Nitric acid acs plus

Nanocomposite surfaces were prepared from materials supplied by Versum Materials, LLC (Tempe, AZ, USA). The original materials were made using industrial-scale advanced integrated circuit fabrication techniques, which include copper and tantalum chemical-mechanical polishing (CMP) and damascene integration on 200 mm silicon substrates [33 ,34 ,35 ] (Figure 1). Briefly, parallel-line comb structure patterns were transferred to the silicon oxide-coated substrate using lithography and dry-etching methods [33 ,34 ,36 ]. A thin tantalum seed layer and copper were deposited on the patterned structures. CMP [37 ,38 ] was used to remove excess copper and tantalum. Polishing continued until the silicon oxide lines were exposed as shown in Figure 1c. In-house, additional copper was removed by chemical stripping with ~9.4 M diluted nitric acid ACS Plus (Fisherbrand^®, Fisher Scientific International Inc., Pittsburgh, PA, USA) for ~45 min. The final rinse consisted of deionized water and anhydrous ethanol. The finished device consisted of a parallel-line comb structure with trench sidewalls and bottom surfaces coated with a thin layer of tantalum, while the top surfaces of the lines contained exposed silicon oxide (Figure 1d).

Nano- to micron-scale parallel line/trench comb structures were fabricated on 200 mm silicon substrates using high-precision advanced integrated circuit fabrication techniques and damascene integration methods [55 ,56 ,57 ]. These structures contained 0.18, 0.25, 0.5, 2, and 50 μm equal width trenches and lines. Samples were provided by Versum Materials, LLC (Tempe, AZ, USA). Photolithography and dry etching techniques [55 ,56 ,58 ] were used to transfer comb structure patterns to the silicon oxide coated substrate. Specimens were then coated with a thin layer of tantalum seed and copper. Excess copper was removed using a copper chemical-mechanical polishing technique [59 ,60 ]. Any remaining copper was chemically stripped with ~9.4 M diluted nitric acid ACS Plus (Fisherbrand®, Fisher Scientific International Inc., Pittsburgh, PA, USA) for ~45 min. Specimens were rinsed with deionized water and anhydrous ethanol prior to use. The final surface consisted of parallel trench structures that were conformably coated with ~20 nm of tantalum. The trench depth was ~700 nm. Representative SEM micrographs of the test structures are shown in Figure S1.

Tantalum thin film-coated comb structure specimens were fabricated using an advanced integrated circuit back-end-of-line processing method on 200-mm silicon wafers [58 ,59 ,60 ]. They were supplied by Versum Materials, LLC (Tempe, AZ, USA). The fabrication steps for these silicon-based devices are briefly summarized and illustrated in Figure 1. Parallel line comb structures with equal-width trenches (T) and lines (L) were transferred to the silicon oxide films deposited on the silicon substrate using lithography and dry etching techniques [58 ,59 ,60 ,61 ]. The rectangular-shaped comb structure areas were no smaller than 1.8 mm² with widths larger than 1 mm. The tantalum seed layer and copper were deposited on these patterned surfaces, and excess copper was removed using chemical mechanical polish methods [61 ,62 ,63 ]. The remaining copper was stripped by submerging the specimens in ~9.4 M nitric acid for ~45 min followed by rinsing with deionized water and ethanol. This acid-stripping agent was a diluted solution from 70% nitric acid ACS Plus (Fisherbrand®, Fisher Scientific International Inc., Pittsburgh, PA, USA). The line and trench dimensions fabricated are summarized in Table 2. The trench depths (D) of all patterned comb structures were fixed at ~700 nm.