APPLIED PHYSICS LETTERS
VOLUME 72, NUMBER 14
6 APRIL 1998
Optical and electrical properties of aluminum oxide films deposited
by spray pyrolysis
M. Aguilar-Frutis
Physics Department, CINVESTAV IPN, Apdo. Postal 14-740, 07000 Mexico DF, Mexico
M. Garcia
IIM, UNAM, Coyoacan 04510, Mexico DF, Mexico
C. Falcony
PMCATA and Physics Department, CINVESTAV IPN, Apdo. Postal 14-740, 07000 Mexico DF, Mexico
͑
Received 8 October 1997; accepted for publication 10 February 1998͒
The optical and electrical characteristics of spray pyrolysis deposited aluminum oxide films are
reported. The films were deposited from a spraying solution of aluminum acetylacetonate in
N,N-dimethylformamide using an ultrasonic mist generator on ͑100͒ Si substrates. The addition of
water mist during the spraying deposition process resulted in an overall improvement of the films
characteristics. The substrate temperature during deposition was in the 450–650 °C range.
Deposition rates up to 90 Å/s were obtained depending on the spraying solution concentration and
substrate temperature with an activation energy of the order of 31 kJ/mol. The optical energy band
gap for these films was 5.63 eV and the refractive index at 630 nm up to 1.66 was measured by
ellipsometry. The electrical characteristics of the films were determined from the capacitance and
current versus voltage measurements of metal–oxide–semiconductor ͑MOS͒ structures
1
1
incorporating them. A dielectric constant of 7.9, interface states density of the order of 10
2
ϫ1/eV cm as well as breakdown fields higher than 5 MV/cm were determined in this way.
©
1998 American Institute of Physics. ͓S0003-6951͑98͒03514-1͔
Aluminum oxide films deposited by a wide range of
deposition techniques have been evaluated for their applica-
tion as dielectric layers on different types of microelectronic
scribed in detail previously.5,6 It consists of an ultrasonic
generator used for mist generation from a spray solution. The
mist is transported through a glass tube to the substrate sur-
face which is being heated to achieve the pyrolysis reaction.
For this work, aluminum acetylacetonate dissolved in
N,N-dimethylformamide has been used as a spraying solu-
tion. The concentration of this solution was varied from 1 to
12 gm of aluminum acetylacetonate in 100 ml of dimethyl-
formamide. Some of these samples were deposited by adding
a stream of water mist in parallel to the spraying solution.
The films were deposited on n-type silicon wafers of 0.1 ⍀-
cm and on quartz slides for the optical absorption measure-
ments to a thickness in the range of 900–1300 Å. For the
electrical measurements MOS structures were fabricated by
thermally evaporating aluminum contacts with an area of
1.1ϫ10 cm on top of the aluminum oxide film deposited
on the silicon substrates. The silicon substrates were given
the standard RCA cleaning procedure before the deposition
process. Substrate temperatures in the range of 450–650 °C
were used during film deposition. Thickness and refractive
index were measured with a manual ellipsometer at 630 nm.
The optical absorption measurements were performed with a
commercial ultraviolet-visible ͑UV-Vis͒ spectrophotometer
in the 190–900 nm range. Commercial automated equipment
was used for the capacitance and current versus voltage mea-
surements.
1
,2
devices. In particular the high chemical stability, high ra-
diation resistance, high thermal conductivity and low perme-
ability to alkali impurities that these films present make them
good candidates for application on metal–oxide–
semiconductor ͑MOS͒ structures as gate oxides among sev-
eral other applications such as passivation layers, and dielec-
tric films in chemical sensors.3 All these applications
required films with good homogeneity and low surface
roughness and good control of thickness for films of the
order of 1000 Å thick or less. Also good dielectric charac-
teristics and density of the films are required for such appli-
cations. Spray pyrolysis is a deposition technique which is
frequently used for film deposition on applications that re-
quire large area, low cost processes. However it is not re-
garded as a technique with a large degree of control when
thin films below 1000 Å are required. In the present work we
report the deposition of thin aluminum oxide films using the
spray pyrolysis technique in which excellent control of thick-
ness homogeneity and surface roughness has been achieved
for films of the order of 1000 Å or less. The optical charac-
teristics of these films indicate a dense material with a re-
,4
Ϫ2
2
fractive index of 1.66. An activation energy (E ) of the order
a
of 31 kJ/mol was determined from the deposition rates at
different substrate temperatures. These films have good di-
electric characteristics with a dielectric constant of the order
of 7.9 and they are able to stand electric fields up to 5
MV/cm without destructive breakdown.
The aluminum oxide films were deposited at different
spraying solution concentrations and at different tempera-
tures. The activation energy for the deposition process (Ea)
was determined by plotting the deposition rate (R ) as a
d
The spray pyrolysis deposition system has been de-
function of the reciprocal substrate temperature (1/T ) in a
s
0003-6951/98/72(14)/1700/3/$15.00
1700
© 1998 American Institute of Physics
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Aguilar-Frutis
