Paper PS-WeM13
Direct Metal Nanowire Patterning Using Ion Beam Etch

Wednesday, November 1, 2017, 12:00 pm, Room 23

Scaling of metal lines to sub-10 nm dimensions is a pivotal driving force for progressing in the field of electronics and physics. Their fabrication by conventional lift-off/damascene approaches can be highly demanding. Some of the challenges which need to be circumvented for their creation are high resolution lithography of thinner resist and pattern transfer to form well-resolved lines/spaces. In addition, stress induced ruptures can form in the grain boundaries of the deposited metal film as the linewidth and grain size converge to similar dimensions. Here, we showcase an approach wherein we can directly pattern narrow metal lines with the use of relaxed dimension 248 nm optical lithography. Ru metal films of thicknesses ranging from 8-12 nm were deposited in a conformal way atop 300 nm wide (lines/spaces), ~7 µm long and 25 nm high patterned oxide (SiO₂) core. The oxide core height and the metal thickness can be varied to provide the flexibility of tuning the metal cross-sectional area. Ion beam etch (IBE) using Ar⁺ ions was carried out to remove the film from the top and adjacent trenches of the oxide core, leaving behind long, continuous Ru lines of cross-sectional area <100 nm² along the oxide sidewalls. IBE works under the principle of physical momentum transfer (binary collision process) from the incident ions to the metal atoms which causes their eventual ejection from the substrate. Hence, unlike chemical etch, the physical etch process is not impacted by the change in grain size and grain boundaries of the metal. The cross-sectional area of the nanowires and its profile could be improved by controlling the Ar⁺ ion accelerating voltage (50-400V) and time. TEM investigation revealed that the use of this ion bombardment based physical etch process didn’t have an adverse impact on the metal crystallinity.

The Ru lines were electrically examined to estimate their performance as interconnects for advanced technology nodes. The electrical resistance yield achieved was >70%, indicating this physical etch process to be a robust method for such scientific studies. The fabrication method is not complex, compatible with the current silicon-based technology and can be extended to patterning of different metals and their alloys such as Ir, Rh amongst others.

References:

[1] L. G. Wen et al., ACS Appl. Mater. Interfaces, 2016, 8, 26119.

[2] S. Yasin, D. G. Hasko, H. Ahmed, Appl. Phys. Lett. 2001, 78, 2760.