Ultra-fast direct growth of metallic micro- and nano-structures by focused ion beam irradiation

Abstract

An ultra-fast method to directly grow metallic micro- and nano-structures is introduced. It relies on a Focused Ion Beam (FIB) and a condensed layer of suitable precursor material formed on the substrate under cryogenic conditions. The technique implies cooling the substrate below the condensation temperature of the gaseous precursor material, subsequently irradiating with ions according to the wanted pattern, and posteriorly heating the substrate above the condensation temperature. Here, using W(CO)6 as the precursor material, a Ga+ FIB, and a substrate temperature of −100 °C, W-C metallic layers and nanowires with resolution down to 38 nm have been grown by Cryogenic Focused Ion Beam Induced Deposition (Cryo-FIBID). The most important advantages of Cryo-FIBID are the fast growth rate (about 600 times higher than conventional FIBID with the precursor material in gas phase) and the low ion irradiation dose required (∼50 μC/cm2), which gives rise to very low Ga concentrations in the grown material and in the substrate (≤0.2%). Electrical measurements indicate that W-C layers and nanowires grown by Cryo-FIBID exhibit metallic resistivity. These features pave the way for the use of Cryo-FIBID in various applications in micro- and nano-lithography such as circuit editing, photomask repair, hard masks, and the growth of nanowires and contacts. As a proof of concept, we show the use of Cryo-FIBID to grow metallic contacts on a Pt-C nanowire and investigate its transport properties. The contacts have been grown in less than one minute, which is considerably faster than the time needed to grow the same contacts with conventional FIBID, around 10 hours.

Comparison between Focused Electron/Ion Beam-Induced Deposition at Room Temperature and under Cryogenic Conditions

“…In the current work, the simulated tungsten concentration of about 8% at a fluence of 4 × 10 14 ions/cm 2 ( Figure 5), which is in the range of the optimized irradiation dose according to Córdoba et al [55], is also lower than the experimental surface concentration of above 20%, which gives an indication that diffusion processes and/or outgassing after the dissociation of the precursor molecules play a role but are not accounted for in the modelling. Although the W surface concentration starts to increase in the simulations with a fluence of 4 × 10 14 ions/cm 2 (Figure 5b), the tungsten surface concentration only starts to be significantly above the initial concentration of the precursor film for fluences above 10 16 ions/cm 2 (see Figure A1 in Appendix A).…”

“…However, no particular application was discussed or targeted. [55]. As shown in Figure 4, such working conditions plus ion doses in the range of 50 μC/cm 2 have been found favorable for obtaining homogeneous void-free W-C deposits.…”

“…The first example of direct growth of a nanopatterned material by cryogenic focused beam-induced deposition techniques was reported by Bresin et al using the (CH 3 ) 3 Pt(C p CH 3 ) precursor and electron irradiation, known as Cryo-FEBID [53,54]. The second example was reported by Córdoba et al using the W(CO) 6 precursor and ion irradiation, known as Cryo-FIBID [55]. Figure 2 illustrates the steps involved in such a process.…”

“…Córdoba et al have recently used 30-nm thick layers of W(CO) 6 precursor condensed at −100 • C, with focused Ga + ion irradiation under 30 kV beam energy and 10 pA beam current [55]. As shown in Figure 4, such working conditions plus ion doses in the range of 50 µC/cm 2 have been found favorable for obtaining homogeneous void-free W-C deposits.…”

Additive Nano-Lithography with Focused Soft X-rays: Basics, Challenges, and Opportunities

“…Several recent studies have demonstrated that focused electron beam induced processing (FEBIP) has high potential for the controlled bottom-up fabrication of metallic 3D nanostructures [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Furthermore, the basic processes during FEBIP are understood to more and more detail leading to developments towards more diverse, cleaner and more defined deposits for various potential applications [7,[15][16][17][18].…”