The controlled fabrication of nanopores by focused electron-beam-induced etching

Abstract

The fabrication of nanometric holes within thin silicon-based membranes is of great importance for various nanotechnology applications. The preparation of such holes with accurate control over their size and shape is, thus, gaining a lot of interest. In this work we demonstrate the use of a focused electron-beam-induced etching (FEBIE) process as a promising tool for the fabrication of such nanopores in silicon nitride membranes and study the process parameters. The reduction of silicon nitride by the electron beam followed by chemical etching of the residual elemental silicon results in a linear dependence of pore diameter on electron beam exposure time, enabling accurate control of nanopore size in the range of 17-200 nm in diameter. An optimal pressure of 5.3 x 10(-6) Torr for the production of smaller pores with faster process rates, as a result of mass transport effects, was found. The pore formation process is also shown to be dependent on the details of the pulsed process cycle, which control the rate of the pore extension, and its minimal and maximal size. Our results suggest that the FEBIE process may play a key role in the fabrication of nanopores for future devices both in sensing and nano-electronics applications.

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

“…Hence, σ is an 'effective' [23] cross-section for fragment generation. However, in some cases, such as XeF 2 EBIE of SiO 2 [26] and XeF 2 EBIE of Si 3 N 4 [30], etching has been argued to proceed through a cyclic process of electron induced removal of O (or N) from the substrate surface, and spontaneous etching of excess Si by XeF 2 . Such processes can be modeled by the above equations provided that σ is taken to represent a cross-section for the electron induced restructuring step that leads to the removal of O (or N) from the surface.…”

“…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 nanopores in multi-layered silicon-based membranes using focused electron beam induced etching with XeF2 gas

“…Samples pre-cleaned by UV-Ozone treatment were exposed to 1 ms electron beam pulses at a rate of 500 Hz at a fixed location on the surface. An electron acceleration voltage of 20 kVand a beam current of~0.44 nA were used in order to achieve maximal lateral resolution [29,30]. In each experiment, an array was fabricated with the total electron beam exposure time varying in the range of 0.1 to 24 s for each nanopore element in the array, by varying the number of pulses used in the process.…”

“…In this process, chemical etching is locally accelerated by exposure to a low energy focused electron beam [29,30]. The formation of nanopores with diameters down to 20 nm in silicon nitride membranes was achieved by localized reduction of the nitride by the electron beam, followed by etching of the silicon reduction product by the introduction of XeF 2 vapor in-situ.…”