Highly ordered hexagonally arranged nanostructures on silicon through a self-assembled silicon-integrated porous anodic alumina masking layer (original) (raw)
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Nanoscale Research Letters, 2013
We report on Si nanopatterning through an on-chip self-assembled porous anodic alumina (PAA) masking layer using reactive ion etching based on fluorine chemistry. Three different gases/gas mixtures were investigated: pure SF 6 , SF 6 /O 2 , and SF 6 /CHF 3 . For the first time, a systematic investigation of the etch rate and process anisotropy was performed. It was found that in all cases, the etch rate through the PAA mask was 2 to 3 times lower than that on non-masked areas. With SF 6 , the etching process is, as expected, isotropic. By the addition of O 2 , the etch rate does not significantly change, while anisotropy is slightly improved. The lowest etch rate and the best anisotropy were obtained with the SF 6 /CHF 3 gas mixture. The pattern of the hexagonally arranged pores of the alumina film is, in this case, perfectly transferred to the Si surface. This is possible both on large areas and on restricted pre-defined areas on the Si wafer.
Nanotechnology, 2005
Ultra-thin alumina films with self-ordered cylindrical vertical pores were fabricated on a p-type silicon substrate by anodization of Al films with thickness in the range of 30-500 nm in sulfuric or oxalic acid aqueous solutions. In both cases the pores were arranged in hexagonal cells in a close-packed structure and their diameter and density depended on the electrochemical solution used. In the case of sulfuric acid both 30 and 500 nm Al films resulted in a similar uniform porous structure using exactly the same anodization conditions for both thicknesses, the pore diameter being in the range of 10-30 nm and their density of the order of 6-8 × 10 10 pores cm −2 . In the case of oxalic acid the 500 nm thick films resulted in a uniform porous structure with larger pores than in sulfuric acid, of diameter in the range of 20-40 nm and a density of the order of ≈10 10 pores cm −2 . On the other hand, with oxalic acid it was impossible to form a uniform porous structure from the 30 nm thick Al film at the same conditions as used for the 500 nm thick film. Plan-view and cross-sectional transmission electron microscopy was used to investigate systematically the structure and morphology of the alumina films. Cross-sectional TEM images showed that the alumina/Si interface was sharp, but a void was observed beneath each pore, separated from the pore by a thin alumina layer. The same structure was obtained with both electrolytes. The effect of pre-annealing of the Al films on the anodic alumina layers was also investigated in detail.
Synthesis of High Density, Size-Controlled Si Nanowire Arrays via Porous Anodic Alumina Mask
Chemistry of Materials, 2006
Porous anodic alumina (PAA) masks are employed for the template synthesis of high density silicon nanowire (SiNW) arrays on a silicon substrate by the vapor-liquid-solid method. The uniform-sized ordered arrays of nanopores in the PAA mask anchored to Si(111) substrate are shown to enable the realization of vertically aligned epitaxial SiNWs with uniform diameter and spacing. The average diameter of the wires is 72 nm while the density is 60 wires/µm 2 . The high packing density and tightly controlled dimensions of SiNWs obtained by this nonlithographic method allow their effective integration into nanodevices for mass production.
Fabrication of Porous Silicon Microstructures using Electrochemical Etching
2000
In this work an equipment was built and tested for the electrochemical etching of silicon in hydrofluoric acid electrolyte using aluminium anode and stainless steel cathode. Porous silicon layer was fabricated in n-type (100) oriented silicon using solution HF : H 2 O : C 2 H 5 OH, 2 : 1 : 1 by volume. It was revealed, that current density determines geometry of the pores and etching anisotropy. Average depth of the obtained pores varied from 16 µm to 27 µm, when width of the pores varied from 2 µm to 5 µm. The depth of pores depended slightly on the current density, and anisotropy was high in the case of small diameter of the pores.
Investigation of formation processes of an anodic porous alumina film on a silicon substrate
Applied Surface Science, 2004
We investigated formation processes of a porous anodic alumina film on a p-type silicon (Si) substrate using infrared absorption spectroscopy in the multiple internal reflection geometry (MIR-IRAS). We observed drastic IR spectral changes when anodization took place near the interface between an aluminum (Al) layer and a Si substrate. The intensity of absorption peaks due to porous anodic alumina increased with a decrease in anodic current density and it decreased simultaneously with formation of silicon oxides (SiO 2 ) at the interface between a porous anodic porous alumina film and a Si substrate after appearance of a spike of anodic current density which indicated changes of states of electric double layer at the interface between an electrolyte and an electrode due to contact between an electrolyte and a Si substrate. The results suggested that the formation of SiO 2 nanodots on a Si substrate promoted penetration of electrolytes to peel the porous anodic alumina film from it. #
Alumina nanotemplate fabrication on silicon substrate
Nanotechnology, 2004
ABSTRACT Alumina nanotemplates integrated on silicon substrate with pore diameters of 12–100 nm were prepared by galvanostatic (constant current) anodization. High current density (e.g. 100 mA cm−2) promoted a highly ordered hexagonal pore structure with fast formation rate independent of anodizing solution. Alumina formation rates of 2000 and 1000 nm min−1 were achieved at current densities of 100 and 50 mA cm−2, respectively. These rates were approximately two orders of magnitude greater than other reports in the literature. Different electrolytes of sulfuric acid (1.8–7.2 M), oxalic acid (0.3 M) and mixed solutions of sulfuric and oxalic acids were evaluated as anodizing solutions. At fixed current density, sulfuric acid promoted smaller pore diameter with lower porosity than mixed acids and oxalic acid. The I–V characteristics of aluminium anodization show the measured voltages at given current densities strongly depend on solution composition, operating temperature, and bath agitation. The pore diameter of the silicon-integrated alumina nanotemplate varied linearly with measured voltage with a slope of 2.1 nm V−1, which is slightly smaller than reported data.
Independently addressable fields of porous anodic alumina embedded in SiO2 on Si
Applied Physics Letters, 2008
Fields of thin-film porous anodic alumina (PAA) are fabricated within a SiO2 support and on independently addressable underlying metal pads. The underlying metallization provides a means for unique postprocessing to be performed on the PAA fields. Customized postprocessing is demonstrated with the synthesis of single-walled carbon nanotubes (SWCNTs) from an embedded catalyst in the PAA, followed by selective decoration of the SWCNTs from different PAA fields with dissimilar nanoparticles. Achieving uniquely functionalized fields of PAA on a single chip provides a scalable integration platform to be used in multiplexed chemical and biological sensing or nanoelectronic devices.