Carbon cuts ruthenium wiring resistance 45.4% in lab

Dr. Jo Yung-ryun of the Advanced Analysis Center at the Central Research Facilities of the Gwangju Institute of Science and Technology examined the atomic arrangement inside a ruthenium thin film using a transmission electron microscope. After the South Korean-American research team added a small amount of carbon and applied heat treatment, ultrafine wiring resistance fell 45.4% versus ruthenium without carbon. The research was conducted jointly by researchers from Samsung Electronics SAIT and the Massachusetts Institute of Technology and was published in the journal Science.

Ruthenium is a candidate material that could address copper’s electrical limitations as wiring widths narrow to several nanometers. The problem is the grain boundaries that form inside thin metal films. When electrons scatter at these boundaries, where small crystals meet, wiring resistance increases. Existing methods for controlling crystal orientation require substrates with well-matched crystal structures or high-temperature heat-treatment conditions, limiting their use in actual semiconductor processes.

The researchers used carbon not as an impurity to be removed but as a temporary helper. Adding 0.48 at% carbon—about 5 of every 1000 ruthenium atoms—most effectively promoted grain growth and orientation during heat treatment; excessive carbon instead interfered with alignment. In-situ heating transmission electron microscopy showed that after treatment at 450°C, the average grain size grew from about 13 nm to 91.7 nm, while the degree of crystallographic orientation reached 99.3%.

The electrical results showed a similar improvement. The resistivity of an 8 nm-thick ruthenium thin film was measured at 11.2 μΩ·cm, 29.0% lower than that of a film without the carbon promoter. The team also confirmed reduced resistance in an ultrafine wiring structure with a linewidth of about 2 nm, saying it met the electrical performance required for next-generation wiring.

The result expands the design options for next-generation chip wiring. Metal crystals can be oriented even on amorphous insulating substrates, and the researchers confirmed potential applications in complex three-dimensional semiconductor structures and 3D memory. However, the findings are currently limited to the joint team’s experimental results. They do not demonstrate performance or yield in mass-production processes or actual products, and the technology remains at the laboratory research stage.