7,200 10,550 12,200 15,000
.about.0.9 2-MeTHF 0.1 200 340 480 680 730 920 .about.0.9 1.0 1,120
2,900 3,500 4,600 6,000 7,000 .about.0.9 2.0 2,510 4,900 7,200
10,120 12,200 15,000 .about.0.9 DIBE 0.1 180 320 500 660 750 1,010
.about.0.9 1.0 1,100 3,000 3,500 4,600 6,200 7,200 .about.0.9 2.0
2,800 4,900 7,300 10,110 12,120 15,000 .about.0.9 2,5-DMeTHF =
2,5-dimethyltetrahydrofuran 2-MeTHF = 2-methyltetrahydrofuran DIBE
= diisobutylether
[0118] The solvents other than THF shown in Tables 2 and 3 also
enables the rapid formation of TiO.sub.2 films by a liquid feeding
MOCVD process using the organic titanium compounds in accordance
with the present invention, wherein the thickness is substantially
proportional to the deposition time and the concentration of the
solution. The step-covering ratio is 0.9 or more which is higher
than that when THF is used as a solvent.
[0119] Substantially the same results were obtained when
3-methyltetrahydrofuran was used instead of 2-methyltetrahydrofuran
(2-MeTHF).
EXAMPLE 5
[0120] BST films were formed by a liquid feeding method using the
organic titanium compound [Ti(DPM).sub.2(O-i-Bu).sub.2] prepared in
Example 1 in accordance with the present invention or the organic
titanium compound [Ti(DPM).sub.2(O-DMPr).sub.2] prepared in Example
2 in accordance with the present invention as a Ti source.
Ba(DPM).sub.2 and Sr(DPM).sub.2 were used as a Ba source and a Sr
source, respectively.
[0121] These metal sources were dissolved in different solvents to
prepare stock solutions having concentrations of 0.1 to 0.2 M. The
stock solutions were fed into a mixing chamber while controlling
the flow rates so that the these metals satisfy the atomic ratio
Ba:Sr:Ti=0.5:0.5:1, and the solution mixture was vaporized in a
vaporization chamber. The vapor was fed into a deposition chamber,
and BST thin films were on a SiO.sub.2 substrates with Pt/It
electrodes formed thereon by sputtering (Pt/Ti/SiO.sub.2 substrate)
under the following conditions:
[0122] Substrate: Pt/Ti/SiO.sub.2
[0123] Substrate temperature: 400 to 650.degree. C.
[0124] Deposition pressure: 10 Torr
[0125] Feeding rate of solution: 0.05 cc/min
[0126] Concentration of raw material: 0.1 to 0.2 M
[0127] Reactive gas: oxygen (1,000 ccm)
[0128] Vaporization temperature of raw material: 200 to 250.degree.
C.
[0129] Carrier gas: helium (500 ccm)
[0130] Deposition time: 20 minutes
[0131] Experiments on film deposition were performed at different
substrate temperatures and using different solvents. The atomic
ratios of metals in the resulting thin films were determined by
fluorescent x-ray analysis. The results of the atomic ratio,
Ti/(Ba+Sr), are shown in Table 4 for Ti(DPM).sub.2(O-i-Bu).sub.2
and Table 5 for Ti(DPM).sub.2(O-DMPr).s- ub.2. Since the metal
source solutions were fed so as to satisfy the atomic ratio,
Ba:Sr:Ti=0.5:0.5:1, the resulting film should have a composition of
Ba.sub.05Sr.sub.05TiO.sub.3 and thus an atomic ratio of 1/1 in an
ideal state. For example, when the Ti/(Ba+Sr) atomic ratio is
0.1/0.3, this value means that the film contains large amounts of
inclusions such as carbon.
[0132] For comparison, BST films were also formed using known
TiO(DPM).sub.2 or TiO(DPM).sub.2(O-i-Pr).sub.2 as a titanium
source. The results are shown in Table 6.
4TABLE 4 Raw materials: Ba(DPM).sub.2 + Sr(DPM).sub.2 +
Ti(DPM).sub.2(O-i-Bu).sub.2 (Examples) Substrate Ti/(Ba + Sr)
temperature ratio in Solvent (.degree. C.) film THF 400 1.2/1.1 450
1.1/1.0 500 1.1/1.0 550 1.1/1.1 600 1.0/1.1 650 1.1/1.1 Pyridine
400 1.0/1.1 450 1.1/1.2 500 1.0/1.1 550 1.0/1.2 600 1.0/1.0 650
1.0/1.1 Isooctane 400 1.0/1.1 450 1.0/1.2 500 1.2/1.1 550 1.0/1.2
600 1.0/1.0 650 1.0/1.1 Octane 400 1.0/1.1 450 1.0/1.0 500 1.0/1.0
550 1.2/1.1 600 1.0/0.9 650 1.1/1.0 DMP 400 1.0/1.1 450 1.1/1.0 500
1.0/1.0 550 1.2/1.1 600 1.1/1.2 650 1.3/1.0 Lutidine 400 1.0/1.1
450 1.0/1.0 500 1.1/1.2 550 1.0/1.1 600 1.1/1.1 650 1.0/1.0 Butyl
400 1.0/1.1 acetate 450 1.1/1.1 500 1.0/1.0 550 1.1/1.0 600 1.0/1.1
650 1.0/1.1 Cyclo- 400 1.0/1.1 hexane 450 1.1/1.1 500 1.0/1.0 550
1.0/1.0 600 1.0/1.1 650 1.0/1.0 DMM 400 1.0/1.1 450 1.1/1.0 500
1.2/1.2 550 1.0/1.0 600 1.1/1.0 650 1.1/1.0 Hexane 400 1.0/1.1 450
1.0/1.0 500 1.1/1.2 550 1.0/1.1 600 1.1/1.1 650 1.2/1.0 Dioxane 400
1.0/1.0 450 1.0/1.0 500 1.1/1.2 550 1.1/1.0 600 1.2/1.1 650 1.1/1.0
Diisobutyl 400 1.0/1.0 ether 450 1.0/0.9 500 1.0/1.2 550 1.1/1.0
600 1.1/1.0 650 0.9/1.0 2MeTHF 400 1.0/1.1 450 1.0/1.0 500 1.1/1.1
550 1.0/1.1 600 1.1/1.0 650 1.0/1.0 Methyl 400 1.0/1.0 acetate 450
1.0/1.0 500 1.1/1.0 550 1.0/1.0 600 1.1/1.1 650 1.2/1.0 Isobutyl
400 0.9/0.9 acetate 450 1.0/1.0 500 1.0/1.0 550 1.0/1.1 600 1.1/1.1
650 1.0/1.0 Methyl 400 1.0/1.1 aceto- 450 1.1/1.1 acetate 500
1.0/1.0 550 1.0/1.0 600 1.0/1.1 650 1.0/1.0 2,5-DMeTHF 400 1.0/1.0
450 1.0/1.0 500 1.1/1.1 550 1.0/1.0 600 1.1/1.0 650 1.0/1.0 Ethyl
400 1.0/1.1 acetate 450 1.1/1.0 500 1.0/1.0 550 1.0/1.1 600 1.1/1.2
650 1.0/1.0 Pentyl 400 1.0/1.1 acetate 450 1.1/1.0 500 1.1/1.2 550
1.0/1.0 600 1.1/1.0 650 1.1/1.0 Ethyl 400 1.0/1.1 aceto- 450
1.0/1.2 acetate 500 1.1/1.1 550 1.0/0.9 600 1.0/1.0 650 1.0/1.0 1:1
400 1.0/1.1 mixture 450 1.1/1.0 of 500 1.1/1.0 2MeTHF 550 1.1/1.1
and 2,5- 600 1.0/1.0 DMeTHF 650 1.1/1.0 Isopropyl 400 1.0/1.1
acetate 450 1.1/1.0 500 1.0/1.1 550 1.0/1.2 600 1.0/1.0 650 1.0/1.1
Isopentyl 400 1.0/1.0 acetate 450 1.1/1.1 500 1.0/1.0 550 1.1/1.0
600 1.0/1.1 650 1.2/1.0 THF = tetrahydrofuran, DMP =
dimethoxypropane DMM = dimethoxymethane, 2MeTHF =
2-methyltetrahydrofuran 2,5-DMeTHF =
2,5-dimethyltetrahydrofuran
[0133]
5TABLE 5 Raw materials: Ba(DPM).sub.2 + Sr(DPM).sub.2 +
Ti(DPM).sub.2(O-DMPr).sub.2 (Examples) Substrate Ti/(Ba + Sr)
temperature ratio in Solvent (.degree. C.) film THF 400 1.0/1.0 450
1.1/1.1 500 1.0/1.1 550 1.2/1.0 600 1.1/1.2 650 1.0/1.0 Pyridine
400 1.0/1.0 450 1.1/1.1 500 1.0/1.1 550 1.0/1.2 600 1.0/1.0 650
1.0/1.1 Isooctane 400 0.9/0.9 450 1.0/1.2 500 1.0/1.0 550 1.0/1.0
600 1.0/1.0 650 0.9/0.8 Octane 400 1.0/1.0 450 1.0/1.1 500 1.0/1.0
550 1.0/1.1 600 1.1/1.2 650 1.0/1.0 DMP 400 1.1/1.0 450 1.0/1.1 500
1.1/1.0 550 1.0/1.0 600 1.1/1.2 650 1.1/1.0 Lutidine 400 1.0/1.0
450 0.9/0.9 500 1.1/1.2 550 0.9/1.0 600 1.1/1.1 650 1.1/1.0 Butyl
400 1.0/1.0 acetate 450 1.1/1.1 500 1.2/1.1 550 1.0/1.1 600 1.2/1.0
650 1.1/1.1 Cyclo- 400 1.0/1.0 hexane 450 1.1/1.1 500 1.1/1.1 550
1.0/1.0 600 1.2/1.1 650 1.1/1.0 DMM 400 1.1/1.0 450 1.0/1.1 500
1.2/1.1 550 1.1/1.0 600 1.2/1.2 650 1.2/1.2 Hexane 400 1.0/1.1 450
1.0/1.0 500 1.1/1.2 550 1.0/1.1 600 1.1/1.1 650 1.2/1.0 Dioxane 400
1.0/1.0 450 1.0/1.0 500 1.1/1.0 550 1.2/1.1 600 1.1/1.0 650 1.0/1.0
Diisobutyl 400 1.1/1.0 ether 450 1.0/1.0 500 1.1/1.1 550 1.2/1.1
600 1.1/1.0 650 1.0/1.0 2MeTHF 400 1.0/1.0 450 1.0/1.0 500 1.1/1.1
550 1.0/1.1 600 1.1/1.0 650 1.1/1.0 Methyl 400 1.0/1.1 acetate 450
1.0/1.0 500 1.1/1.0 550 1.0/1.1 600 1.1/1.1 650 1.2/1.0 Isobutyl
400 1.0/1.0 acetate 450 0.9/0.9 500 1.1/1.1 550 0.9/1.0 600 1.1/1.1
650 1.1/1.0 Methyl 400 1.0/0.9 aceto- 450 1.0/1.0 acetate 500
1.1/1.0 550 0.9/1.0 600 1.1/1.0 650 1.0/1.0 2,5-DMeTHF 400 1.0/1.0
450 1.0/1.1 500 1.2/1.1 550 1.1/1.0 600 1.2/1.1 650 1.1/1.2 Ethyl
400 1.1,1.0 acetate 450 1.0/1.0 500 1.1/1.0 550 1.0/1.0 600 1.1/1.1
650 1.1/1.0 Pentyl 400 0.9/1.0 acetate 450 1.1/1.0 500 1.1/1.1 550
1.1/1.0 600 1.2/1.0 650 1.2/1.2 Ethyl 400 0.9/1.0 aceto- 450
1.0/1.2 acetate 500 1.0/1.0 550 1.0/1.0 600 1.0/1.0 650 0.8/0.8 1:1
400 1.0/1.0 mixture 450 1.0/1.0 of 500 1.0/1.0 2MeTHF 550 1.1/1.0
and 2,5- 600 1.1/1.0 DMeTHF 650 1.0/1.0 Isopropyl 400 1.0/1.0
acetate 450 1.1/1.0 500 1.0/1.1 550 1.0/1.1 600 1.0/1.0 650 1.0/1.1
Isopentyl 400 1.0/0.9 acetate 450 1.1/1.1 500 1.2/1.1 550 1.0/1.1
600 1.1/1.0 650 1.1/1.0 THF = tetrahydrofuran, DMP =
dimethoxypropane DMM = dimethoxymethane, 2MeTHF =
2-methyltetrahydrofuran 2,5-DMeTHF =
2,5-dimethyltetrahydrofuran
[0134]
6TABLE 6 Substrate Ti/(Ba + Sr) temperature ratio in Solvent
(.degree. C.) film Raw materials: Ba(DPM).sub.2 + Sr(DPM).sub.2 +
TiO(DPM).sub.2 (Comparative Examples) THF 400 <0.1/0.1 450
<0.1/0.1 500 1.0/0.2 550 1.0/0.1 600 1.0/0.1 650 0.3/0.1 DMP 400
0.1/1.3 450 1.0/0.1 500 0.3/1.5 550 0.5/1.2 600 0.1/1.8 650 0.1/0.9
DMM 400 0.1/1.8 450 0.2/1.2 500 0.1/1.6 550 0.5/1.5 600 0.1/0.9 650
0.2/0.9 Raw materials: Ba(DPM).sub.2 + Sr(DPM).sub.2 +
Ti(DPM).sub.2(O-i-Pr).sub.2 (Comparative Examples) THF 400
<0.1/<0.1 450 <0.1/<0.1 500 0.5/0.1 550 0.8/0.1 600
0.8/0.1 650 0.5/0.2 DMP 400 <0.1/<0.1 450 <0.1/<0.1 500
<0.1/<0.1 550 0.2/<0.1 600 0.1/<0.1 650 0.2/<0.1 DMM
400 <0.1/<1.0 450 <0.1/<0.1 500 0.1/<0.1 550
0.3/<0.1 600 0.3/0.1 650 0.3/<0.1 THF = tetrahydrofuran, DMP
= dimethoxypropane, DMM = dimethoxymethane
[0135] As shown in Tables 4 and 5, when an organic titanium
compound in accordance with the present invention is used as a
titanium source, a BST thin film containing metals with a desired
atomic ratio (Ba/Sr=1/1, that is, Ba:Sr:Ti=1:1:2) can be formed at
various temperatures. Thus, the compound can effectively control
the composition of the film. The results illustrate that the
titanium complexes used in the present invention are stable in
solution and vapor and not reactive with Sr and B sources, hence
the stable compound is fed into a deposition chamber. The step
covering ratio b/a was measured as in Example 3, and was 0.8 or
more, that is, near 1 in all the solvents used. Thus, the compound
also has superior step covering characteristics.
[0136] In contrast, as shown in Table 6, when TiO(DPM).sub.2 is
used as a Ti source, the atomic ratio of the BST thin film
significantly deviates from that in the raw materials
[(Ba+Sr)/Ti=1/1]. Thus, the composition of the film is readily not
controlled. The step-covering ratio b/a was in a range of 0.1 to
0.3 and thus step covering characteristics are inferior. The film
deposition rate was significantly low.
[0137] The fine texture of the BST thin film formed using the
organic titanium compound in accordance with the present invention
was observed with an electron microscopic photograph. Crystal
grains were observed as granules in a photograph with a 1-.mu.m
scale when any solvents are used. The crystal grain size was
several tens of nm or less, and was significantly fine and uniform.
Examples of photographs when the organic titanium compounds in
accordance with the present invention are shown in FIG. 5 for
Ti(DPM).sub.2(O-i-Bu).sub.2 and FIG. 6 for
Ti(DPM).sub.2(O-DMPr).sub.2.
[0138] For comparison, the electron microscopic photographs of BST
thin films deposited using Ti(DPM).sub.2(O-i-Pr).sub.2 and
Ti(DPM).sub.2 as titanium sources are shown in FIG. 7(a) (scale: 3
.mu.m) and FIG. 7(b) (scale: 6 .mu.m), respectively. The BST thin
film shown in FIG. 7(a) using Ti(DPM).sub.2(O-i-Pr).sub.2 as a
titanium source has significantly coarser crystal grains compared
with the BST thin films using the titanium compounds in accordance
with the present invention, and has cracks. The BST thin film shown
in FIG. 7(b) using Ti(DPM).sub.2 as a titanium source has more
significantly coarser crystal grains and cracks. Such dielectric
thin films having coarse crystal grains and cracks do not show
desired characteristics, and reliability of the films is
significantly decreased.
EXAMPLE 6
[0139] BST films were formed using Ba(DPM).sub.2.multidot.TEG and
Sr(DPM).sub.2.multidot.TEG as a Ba source and a Sr source, as in
Example 5. That is, organic titanium compounds
Ti(DPM).sub.2(O-i-Bu).sub.2 of Example 1 and
Ti(DPM).sub.2(O-DMPr).sub.2 of Example 2 were used as Ti sources.
The analytical results of the compositions of the BST films are
shown in Table 7 for Ti(DPM).sub.2(O-i-Bu).sub.2 and Table 8 for
Ti(DPM).sub.2(O-DMPr).sub.2.
[0140] For comparison, BST films were similarly formed using known
TiO(DPM).sub.2 and TiO(DPM).sub.2(O-i-Pr).sub.2. The results are
shown in Table 9.
7TABLE 7 Raw materials: Ba(DPM).sub.2 .multidot. TEG +
Sr(DPM).sub.2 .multidot. TEG + Ti(DPM).sub.2(O-i-Bu).sub.2
(Examples) Substrate Ti/(Ba + Sr) temperature ratio in Solvent
(.degree. C.) film THF 400 1.1/1.0 450 1.0/1.0 500 1.1/1.2 550
1.1/1.0 600 1.1/1.2 650 1.1/1.1 Pyridine 400 1.0/1.1 450 1.2/1.1
500 1.2/1.1 550 1.0/1.2 600 1.0/1.0 650 1.0/1.1 Isooctane 400
1.0/1.1 450 1.0/1.1 500 1.0/1.1 550 1.0/1.2 600 1.0/1.0 650 1.0/1.1
Octane 400 1.0/1.0 450 1.0/1.0 500 1.0/1.0 550 1.1/1.1 600 1.0/1.1
650 1.0/1.0 DMP 400 1.0/1.0 450 1.0/1.0 500 1.1/1.1 550 1.1/1.2 600
1.0/1.1 650 1.0/1.1 Lutidine 400 1.0/1.1 450 1.0/1.0 500 1.1/1.0
550 0.9/1.0 600 0.8/1.0 650 0.9/1.0 Butyl 400 1.0/1.0 acetate 450
1.1/1.1 500 1.1/1.0 550 1.0/1.1 600 1.0/1.0 650 1.0/1.1 Cyclo- 400
1.0/1.0 hexane 450 1.1/1.1 500 1.0/1.0 550 1.0/1.1 600 1.0/1.0 650
1.0/1.0 DMM 400 1.1/1.0 450 1.1/1.1 500 1.1/1.2 550 1.1/1.0 600
1.0/1.1 650 1.1/1.2 Hexane 400 1.1/1.1 450 1.2/1.0 500 1.1/1.1 550
1.0/1.1 600 1.1/1.0 650 1.0/1.2 Dioxane 400 1.2/1.1 450 1.0/1.2 500
1.1/1.0 550 1.0/1.1 600 1.1/1.1 650 1.0/1.0 Diisobutyl 400 1.2/1.1
ether 450 1.0/1.0 500 1.1/1.0 550 1.0/1.1 600 1.1/1.1 650 1.0/1.0
2MeTHF 400 1.1/1.1 450 1.2/1.0 500 1.1/1.1 550 1.0/1.1 600 1.0/1.0
650 1.0/1.2 Methyl 400 1.1/1.1 acetate 450 1.2/1.0 500 1.1/1.1 550
1.0/1.1 600 1.1/1.0 650 1.0/1.0 Isobutyl 400 1.0/1.1 acetate 450
1.0/1.0 500 1.1/1.0 550 0.9/1.0 600 0.9/1.0 650 1.0/1.0 Methyl 400
1.0/1.1 aceto- 450 1.0/1.2 acetate 500 1.1/1.0 550 1.0/1.1 600
1.1/1.0 650 1.0/1.0 2,5-DMeTHF 400 1.0/1.0 450 0.9/1.0 500 1.1/1.2
550 0.9/1.0 600 1.0/1.1 650 1.1/1.1 Ethyl 400 1.0/1.0 acetate 450
1.0/1.0 500 1.1/1.0 550 1.1/1.2 600 1.0/1.1 650 1.0/1.1 Pentyl 400
1.1/1.0 acetate 450 1.1/1.1 500 1.1/1.0 550 1.1/1.0 600 1.0/1.1 650
1.1/1.1 Ethyl 400 1.0/1.0 aceto- 450 1.0/1.1 acetate 500 1.0/1.1
550 1.0/0.9 600 1.0/1.0 650 1.0/1.1 1:1 400 1.0/1.0 mixture 450
1.0/1.0 of 500 1.1/1.2 2MeTHF 550 1.1/1.0 and 2,5- 600 1.1/1.1
DMeTHF 650 1.1/1.1 Isopropyl 400 1.0/1.0 acetate 450 1.2/1.1 500
1.2/1.1 550 1.0/1.1 600 1.0/1.0 650 1.0/1.0 Isopentyl 400 1.0/1.0
acetate 450 0.9/1.1 500 1.1/1.0 550 1.0/1.0 600 1.0/1.0 650 1.1/0.9
THF = tetrahydrofuran, DMP = dimethoxypropane DMM =
dimethoxymethane, 2MeTHF = 2-methyltetrahydrofuran 2,5-DMeTHF =
2,5-dimethyltetrahydrofuran
[0141]
8TABLE 8 Raw materials: Ba(DPM).sub.2 .multidot. TEG +
Sr(DPM).sub.2 .multidot. TEG + Ti(DPM).sub.2 (Examples) Substrate
Ti/(Ba + Sr) temperature ratio in Solvent (.degree. C.) film THF
400 1.1/1.0 450 1.0/1.1 500 1.1/1.1 550 1.2/1.1 600 1.1/1.0 650
1.0/1.1 Pyridine 400 1.0/1.0 450 1.2/1.1 500 1.2/1.1 550 1.1/1.0
600 1.0/1.0 650 1.0/1.0 Isooctane 400 1.0/1.1 450 1.0/1.1 500
1.0/1.0 550 1.1/1.0 600 1.0/1.0 650 1.0/1.1 Octane 400 1.0/1.1 450
1.0/1.0 500 1.0/1.0 550 1.1/1.1 600 1.1/1.0 650 1.1/1.1 DMP 400
1.1/1.1 450 1.0/1.0 500 1.0/1.0 550 1.1/1.2 600 1.1/1.0 650 1.1/1.1
Lutidine 400 1.0/1.1 450 1.0/1.0 500 1.1/1.1 550 0.9/1.0 600
0.9/0.9 650 0.9/0.8 Butyl 400 1.0/1.1 acetate 450 1.1/1.1 500
1.0/1.0 550 1.1/1.0 600 1.0/1.0 650 1.1/1.0 Cyclo- 400 1.0/1.1
hexane 450 0.9/1.0 500 1.0/1.0 550 1.0/1.0 600 1.0/1.0 650 1.1/1.0
DMM 400 1.0/1.0 450 1.1/1.0 500 1.0/1.0 550 1.1/1.1 600 1.0/1.1 650
1.2/1.0 Hexane 400 1.1/1.1 450 1.1/1.1 500 1.1/1.1 550 1.0/1.1 600
1.0/0.9 650 1.0/1.2 Dioxane 400 1.1/1.1 450 1.0/1.0 500 1.1/1.1 550
1.0/1.2 600 1.1/1.2 650 1.1/1.1 Diisobutyl 400 1.1/1.1 ether 450
1.0/1.0 500 1.0/1.1 550 1.0/1.2 600 1.1/1.1 650 1.1/1.1 2MeTHF 400
1.1/1.1 450 1.1/1.0 500 0.9/1.0 550 1.0/1.1 600 1.0/0.9 650 1.0/1.2
Methyl 400 1.1/1.1 acetate 450 1.1/1.0 500 1.1/1.1 550 1.0/1.1 600
1.0/0.9 650 1.0/1.2 Isobutyl 400 1.0/1.0 acetate 450 1.0/1.0 500
1.1/1.1 550 0.9/1.0 600 0.9/0.9 650 0.9/0.8 Methyl 400 1.1/1.0
aceto- 450 1.0/1.0 acetate 500 1.1/1.1 550 1.0/1.2 600 1.0/1.1 650
1.1/1.1 2,5-DMeTHF 400 1.0/1.0 450 1.0/0.9 500 1.0/1.0 550 1.1/1.0
600 1.0/1.1 650 1.0/1.0 Ethyl 400 1.1/1.0 acetate 450 1.0/1.0 500
1.0/1.0 550 1.1/1.1 600 1.1/1.0 650 1.1/1.1 Pentyl 400 0.9/1.0
acetate 450 1.1/1.0 500 0.9/1.0 550 1.1/1.1 600 1.0/1.1 650 1.1/1.0
Ethyl 400 1.0/0.9 aceto- 450 1.0/1.1 acetate 500 1.1/1.0 550
1.1/1.0 600 1.0/1.0 650 1.0/0.9 1:1 400 1.0/1.0 mixture 450 1.0/1.1
of 500 1.1/1.1 2MeTHF 550 1.2/1.0 and 2,5- 600 1.1/1.0 DMeTHF 650
1.0/1.1 Isopropyl 400 1.0/1.0 acetate 450 1.2/1.1 500 1.2/1.1 550
1.0/1.0 600 1.0/1.0 650 1.0/0.9 Isopentyl 400 1.0/1.1 acetate 450
1.1/1.1 500 1.0/1.0 550 1.0/1.0 600 1.0/1.0 650 1.1/1.0 THF =
tetrahydrofuran, DMP = dimethoxypropane DMM = dimethoxymethane,
2MeTHF = 2-methyltetrahydrofuran 2,5-DMeTHF =
2,5-dimethyltetrahydrofuran
[0142]
9 TABLE 9 Substrate Ti/(Ba + Sr) temperature ratio in Solvent
(.degree. C.) film Raw materials: Ba(DPM).sub.2 .multidot. TEG +
Sr(DPM).sub.2 .multidot. TEG + TiO(DPM).sub.2 (Comparative
Examples) THF 400 1.2/<0.1 450 1.5/0.1 500 1.0/0.3 550
1.4/<0.1 600 1.3/<0.1 650 1.0/<0.1 DMP 400 0.1/1.3 450
0.1/1.0 500 0.2/1.2 550 0.1/1.0 600 0.3/1.8 650 0.4/1.5 DMM 400
0.1/1.5 450 0.1/1.2 500 0.2/1.0 550 0.4/1.0 600 0.1/1.5 650 0.2/1.8
Raw materials: Ba(DPM).sub.2 .multidot. TEG + Sr(DPM).sub.2
.multidot. TEG + Ti(DPM).sub.2(O-i-Pr).sub- .2 (Comparative
Examples) THF 400 1.8/<0.1 450 1.0/<0.1 500 0.7/<0.1 550
0.7/<0.1 600 0.9/<0.1 650 0.6/0.1 DMP 400 0.1/1.8 450 0.1/1.6
500 0.3/1.2 550 0.9/0.1 600 0.3/1.5 650 0.2/1.6 DMM 400 1.2/0.1 450
1.0/0.3 500 0.9/0.1 550 1.2/0.5 600 1.6/0.4 650 1.8/0.2 THF =
tetrahydrofuran, DMP = dimethoxypropane, DMM = dimethoxymethane
[0143] As shown in Tables 7 to 9, results of film deposition
similar to those in Example 5 are obtained when the Ba and Sr
sources are replaced. That is, when Ti(DPM).sub.2(O-i-Bu).sub.2 or
Ti(DPM).sub.2(O-DMPr).sub.2 in accordance with the present
invention is used as a Ti source, a BST thin film having a
composition near the atomic ratio of the raw materials is formed.
Thus, the film can control the composition. The step covering
characteristics and the thickness were similar to those in Example
5.
[0144] In contrast, the conventional titanium complex as a titanium
source causes a large fluctuation in the film thickness. Thus, the
thickness cannot be controlled.
[0145] The advantage of the present invention is that a novel
titanium complex in accordance with the present invention has a low
vaporization temperature, is stable in solution and vapor, and is
rapidly decomposed at lower than 280.degree. C.; hence it is
suitable for a titanium source in the production of a dielectric
thin film by a MOCVD process. When the titanium complex in
accordance with the present invention is used, a dielectric thin
film having a thickness which is substantially proportional to the
deposition time and the concentration of the raw materials in the
solution; hence the thickness can be readily and precisely
controlled and the deposition rate can be significantly increased
compared to conventional processes. A dielectric thin film allowing
readily controlling the film composition and having superior step
covering characteristics can be formed over a significantly wide
temperature range from a low temperature to a high temperature.
Accordingly, the present invention contributes to both improvements
in characteristics of BST and other dielectric thin films and
effective formation of thin films.
[0146] The disclosure of Japanese priority applications Hei
10-027241, filed Feb. 9, 1998; Hei 10-027243, filed Feb. 9, 1998;
and Hei 10-059581, filed Mar. 11, 1998, are hereby incorporated by
reference.
[0147] Obviously, numerous modifications and variations of the
present invention are possible in light of the above teachings. It
is therefore to be understood that within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described herein.
* * * * *