Southern
Taiwan
University
先進奈米科技暨
應用光電實驗室
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Silicon nano-crystalline structures fabricated by a sequential
plasma hydrogenation and annealing technique
Y. Abdi a,1, P. Hashemi a,1, S. Mohajerzadeh a,*, M. Jamei a,1,
M.D. Robertson b, M.J. Burns b, J.M. MacLachlan b
a
Thin Film and Nano-Electronic Laboratory, Nano-Electronics Center of Excellence,
University of Tehran, Tehran, Iran
b Department of Physics, Acadia University, Wolfville, Nova Scotia, Canada B4P 2R6
Student：Jen-Chieh Cheng
Professor：Chih-Cheng Kao
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OUTLINE
• Introduction
• Experiments
• Results and discussion
– SEM
– PL Spectrum
– FTIR Spectrum
– TEM
– HREM
• Conclusions
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Introduction
• Nano-crystalline,porous silicon(PS) films are
promising materials in the areas of optoelectronics
and microelectronics due to their visible
luminescence characteristics at room temperature.
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Experiments
• Step1:N-type(100)silicon substrates with a resistivity of 15 Ω-cm were cleaned in standard RCA #1 solution
(NH4OH/H2O2/H2O=1:1:5),rinesd with deionized water
and blow dried in air.
• Step2:The samples were then coated with about 100nm
of thermally grown silicon dioxide at a temperature of
1100℃.
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• Step3:A 100nm thick layer of amorphous silicon was then
deposited using an E-beam evaporation system with the
substrate temperature kept at 300℃and a base pressure of
1.3×10-4 Pa.
• Step4:The amorphous silicon-coated substrates were then
placed in a direct-current plasma-enhanced-chemicalvapor-deposition (dc-PECVD) system to perform the
hydrogenation–annealing sequence.
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• Step5:Specimens were prepared for plasma power
densities ranging between 4.5 W/cm2 and 6.5 W/cm2 and
substrate temperatures ranging between 350 °C and 450 °C
for 30 min.
• Step6:The subsequent annealing step was conducted insitu at a substrate temperature 70 °C higher than what was
used for the hydrogenation step for a period of 35 min and
three successive hydrogenation–annealing steps were
applied to each of the samples.
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• Step7:During the hydrogenation step, the pressure of the
reactor was maintained at 200 Pa and the hydrogen flow
was set at 20 sccm.
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dc-PECVD system
100nm
100nm
A schematic drawing of the hydrogenation process in a dc-PECVDsystem.
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PECVD reactions system
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Quantum confinement effects
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Result of SEM
SEM images of the surface of silicon hydrogenated at a power density of
6.5 W/cm2 for 15 min and at temperatures of (left) 350 °C and (right) 400 °C.
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Result of SEM
SEM images of the surface of silicon hydrogenated at temperature of 400 °C for
30 min and at plasma power densities of (left) 3.5 W/cm2 and (right) 4.5 W/cm2.
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Result of PL spectrum
Collection of PL spectra from samples prepared at three temperatures of 350 °C, 375 °C and
400 °C and different plasma power densities during hydrogenation of 4.5 W/cm2 and 6.5
W/cm2. By raising the temperature a blue shift in the peak of the emitted light is observed
while higher plasma powers result in a reduction in the light intensity.
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Result of FTIR spectrum
FTIR spectrum of a sample prepared on a silicon substrate without an interfacial oxide
showing the presence of Si–O bonds. No clear evidence of Si–H is observed although a
trace of Si–O–H bonds is visible in this image.
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Result of TEM
(a) Dark-field TEM image of a sample prepared at 350 °C at a plasma power
density of 6.5 W/cm2 with the associated SADP inset.
(b) Grain size distribution histogram as measured from the dark-field image.
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Result of TEM
(a) Dark-field TEM image of a sample prepared at 400 °C with a power density
of 6.5 W/cm2, and the associated (b) grain size distribution histogram.
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Result of TEM and HREM
(a) Bright-field and (b) dark-field cross-sectional TEM images of a sample prepared at
400 °C with a plasma power density of 4.5 W/cm2. A selected area electron diffraction
pattern of the sample was inserted in part (a)showing the ring pattern characteristic of
a polycrystalline structure. The rectangle in part (b) represents the location of the
high-resolution electron microscopy (HREM) image provided in part (c). (c) An HREM
image showing Si {111} lattice fringes of the nano-sized silicon grains.
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A plot of the PL peak emission wavelength against the peak in the average grain
diameter distribution. The error bars are the standard deviations of the grain
diameter distributions.
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Rusult of lithography
An optical image of the light-emitting behavior of patterned nanocrystalline porous Si
under UV illumination showing the words “Thin Film”, as inserted in a box in the image.
The patterning of this structure has been achieved by standard photolithography using
positive resists. After patterning and developing the resist, the thin silicon film was
removed by chemical etching.
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Conclusions
• In summary, we report a method for the
fabrication of nanocrystalline porous silicon from
a deposited amorphous silicon layer. The
energetic hydrogen ions result in the formation
of nano-sized grains which in turn leads to the
creation of porous layers.
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• We believe that in the process of hydrogenation ,
hydrogen radicals replace the dangling bonds of the
silicon atoms in the amorphous structure and when
depassivating the previously hydrogenated bonds,
energy is transferred to the silicon atom enhancing
the chance for nucleation and growth of the nanocrystals.
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• Higher processing temperatures would lead to
samples with a smaller average grain size, whereas
lower plasma power densities resulted in more
packed structures with a smaller surface structure
size.
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Thanks for your attention
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