Nanofabrication of high aspect ratio structures using an evaporated resist containing metal

Abstract

Organic electron beam resists are typically not resistant to the plasma etching employed to transfer the pattern into the underlying layer. Here, the authors present the incorporation of a metal hard mask material into negative resist polystyrene by co-evaporation of the polystyrene and the metal onto a substrate. With a volume ratio of 1:15 between Cr and polystyrene, this nanocomposite resist showed an etching selectivity to silicon one order higher than pure polystyrene resist. Silicon structures of 100 nm width and 3.5 μm height (aspect ratio 1:35) were obtained using a non-switching deep silicon etching recipe with SF6 and C4F8 gas. Moreover, unlike the common spin coating method, evaporated nanocomposite resist can be coated onto irregular and non-flat surfaces such as optical fibers and AFM cantilevers. As a proof of concept, we fabricated high aspect ratio structures on top of an AFM cantilever. Nanofabrication on non-flat surfaces may find applications in the fields of (AFM) tip enhanced Raman spectroscopy for chemical analysis and lab-on-fiber technology.

Fabrication of silicon nanostructures with large taper angle by reactive ion etching

“…1(b)], starting from the standard Bosch process, several research groups have developed silicon etching recipes that give vertical profile and are capable of etching ultrahigh aspect ratio nanostructures. [12][13][14][15] Those recipes have either no or very small sidewall scallop depending on whether it is a nonswitching process or a switching one yet with very short cycle time. For our work, we chose the recipe reported in Ref.…”

“…This recipe is a nonswitching deep silicon etching process using SF 6 and C 4 F 8 gas for, respectively, etching and passivation, and it was previously employed to etch high aspect ratio silicon structures of 100 nm width and 3.5 lm height (aspect ratio 1:35). 13 One can generally obtain tapered profile by promoting inhibitor (here fluorocarbon polymer) formation and decreasing its removal rate, which can be realized by increasing the ratio of C 4 F 8 /SF 6 , reducing the RF bias power or substrate temperature, and/or increasing the gas pressure. In the experiment, we systematically reduced the C 4 F 8 /SF 6 gas flow ratio from the starting point of 38/22 to 59/1 (total gas flow was fixed at 60 sccm) and the RF bias power from 20 to 10 W, while keeping the other parameters fixed.…”

Batch fabrication of AFM probes with direct positioning capability

“…8 With the optimal ratio of SF 6 /C 4 F 8 ¼22:38, a smooth vertical etching profile can be obtained, with a silicon etching rate of 390 nm/min and a high etching selectivity between Si and Al of 100:1. 9 Next, the probes were dipped into 1:20 diluted hydrofluoric (HF) acid for 2 min to remove the remaining Al layer.…”

Chromium oxide as a hard mask material better than metallic chromium

“…5 Alternatively, metal Cr can be incorporated physically into polystyrene (PS) resist using cothermal evaporation. 6 A more popular approach to etch deep into the substrate is to use conventional polymer resist combined with an intermediate hard etching mask, where the intermediate hard mask is first patterned by lithography and pattern transferring, and then the substrate or sublayer is dry etched using the patterned hard mask structure as etching mask. Chromium (Cr) is probably the most widely utilized hard mask material for plasma etching because of its high selectivity to silicon and its compound when using fluorine or chlorine based etching chemistry.…”