Effects of electrons on the shape of nanopores prepared by focused electron beam induced etching

Abstract

The fabrication of nanometric pores with controlled size is important for applications such as single molecule detection. We have recently suggested the use of focused electron beam induced etching (FEBIE) for the preparation of such nanopores in silicon nitride membranes. The use of a scanning probe microscope as the electron beam source makes this technique comparably accessible, opening the way to widespread fabrication of nanopores. Since the shape of the nanopores is critically important for their performance, in this work we focus on its analysis and study the dependence of the nanopore shape on the electron beam acceleration voltage. We show that the nanopore adopts a funnel-like shape, with a central pore penetrating the entire membrane, surrounded by an extended shallow-etched region at the top of the membrane. While the internal nanopore size was found to depend on the electron acceleration voltage, the nanopore edges extended beyond the primary electron beam spot size due to long-range effects, such as radiolysis and diffusion. Moreover, the size of the peripheral-etched region was found to be less dependent on the acceleration voltage. We also found that chemical etching is the rate-limiting step of the process and is only slightly dependent on the acceleration voltage. Furthermore, due to the chemical etch process the chemical composition of the nanopore rims was found to maintain the bulk membrane composition.

Advances in gas-mediated electron beam-induced etching and related material processing techniques

“…3(a-h)). Sample applications include iterative editing of individual nanostructures [85,19], repair of photolithographic masks [27,28], fabrication of nanopores in membranes [30,35], etching of 3D in-plane features in photoresist [37], and re-shaping of tips used in scanning probe microscopy [33,38]. EBIE has also been used to improve the purity of materials grown by EBID.…”

“…The technique is analogous to focused ion beam processing [6][7][8][9][10][11], but avoids damage, staining and redeposition artifacts caused by ion bombardment. EBIE is realized using gaseous precursors such as H 2 O, O 2 , NH 3 , XeF 2 , Cl 2 and SF 6 , which have been used to volatilize a wide range of materials, including graphene [12], single [13] and multi-walled [14] C nanotubes, amorphous carbon [15][16][17][18], single crystal [19][20][21][22] and nano-crystalline [23] diamond, Si, SiO 2 , Si 3 N 4 , Cr, Ti, TaN and photoresist [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38]. Historical overviews and reviews of the EBIE technique and the underlying chemical pathways can be found in references [1][2][3][4][5].…”

Fabrication of Solid State Nanopore in Thin Silicon Membrane Using Low Cost Multistep Chemical Etching

“…Recent advancements in nanofabrication techniques allow artificial solid-state nanopores to be fabricated in Si 3 N 4 , SiO 2 , Si, and alumina [2,6,12,13,14,15,16,17,18,19,20,21,22,23,24,25]. These nanopore devices uncover many advantages, such as the ability to control a pore diameter, increased mechanical strength, and integration with micro/nano-devices.…”

“…To date, inductively-coupled plasma (ICP)-enhanced reactive ion etching (RIE) [13,17,21,22], focused ion beam (FIB) micromachining via transmission electron microscopy (TEM) technology [6,13,14,17,20,22,25], and electron beam lithography [2,12,18,20] have been used frequently to pattern micro and nanopores directly on the substrate after some modification. Despite the availability of large varieties in pore fabrication techniques, it is still very desirable to develop simpler and faster methods without using the above mentioned high energy electron beam techniques.…”

“…A uniform pore size of approximately 1–2 µm in Si (p-type) with resistivity of 9–13 Ω·cm and 15.5 µm pore size in Si (n-type) with resistivity of 20 Ω·cm were produced by adding ACN and CTAC in an aqueous electrolyte, respectively [30,31]. To conclude, pores fabricated using DMF [22], CAN [23], and CTAC [24] are not etched all the way down even after increasing the current density from 3.5 to 15.5 mA/cm 2 . Moreover, their porous structures are not compatible with any biological sensing applications.…”