自上而下(Top-down)方法实现高密度垂直硅纳米线(Vertical Si NWs)阵列

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Fig.1.SEM images (titled view)of HSQ nanocolumns networks with a height of 130nm (a–c)and 300nm (d),and a diameter/pitch of (a)21nm/100nm,(b)36nm/30nm,(c)30nm/25nm,(d)80nm/60nm,respectively.

of negative-tone resist Hydrogen SylsesQuioxane (HSQ)diluted in isobutyl ketone marketed by Dow Corning under name of FOx-12and FOx-16was used.The HSQ solution was spin coated on (100)Si wafers and baked at 80 C for 60s to evaporate the solvent.Resist thicknesses rang-ing from 70nm to 330nm have been obtained by spin-coating at various angular speeds.E-beam exposures are performed with an EBPG 5000+system from LEICA at the high energy of 100K eV .100pA beam current gives an extremely small spot size,estimated at 5nm.An opti-mum dose of 2750 C/cm 2coupled with correction fac-tors that take into account proximity effects and pattern sizes generate HSQ nanocolumns networks with diame-ters ranging from 20nm to 240nm.After exposure,the HSQ resist was developed by manual immersion in 25%Tetramethylammonium Hydroxide (TMAH)at 20 C for 60s,rinsed in deionized water,and blown dry with ing this process sequence,HSQ nanopillars net-works with very high contrast are obtained as shown in

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2.SEM images (cross-section view)of Si nanoblade using 100 nm

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Fig.3.(a)SEM image (cross-section view)of network of 30nm length nanoblades with a spacing of 60nm,100nm and 180nm and (b)zoom of the densest part (c)schematic representation of species scattered from the resist mask.(d–e)SEM images (titled view)of Si NWs network etched with two different resist thicknesses.

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Fig.4.SEM images(titled view)of(a)a large area(22 m×22 m) of vertical Si NWs networks with a100%yield;(b)ultra high density (4×1010cm−2)vertical Si NWs networks with a100%yield.

performed on a dense network of HSQ nanocolumns,as shown in Figure3(d).The same phenomenon is observed with a shape of nail head in the top part of the Si NWs. In order to realize dense networks of vertical Si NWs with a limited undercut,a sufficient resist height should remain until the end of the process as presented in Figure3(e).In summary,using the optimized RIE conditions applied on dense HSQ columns,ultra high density vertical Si NWs networks were demonstrated.Figure4(a)shows SEM view

NWs without any defects and

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Fig.5.SEM image(titled view)of vertical Si NWs networks tapered wet oxidation with11.7nm diameter and a high aspect ratio of11.