Substrate dependence on the optical properties of Al2O3 films grown
by atomic layer deposition
Y. Kim, S. M. Lee, C. S. Park, S. I. Lee, and M. Y. Lee
Process Development Group 2, Process Development Team, Semiconductor R&D Center, Samsung
Electronics Co., San #24, Nongseo-Lee, Kiheung-Eup, Yongin-Si, Kyungki-Do, 449-900, Korea
͑Received 4 September 1997; accepted for publication 17 October 1997͒
The atomic layer deposition technique has been applied to the growth of Al2O3 thin films on the
substrates of Si͑100͒, 100-nm-thick SiO covered Si͑100͒ SiO /Si͑100͒ , and 90-nm-thick TiN
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2
2
covered SiO2 /Si͑100͒. The growth rate of Al2O3 films was 0.19 nm/cycle and identical for all
substrates employed under the surface controlled process. However, the optical properties of Al2O3
films were significantly affected by different substrates. The average interband-oscillator energy and
refractive index parameter were determined to be 3.330 eV and 2.992ϫ10Ϫ14 eV m2 for Al2O3 film
grown on Si͑100͒, while those for the film grown on SiO2 /Si͑100͒ were 4.492 eV and 2.074
ϫ10Ϫ14 eV m2, respectively. © 1997 American Institute of Physics. ͓S0003-6951͑97͒00451-8͔
maintained at 150 °C to minimize reactant condensation. The
Al2O3 has many promising properties such as very low
permeability of alkali ions and other impurities,1 high radia-
tion resistance,2 relatively high dielectric constant,3 high
thermal conductivity,4 and transparency over wide range of
wavelength. Because of these properties, many attentions
have been paid to the study of Al2O3 films, which showed
promising results as gate oxides5 and interpoly dielectrics6 in
memory devices, insulating layers7 in electroluminescent dis-
play devices, waveguides,8 and corrosion-resistant coating
films9 on metals. The growth of Al2O3 films has been con-
ducted by molecular beam epitaxy ͑MBE͒,10 chemical vapor
deposition ͑CVD͒,11 plasma-enhanced metalorganic chemi-
cal vapor deposition ͑PE-MOCVD͒,12 reactive sputtering,6
and atomic layer deposition ͑ALD͒.13 Concerning the re-
quirements of the thin film growth such as uniformity, con-
formality, low-temperature processing, and exquisite thick-
ness control, ALD is known as the most adequate
technique13 because of its nature of surface controlled pro-
cess, where the substrate surface is alternately exposed to the
appropriate precursor fluxes. However, several issues should
be addressed before ALD technique will replace conven-
tional methods, although it offers distinct advantages. The
factors that define and limit growth phenomena reflect the
underlying surface reactions. Recently, the chemical reac-
tions on the surface have been investigated in detail.13,14
However, the effects of underlayers on the growth rate and
optical properties of Al2O3 film have not been reported yet.
In the present work, ALD technique has been applied to
the growth of Al2O3 films exhibiting superior conformality
and uniformity. The dependence of the film growth and of
the optical properties of Al2O3 on various substrates has been
investigated.
process pressure was maintained at 230 mTorr during the
dosing of vaporized precursors and 200 mTorr during the
purging. Purified Argon with the flow rate of 100 sccm was
utilized as the diluting and purging gas during the precursor
dosing and purging step, respectively. Prior to the growth of
Al2O3 films, the native oxide covered substrate, Si͑100͒, was
cleaned by the conventional wet chemical treatment and di-
luted HF etching treatment in sequence for the removal of
particles and native oxides, respectively. The surface of Si
wafer prepared in this manner is known to be contamination-
free and terminated with atomic hydrogen. The time for one
cycle during the deposition of Al2O3 was composed of 1, 14,
1, 14 s corresponding to the dosing of TMA, purging of
excess TMA and by-products, dosing of DIW, and purging
of excess DIW and by-products. The chemical composition
of Al2O3 was determined to be stoichiometric by Rutherford
backscattering spectroscopy ͑RBS͒. The crystallographic
structures of the films were confirmed to be amorphous re-
gardless of those of substrates by x-ray diffraction methods
using a Rigaku RU 300 diffractometer.
Surface morphology, conformality, and film thickness
were examined by high-resolution scanning electron micro-
scope ͑SEM͒. Optical constants, including refractive index
and extinction coefficient, and thickness of film were deter-
mined by UVISEL spectroscopic phase modulated ellipsom-
eter ͑SPME͒.
In comparison to the conventional deposition methods
such as sputtering and CVD, ALD is considered as a digital
process since it does not require a precise control of analog
parameters such as growth time and reactant flux. The digital
nature of the ALD growth process is best illustrated by the
linear dependence of the deposited film thickness on the
number of deposition cycles. In addition, ALD is a surface
controlled process, which can be confirmed by the perfect
conformality of the deposited films. The substrate depen-
dence on the growth rate of Al2O3 films was investigated
using three different substrates. The substrates employed
were Si͑100͒, 100-nm-thick SiO2 film covered Si͑100͒
SiO /Si͑100͒ , and 90-nm-thick TiN film covered
In all cases, the film deposition process was carried out
in a vertical, warm wall reactor vessel with a shower head
and a resistively heated susceptor. Trimethylaluminum
͑TMA͒, Al͑CH3͒3, and distilled water vapor ͑DIW͒, H2O,
were used as the chemical precursors to provide Al and O to
the growing surface. It is well known that reactions of TMA
with DIW to form Al2O3 and CH4 are highly exothermic and
occur readily with a low activation energy.5 The substrate
temperature was fixed at 370 °C, while the chamber wall was
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2
Ti/SiO2 /Si͑100͒ TiN/Ti/SiO /Si͑100͒ , where crystallo-
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2
3604
Appl. Phys. Lett. 71 (25), 22 December 1997
0003-6951/97/71(25)/3604/3/$10.00
© 1997 American Institute of Physics
Kim
