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D. RATHEE ET AL.
prepared by mixin g TIP with absolute ethanol an d acetic
acid in the molar ratio of 0.1:8:0.1. The substrate was
placed on spinner and drops of above mentioned solution
were placed on substrate. The substrate was then allowed
to spin for 2 minutes with spinning rate 1500 rpm. Then
sample was baked for 20 minutes at 95˚C. The film was
than annealed in dynamic air at 550˚C for 30 minutes to
treat the adsorbed film. While SiO2 film was grown on
silicon substrate us ing dry oxidation process at 650˚C fo r
60 minutes with a pre ramp of 5˚C per minute so that we
reach reached to 950˚C and than flat temp of 950˚C for
the 110 minutes at last post-ramp of 5˚C per minutes for
60 minutes with N2(12) and O2(32).
2.2. MOS Capacitor Fabrication
MOS capacitors were fabricated on a 4 inch diameter &
800 micron thick N-type silicon wafer. The dielectric
layer of 510 Å was grown on silicon wafer by dry oxida-
tion at 950˚C for 2 hours. About 3000 Å of aluminum
was then deposited over oxide layers using the sputtering
technique. The 10–2 cm2 capacitor contact was defined by
physical mask. The contacts were annealed in gas at-
mosphere H2, & N2 at 350˚C for 25 minutes. The fabri-
cated capacitors electrically tested to characterize the
material and to inspect the device performance. The
variation of capacitance (C) with voltage VG ranging –5
Volts to +5 Volts is shown in Figure 2.
In this work MOS capacitor were fabricated utilizing
TiO2 film deposited by Sol Gel spin coating method and
SiO2 films were thermally grown on <100> silicon sub-
strate. The C-V measurement for TiO2 was obtained us-
ing C-V analyzer [5,6], while SUPREM-III tool was
used for SiO2 layer. SUPREM- III is a computer program
that allows the user to simulate the various processing
steps used in manufacturing of the Silicon integrated or
discrete devices [7]. The characterization of the samples
was carried out at room temperature. Two dimensional
SEM images of the TiO2 film of thickness 52 nm (aver-
age film thickness for three sol-gel immersion cycles)
were obtained (using JEOL-JM-6510 model shown in
Figure 1), the accelerating voltage was kept at 5 kV. The
optical properties were studied using UV-Visible spec-
trophotometer.
3. Results and Discussion
3.1. Film Characetrization
The porous nature of the film is clearly visible. The re-
fractive index (n) of the TiO2 film measured by Ellip-
someter and was found to be 2.33. The optical dielectric
constant can be determined from the refractive index of
TiO2 opt
= n2 = 2.332 = 5.4389. The band gap was
calculated 3.6 eV by using equation
= c/λ,
is pho-
ton energy, c speed of light and λ cut of wavelength by
the help of Spectrophotometer as shown in Figure 1(b).
3.2. MOS Capacitor Results
The variation of the capacitance (C) with gate voltage
(VG) ranging from –5.0 V to +5.0 V with frequency 10
KHz was obtained using SUPREM -III for SiO2 di elec-
tric and by Keithley 590 CV analyzer for TiO2 layer as
shown in Figure 2. The oxide capacitance () is the
high frequency capacitance when the device is biased for
strong accumulation as shown in Figure 2. In case of
SiO2 dielectric it was found to be 5.202 pF, and 41.4 pF
for TiO2 as shown in Figures 2(a) and 2(b) respectively.
ox
C
The dielectric constant of TiO2 (high-k) 80 was ob-
served by calculation from the knowledge of the capaci-
tance (ox ), film thickness (d), the free space charge
permittivity (o
C
) and the area of the capacitor (A) using
the relation K = Cd/ o
A. Thickness was measured by
using stylus profiler and found to be 528 A for TiO2 and
510 A in case of SiO2 Figure 3(a).
While in the inversion region, where the total capaci-
tance per unit area (,mina
C) is the series combination of
the oxide capacitance and the steady minimum depletion
capacitance.
The inversion capacitance per unit area was calculated
(a)
(b)
Figure 1. (a) SEM images of TiO2 deposited on silicon wafer
annealed at 550 C; (b) The absorption spectra of TiO2 t h i n f ilm.
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