Metalorganic chemical vapor deposition of antimony oxide films on semiconductor substrates

Article abstract of DOI:10.1023/A:1015861418396

The growth kinetics of oxide films on silicon and gallium arsenide substrates were studied, using alkyl and alkoxide metalorganic precursors (triethylantimony, tripropylantimony, antimony butoxide, and antimony tri-β-aminoethoxide). The effect of thermal annealing on the microstructure and properties of the films was examined. Analysis of the deposition kinetics, composition, and properties of the films demonstrates that metalorganic chemical vapor deposition in an oxidizing atmosphere, using antimony butoxide or triethylantimony as a precursor, enables the growth of insulating layers on Si and GaAs at low temperatures (130-300°C).

Full text of DOI:10.1023/A:1015861418396

Inorganic Materials, Vol. 38, No. 6, 2002, pp. 576–581. Translated from Neorganicheskie Materialy, Vol. 38, No. 6, 2002, pp. 700–705.
Original Russian Text Copyright © 2002 by Mittov, Ponomareva, Mittova.
Metalorganic Chemical Vapor Deposition
of Antimony Oxide Films on Semiconductor Substrates
†
O. N. Mittov , N. I. Ponomareva, and I. Ya. Mittova
Voronezh State University, Universitetskaya pl. 1, Voronezh, 394693 Russia
e-mail: xelga@mailru.com
Received October 29, 2001
Abstract—The growth kinetics of oxide films on silicon and gallium arsenide substrates were studied, using
alkyl and alkoxide metalorganic precursors (triethylantimony, tripropylantimony, antimony butoxide, and anti-
mony tri-β-aminoethoxide). The effect of thermal annealing on the microstructure and properties of the films
was examined. Analysis of the deposition kinetics, composition, and properties of the films demonstrates that
metalorganic chemical vapor deposition in an oxidizing atmosphere, using antimony butoxide or triethylanti-
mony as a precursor, enables the growth of insulating layers on Si and GaAs at low temperatures (130–300°C).
INTRODUCTION
the range of alkoxides suitable for producing oxide lay-
ers, since these precursors are safe to handle and allow
one to deposit oxide films without introducing oxygen
into the reactor.
The objective of this work was to grow antimony
oxide films on semiconductor substrates by MOCVD
using alkyl (triethylantimony and tripropylantimony)
and alkoxide (antimony butoxide and antimony tri-β-
aminoethoxide) precursors and to examine the effect of
subsequent annealing on the composition, structure,
and properties of the films.
Metalorganic chemical vapor deposition (MOCVD)
plays an important role in the fabrication of semicon-
ductor devices and integrated circuits on III–V sub-
strates because these may decompose at relatively low
temperatures. The low structural perfection of thermal
oxide layers on gallium arsenide stimulates a search for
low-temperature methods of growing oxide films on
this material. During the growth of thermal oxide on
GaAs, only a small amount of arsenic is incorporated
into the film; the major portion of the arsenic accu-
mulates at the film–substrate interface [1]. If the vapor
phase contains MO compounds of Group V elements
EXPERIMENTAL
(
e.g., Sb and Bi), these may substitute for arsenic in the
GaAs substrate, and subsequent oxidation of such
The boiling points and refractive indices of the MO
structures will notably improve the quality of the oxide precursors synthesized by the procedures described
film.
below differed very little from those reported earlier
10]. All of the starting chemicals used were of reagent
grade.
[
In earlier studies, to produce aluminum, gallium,
and indium oxide films by MOCVD, use was made of
metal alkyl and alkoxide precursors [2]. There are,
however, no reports dealing with the deposition of anti-
mony oxide films. Powell et al. [3] and Anokhin et al.
Tripropylantimony was synthesized by reacting
SbCl with propylmagnesium bromide in flowing inert
3
gas:
[
4] deposited alumina and indium oxide films via pyrol-
ysis of trialkyl compounds. For other metal oxides,
SbCl + 3C H MgBr = Sb(C H ) + 3MgBrCl.
3
3
7
3
7 3
alkyl compounds were not used because they are First, propylmagnesium bromide was prepared by
extremely reactive with air and moisture. A safer proce- reacting magnesium with propyl bromide. To this end,
dure for depositing gallium oxide films was proposed magnesium filings (12 g) were placed in a solution of
by Vishnyakov et al. [5], who used a solution of trime- propyl bromide (45 ml) in diethyl ether (150 ml). The
thylgallium in diethyl ether. Since alkyls contain no resultant propylmagnesium bromide was then intro-
oxygen, the process must be run in an oxidizing atmo- duced into a three-neck flask fitted with a stirrer, reflux
sphere. This is not necessary with metal alkoxides, condenser with a CaCl -filled jacket, dropping funnel,
2
which are often used as precursors for MOCVD of and inlet for inert gas. After the flask was cooled to 0°C,
oxide films. In particular, alumina films were deposited a solution of SbCl (38 g) in diethyl ether (150 ml) was
3
in a number of studies [5–9] using aluminum isopro- added with stirring. The mixture was boiled for 30 min
poxide. Note that it is of considerable interest to extend and then, after cooling to 0°C, transferred to a separa-
tory funnel. After removing the uppermost layer, it was
vacuum-distilled to give tripropylantimony.
†
Deceased.
0
020-1685/02/3806-0576$27.00 © 2002 MAIK “Nauka/Interperiodica”

METALORGANIC CHEMICAL VAPOR DEPOSITION OF ANTIMONY OXIDE FILMS
577
Triethylantimony was synthesized in a similar way, annealing on the film microstructure and properties, the
by reacting SbCl with ethylmagnesium bromide in films deposited in an argon atmosphere were then
3
flowing inert gas.
Antimony butoxide was prepared by reacting SbCl3
with butyl alcohol in the presence of ammonia:
annealed for 30 min at 300, 350, and 400°C in oxygen,
a mixture of oxygen and water vapor, or argon.
Film thicknesses were measured with an E-3 ellip-
someter to an accuracy of ±1 nm. Film composition was
determined by IR spectroscopy (UR-20 instrument),
electron diffraction (EG-100A unit), and electron probe
x-ray microanalysis (Camscan SI scanning electron
microscope equipped with a Link AN10/55 energy-dis-
persive x-ray analysis system). The surface morphol-
ogy of the films was examined using an MII-4 interfer-
ence microscope and ARM-1000 electron microscope.
SbCl + 3C H OH + 3NH = Sb(OC H ) + 3NH Cl.
3
4
9
3
4
9 3
4
To this end, SbCl (228 g) and absolute butyl alcohol
3
(
550 ml) were mixed in a three-neck flask fitted with a
stirrer, condenser, and an inlet tube for ammonia. After
cooling to 0°C, ammonia was bubbled through the mix-
ture. The precipitating ammonium chloride was then
collected on a filter. The filtrate was vacuum-distilled to
separate antimony butoxide.
Antimony tri-β-aminoethoxide was prepared via
transesterification of antimony butoxide with ethyl Cel-
losolve and ethanolamine:
RESULTS AND DISCUSSION
Our results on the kinetics of film deposition via
thermal decomposition of triethylantimony are summa-
rized in Table 1 and Fig. 1. The film thickness was
found to vary linearly with deposition time. Prelimi-
nary experiments showed that the deposition rate
(
n-C H O) Sb + NH C H OH
4 9 3 2 2 4
=
(NH C H O) Sb + n-C H OH.
2 2 4 3 4 9
Antimony butoxide (5 g) and a small excess of ethano- depended strongly on whether the solution was used as-
lamine were introduced into a vacuum-distillation prepared or after storage. The nature of the substrate
flask. After distilling off the butyl alcohol, the resultant had no significant effect on the deposition rate, which is,
antimony tri-β-aminoethoxide was vacuum distilled.
in addition, almost temperature-independent (Table 1).
This may be due to the fact that the MO precursor fully
decomposes even at 130°C, and the deposition rate is
then controlled by the flow rate of the carrier gas [1]. In
the case of the pyrolysis of a triethylantimony solution
in toluene, the growth rate even decreases with increas-
ing temperature. Increasing the triethylantimony con-
centration in butyl alcohol slightly increases the depo-
sition rate (Fig. 1). The rate constants for the pyrolysis
of solutions with Sb(C H ) : C H OH = 1 : 1 and 2 : 1
The substrates used in kinetic studies were polished
wafers of AGP-1 and AGChTs GaAs(100) with a car-
1
6
–3
rier concentration of 10 cm and KEF Si with an elec-
trical resistivity of 7.5 Ω cm. The process was run in a
resistance-heated two-zone furnace. The temperature
was maintained with a stability of ±1°C. The source and
deposition temperatures were chosen using thermo-
gravimetric data (Paulik–Paulik–Erdey system).
2
5 3
4
9
We used single- and two-zone procedures. In the
former case, the MO precursor (antimony butoxide,
tripropylantimony, or antimony tri-β-aminoethoxide)
was placed in a quartz container, which was then cov-
ered with the substrate. In the two-zone procedure, the
container with the precursor (triethylantimony) was sit-
uated in the lower temperature zone, where the precur-
sor vaporized without decomposition, and the substrate
was located in the higher temperature zone, where the
precursor decomposed.
differ insignificantly: 6 ± 0.4 and 7 ± 0.8 nm/min.
Interestingly enough, the refractive index of the
films is essentially independent of the nature of the sol-
vent and substrate and increases with deposition tem-
perature, pointing to changes in film composition
(Table 1). The refractive index varies from 1.67 to 2.06,
3
00
250
00
150
Given that antimony alkyl compounds are unstable
in air and extremely reactive, we used their solutions in
butyl alcohol or toluene. In the case of triethylanti-
4
3
2
mony, we employed solutions with Sb(C H )
:
2
5 3
C H OH = 1 : 1 or 2 : 1 and Sb(C H ) : C H CH = 1 : 1
2
1
4
9
2
5 3
6
5
3
1
00
50
by volume. The solution temperature was 90°C, and the
substrate (Si or GaAs) temperature was 130, 190, or
3
00°C. This range of deposition temperatures was cho-
sen because, below 130°C, no film growth occurred,
while, above 300°C, the deposition rate was too high,
resulting in poor bonding between the film and the sub-
strate. The flow rate of argon carrier gas was 18 l/h in
all deposition runs.
0
5
10
15
20
25
30
35
40
Deposition time, min
Fig. 1. Film thickness as a function of deposition time for
films deposited on GaAs via triethylantimony pyrolysis at
(
1, 3, 4) 190 and (2) 130°C and an Sb(C H ) : C H OH
2 5 3 4 9
The etching behavior of the films was studied using
.2% hydrochloric acid. To study the effect of thermal
ratio of (1–3) 1 : 1 and (4) 2 : 1; (1, 2) 30 min after solution
preparation, (3, 4) freshly prepared solution.
7
INORGANIC MATERIALS Vol. 38 No. 6 2002

5
78
MITTOV et al.
1
1
20
00
8
6
4
2
0
0
0
0
3
5
8
1
2
6
4
7
0
200 400 600 800 1000 1200 1400 1600 1800 2000
Etching time, min
Fig. 2. Film thickness as a function of etching time in 7.2% hydrochloric acid for films deposited on (1–6, 8) GaAs and (7) Si at
(
1, 3) 130, (2, 5, 7, 8) 190, and (4, 6) 300°C via triethylantimony pyrolysis at (1, 2) Sb(C H5)3 : C H CH = 1 : 1,
2 6 5 3
(
3−7) Sb(C H ) : C H OH = 1 : 1, and (8) Sb(C H ) : C H OH = 2 : 1; (4) oxygen annealing at 300°C for 20 min.
2
5 3
4
9
2
5 3
4 9
which corresponds to different Sb O polymorphs [11]. rate also depends on the initial triethylantimony con-
2
4
According to x-ray microanalysis data, the films on centration: at higher concentration, the etching rate is
GaAs consist of Sb and O, and those on Si contain, in slower. The etching behaviors of the films deposited on
addition, carbon. The IR spectra of the films show an
absorption band at 820 cm , due to the Sb–O bond [12].
Si and GaAs are similar. The only difference is that the
backside of the films grown on GaAs dissolves more
rapidly, which is attributable to the diffusion of Ga and
As into the film. With increasing deposition tempera-
ture, the etching rate of the frontside decreases; the
-1
The backside and frontside of the films were found
to differ in etching rate (Fig. 2). Moreover, the etching
rate of the films produced using triethylantimony solu-
tions in toluene is much faster than that of the films same is observed after annealing. MOCVD films typi-
deposited from solutions in butyl alcohol. The etching cally contain residual organics and trace amounts of
Table 1. Properties of the films deposited on GaAs and Si using triethylantimony
Solution
t, °C
Substrate
τ, min
d, nm
n
v, nm/min
Sb(C H ) : C H OH = 1 : 1
130
AGP GaAs
15–40
64–113
1.67–1.73
3–4
2
5 3
4
9
(
after 30-min storage)
1
3
90
00
AGP GaAs
AGP GaAs
AGP GaAs
15–50
30
54–113
84
1.75–1.95
2.03
2–4
3
Sb(C H ) : C H OH = 1 : 1
190
190
11–25
40–122
1.68–1.86
4–5
2
5 3
4
9
(
as-prepared)
Sb(C H ) : C H OH = 2 : 1
AGP GaAs
8–30
39–191
1.76–2.68
5–6
2
5 3
4
9
(
as-prepared)
1
90
KEF Si
10–20
15–30
53–92
1.76–1.78
1.65–2.18
5
Sb(C H ) : C H CH = 1 : 1
130
AGP GaAs
109–294
6–10
2
5 3
6
5
3
(
as-prepared)
1
1
3
3
90
90
00
00
AGP GaAs
KEF Si
15
15
30
30
116
102
108
94
1.69
1.72
2.03
1.98
8
7
4
3
AGChTs GaAs
KEF Si
INORGANIC MATERIALS Vol. 38 No. 6 2002

METALORGANIC CHEMICAL VAPOR DEPOSITION OF ANTIMONY OXIDE FILMS
579
Table 2. Effect of annealing in argon atmosphere on the thickness and refractive index of films deposited on GaAs using a
1
: 1 solution of Sb(C H ) in C H OH
2
5 3
4
9
d, nm
n
d, nm
n
tpyr, °C
tann, °C
Gas phase
τann, min
before annealing
after annealing
130
130
130
190
190
190
190
300
300
300
300
300
400
400
400
400
400
400
400
350
350
350
350
400
O2
20
30
20
20
30
20
20
20
20
20
20
20
78
95
1.69
36
34
46
81
74
75
85
94
82
87
88
73
1.88
1.84
1.85
1.90
1.83
1.86
1.78
2.05
2.03
2.0
O2
1.67
1.67
1.81
1.81
1,81
1.81
2.0
H O(g) + O
95
2
2
O2
O2
108
108
108
108
90
H O(g) + O
2
2
H O(g) + O
2
2
O2
O2
84
2.03
2.0
H O(g) + O
90
2
2
Ar
Ar
90
2.0
2.01
2.02
84
2.03
water [1], which are removed in the course of thermal
We failed to produce antimony oxide films by
annealing, which, accordingly, raises the film density MOCVD in oxygen or air using tripropylantimony.
and improves the film–substrate adhesion.
Only in a mixture of H O and O were deposition runs
2 2
successful. The thickness of the film deposited in 2 min
was 200 nm. Deposition kinetics of such films were not
studied because tripropylantimony is difficult to syn-
thesize.
Table 2 lists the thicknesses and refractive indices of
the films before and after annealing in different atmo-
spheres. Both in oxygen and water vapor, annealing
reduces the thickness and increases the refractive index
of the films deposited at 130 and 190°C, while those of
the films grown at 300°C remain virtually unchanged.
Table 3. Effect of annealing on the composition of films de-
posited via triethylantimony pyrolysis (x-ray microanalysis
Annealing was found to have different effects on the on a Camscan SI scanning electron microscope equipped
microstructure of the films deposited at high and low with a Link AN10/55 energy-dispersive x-ray analysis sys-
tem)
temperatures. The films deposited at 300°C and
annealed at 400°C were nonuniform in thickness: in
some regions, the film thickness was larger than that
before annealing. This effect seems to be due to further
oxidation of the partially oxidized antimony during
annealing. At annealing temperatures below 400°C,
this effect was not detected. The films grown at 130 and
Atomic percent
Sub- Deposition/annealing
Analyte
strate
temperature
Sb
O
C
GaAs 190°C
Film
Film
62
60
38
40
–
–
1
90°C were uniform in thickness after annealing at any
190°C, annealing
at 400°C
temperature. The compositions of the films before and
after annealing, as determined by x-ray microanalysis,
are listed in Table 3.
Same as above
Island
Film
57
56
54
43
44
46
–
–
–
3
00°C
The electric strength of the films grown on GaAs
and Si using triethylantimony rises with deposition
temperature and is higher when toluene is used as the
solvent (Table 4). The nature of the substrate has an
insignificant effect on the electrical properties of the
films.
300°C, annealing
at 400°C
Island
Si
190°C, annealing
at 400°C
Island
45
43
12
INORGANIC MATERIALS Vol. 38 No. 6 2002

5
80
MITTOV et al.
Table 4. Electric strength and refractive indices of films deposited via triethylantimony pyrolysis
–5
MO precursor
Substrate
t, °C
d, nm
n
E × 10 , V/cm
br
Sb(C H ) : C H OH = 1 : 1
AGChTs GaAs(100)
AGChTs GaAs(100)
KEF Si(111)
190
190
190
300
300
300
90
108
75
1.72
1.84
1.75
2.01
2.03
1.98
3
2
5 3
4
9
1.4
37
AGChTs GaAs(100)
AGChTs GaAs(100)
KEF Si(111)
95
5.3
9.3
8.5
Sb(C H ) : C H CH = 1 : 1
108
94
2
5 3
6
5
3
Alkoxide precursors offer a number of advantages ent activation energy of the deposition process, deter-
over alkyls: they are cheaper, much more stable in air, mined from the Arrhenius plot for K (Fig. 3b) [13], is
av
and safer in handling. In our preparations, insulating 22 kJ/mol. According to x-ray diffraction data, the films
layers were for the first time grown on GaAs by deposited with the use of antimony butoxide consist of
MOCVD using antimony butoxide and antimony tri-β- Sb O and are polycrystalline. The films adhere tena-
2
3
aminoethoxide.
ciously to the substrate and have a dielectric strength in
the range 8 × 10 to 3 × 10 V/cm.
Thermal decomposition of tri-β-aminoethoxide in
oxygen yielded oxide films even at 200°C, with a dep-
osition rate of 200 nm/min. The grown films loosely
adhered to the substrate and were unstable during air
storage.
5
6
The log–log plots of film thickness vs. deposition
time for the antimony butoxide precursor yield straight
lines (Fig. 3a), indicating power-law behavior, d = K τ
n n
[
13]. The exponent n is 3.00, 2.94, and 1.75 for the pro-
cesses at 150, 170, and 190°C, respectively. The appar-
logd [nm]
8
CONCLUSION
3
Our results demonstrate that MOCVD with the use
of triethylantimony in an oxidizing atmosphere is an
attractive process for producing insulating layers on sil-
icon and gallium arsenide at low temperatures (130–
(
a)
2
7
6
5
4
1
3
00°C). The main drawback to this precursor—its
instability even at room temperature—can be obviated
by using its solutions in toluene or butyl alcohol. The
resulting layers consist mainly of pyrolytic antimony
oxide and contain a minor amount of carbon.
The use of antimony butoxide as an MO precursor
makes it possible to deposit Sb O films at low temper-
atures. As distinct from triethylantimony, this precursor
does not require the presence of oxidants in the gas
phase and, owing to its stability, facilitates the deposi-
tion process.
2
3
–
1.0
–0.5
0
0.5
b)
1.0
lnτ [min]
0
.8
.7
.6
.5
.4
.3
.2
.1
(
0
0
0
0
0
0
0
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2
3
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