Preparation of Silicon Nanowire Arrays by Etching
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Transcript of Preparation of Silicon Nanowire Arrays by Etching
METAL-ASSISTED CHEMICAL ETCHING OF SILICON:
PREPARATION OF SILICON NANOWIRE ARRAYS
Elisabeth Galopin, Gaëlle Piret, Yannick Coffinier, Sabine Szunerits and Rabah Boukherroub
Institut de Recherche Interdisciplinaire (IRI) USR-3078
Institut d’Electronique de Microélectronique et de Nanotechnologie (IEMN), CNRS-8520
Villeneuve d’Ascq, France.
Topic : Integration and synthesis of new materials
The paper reports on the preparation of SiNW
arrays and patterns using the chemical etching
method of crystalline silicon substrate. Electroless
deposition of silver nanoparticles onto the silicon
nanowires was further exploited for the
preparation of highly sensitive Surface Enhanced
Raman Spectroscopy (SERS) substrates.
I. INTRODUCTION
In recent years, a great deal of effort has been made to
the fabrication of one-dimensional nanostructured materials
owing to their submicron ultimate feature size and
dimensionally dependent physical properties for future use
in nanodevices [1]. Silicon is the basic material in
microelectronics, and silicon nanowires (SiNW) and
nanowire arrays have attracted much attention for their
potential applications in the field of silicon nanoelectronics
and use the SiNWs as nanocomponents to build nano
circuits and nanobiosensors [2].
II. SILICON NANOWIRE FABRICATION
A. Metal Assisted Ckemical Etching
Various methods have been developed to prepare one-
dimensional silicon nanostructures [1, 2]. Even though the
techniques offer a good control over the nanostructures
dimensions, most of the methods require high temperatures
or a high vacuum, templates and complex equipment.
Metal-assisted chemical etching of silicon has been used
in the past for the preparation of porous silicon substrates
[3]. The technique has successfully been applied for the
fabrication of large-area aligned SiNW arrays on single
crystal silicon wafers [4-6].
Silicon wafers with different doping levels were used in
the study. The surface was first degreased in acetone and
isopropanol, rinsed with Milli-Q water and then cleaned in
a piranha solution (3:1 concentrated H2SO4/30% H2O2) for
15 min at 80°C followed by copious rinsing with Milli-Q
water. The SiNW arrays were prepared by chemical
etching of the clean substrate in HF/AgNO3 (5.25./0.02 M)
solution at 50°C for a given time. Fig. 1 displays a SEM
image of the resulting surface. It consists of SiNW arrays
wrapped by dendrites. The energy dispersive X-ray
spectroscopy shows that these dendrites are composed of
silver (Fig. 2).
Figure 1. SEM image of branched silver dendrites formed on Si sample
after etching in HF/AgNO3 aqueous solution at 50°C for 10 min.
Figure 2. Energy dispersive X-ray image of silver dendrites formed on
Si sample by etching in HF/AgNO3 aqueous solution at 50° C for 10 min.
The electroless deposition of Ag and silicon etching in
the fluoride solution containing Ag+ occurs according to
the following equations:
Si + 4h+ + 4HF SiF4 + 4H+
SiF4 + 2HF H2SiF6
Ag+ + 1e- Ag
Chemical removal of the silver deposits using a mixture
of HCl/HNO3/H2O (1/1/1) at room temperature led to the
formation of well-aligned SiNW arrays (Fig. 3).
Figure 3. Cross-sectional SEM image of the silicon nanowire array
formed by chemical etching of Si(100) in HF/AgNO3 aqueous solution at
50°C for 10 min.
By combining optical lithography and chemical etching,
we have successfully prepared SiNW patterns in a
controllable fashion. The choice of the resist that is stable
in HF/AgNO3 aqueous solution is the key step in this
process.
B. Silver nanoparticles deposition
We then have used the electroless technique for the
deposition of silver nanoparticles onto the silicon nanowire
arrays. The nanoparticles were obtained by dipping the
silicon nanowires 1min in HF/AgNO3 (0.26/5.10-4 M) at
room temperature (Fig. 4).
Figure 4. Electroless technique for the deposition of silver nanoparticles
onto the silicon nanowire arrays.
III. CONCLUSION
We successfully prepared silicon nanowire arrays using
the chemical etching method for crystalline sililcon
substrate. These surfaces were then covered by silver
nanoparticles by electroless deposition. Finally, we
investigated the surface-enhanced Raman Scattering
(SERS) performances of the resulting structure. The
performance of the substrate was demonstrated for Rh6G
concentrations down to 1x10-9 M.
ACKNOWLEDGMENT
The authors would like to acknowledge FEDER (Fonds Européen de DEveloppement Régional) who supported this work by equipment contribution.
REFERENCES
[1] Rao, C. N. R.; Deepak, F. L.; Gundiah, G.; Govindaraj, A. Prog.
Solid State Chem. 2003, 31, 5–147.
[2] Hu, J.; Odom, T. W.; Lieber, C.M. Acc. Chem. Res. 1999, 32, 435.
[3] Li, X.; Bohn, P. W. Appl. Phys. Lett. 2000, 77, 2572.
[4] Peng, K.; Wu, Y.; Fang, H.; Zhong, X.; Xu, Y.; Zhu, J. Angew. Chem.,Int. Ed. 2005, 44, 2737-2742.
[5] Peng, K.; Fang, H.; Hu, J.; Wu, Y.; Zhu, J.; Yan, Y.; Lee, S. T. Chem.-Eur. J. 2006, 12, 7942-7947.
[6] Piret, G.; Coffinier, Y.; Roux, C.; Melnyk, O.; Boukherroub, R. Langmuir 2008, 24, 1670-1672.