1063-7397/02/3102- $27.00 © 2002 MAIK “Nauka /Interperiodica”
0084
Russian Microelectronics, Vol. 31, No. 2, 2002, pp. 84–87. Translated from Mikroelektronika, Vol. 31, No. 2, 2002, pp. 99–103.
Original Russian Text Copyright © 2002by Mittova, Tomina, Sukhochev, Prokin, Vasyukevich.
INTRODUCTION
Previous research has revealed that using
d
-block
elements and their compounds as oxidation promoters
of III–V semiconductors, such as GaAs, offers much
room to manipulate the growth mechanism and, hence,
the properties of oxide films [1–3]. Thermal oxidation
strongly depends on whether the promoter is fed at a
limited or unlimited rate.
The present experimental study addresses solid-
phase reactions in the thermal oxidation of GaAs cov-
ered with an Ni layer.
EXPERIMENTAL CONDITIONS
The Ni/GaAs heterostructures were fabricated from
GaAs(100) wafers (SAGOCh-1) whose surface was
treated with a 49% hydrofluoric acid for ten minutes and
repeatedly rinsed in distilled water. The Ni layer was
deposited by thermal evaporation (at
2.7
×
10
–6
mmHg)
using a VUP-5 exhaust unit. The original Ni purity was
98.9%. It was measured with a VRA-30 x-ray fluores-
cence analyzer, which has a sensitivity of
10
–2
–10
–4
%
and is accurate to within 1% or so. Ni thickness was
found to be
50
±
5
nm. This was determined with an
MII-4 interference microscope.
The heterostructures were oxidized in the continu-
ous quartz reactor of a horizontal-tube resistor furnace,
the process temperature controlled with a BPRT-1 unit
(accurate to within
±
2°
C). Oxidation was carried out in
air at
450–530°ë
during 5–50 min. The oxide films
were grown by a reoxidation technique, with which the
entire isothermic thickness–time characteristic is
obtained from a single specimen. Oxide thickness was
measured with an LEF-3M ellipsometer (accurate to
within
±
1
nm).
RESULTS AND DISCUSSION
The kinetics of thermal oxidation was modeled with
the equation
d
= (
k
τ
)
n
, where
d
is the oxide thickness
(nm),
k
is the effective rate constant (nm
1/
n
min
–1
), and
τ
is the oxidation time (min). The isothermic thickness–
time characteristics for the oxidation are shown in Fig. 1.
Kinetic data were derived according to Mittova
et al.
[4] and are collected in Table 1.
The fact that
n
av
< 0.5 implies that the oxidation is
governed by diffusion-limited solid-phase reactions
[5]. Since the curves are free from kinks, we can infer
that the oxidation mechanism does not change with
time. The effective activation energy (EAE) was found
to be 317 kJ/mol, a value higher than that for the oxida-
tion of bare GaAs (110 kJ/mol). The reason is that the
respective major processes are different in character
from each other, which accords with previous findings
concerning the oxidation of Ni/InP [3].
The oxide films were also examined by IR spectros-
copy, ultrasoft-x-ray emission spectroscopy, and x-ray
diffractometry.
The IR-spectroscopy study (Fig. 2) was carried out
over the range 400–1400 cm
–1
, using a UR-10 two-beam
spectrophotometer. It was found that the oxide films are
mainly composed of Ga
2
O
3
(475 and 525 cm
–1
) [6] and
NiO (560 and 825 cm
–1
). All specimens exhibited the
Solid-Phase Reactions in the Thermal Oxidation
of Ni/GaAs Heterostructures
I. Ya. Mittova, E. V. Tomina, A. S. Sukhochev, A. N. Prokin, and A. O. Vasyukevich
Voronezh State University, Voronezh, Russia
Received October 15, 2001
Abstract
—The thermal oxidation of GaAs covered with an Ni layer is studied experimentally. It is shown that
this layer makes for better dielectric performance of the oxide film and inhibits the escape of the volatiles from
GaAs. A possible pattern of the oxidation of Ni/GaAs heterostructures is put forward. It includes the formation
of a transition layer between NiO and GaAs, which contains nickel–arsenic and nickel–gallium compounds.
Reactions at the interface between the transition layer and NiO are considered.
Table 1.
Kinetic data on the thermal oxidation of Ni/GaAs
T
,
°
C
n
± ∆
nn
av
± ∆
n
av
450 0.40
±
0.01
0.35
±
0.03
470 0.48
±
0.04
490 0.31
±
0.04
510 0.30
±
0.01
530 0.28
±
0.03
EAE, kJ/mol 317
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