"Carbon In, Carbon Out: Resistance Drops 45%—A Counterintuitive Leap for 2 nm Semiconductor Wiring [Reading Science]"

GIST, Samsung Electronics SAIT, and MIT Achieve Sevenfold Increase in Ruthenium Grain Size and 99.3% Alignment
Proven Effective in Narrow and Deep 3D Structures... Published in the International Journal "Science"

By intentionally introducing carbon into semiconductor wiring and then removing it, electrical resistance was reduced by more than 45%. This counterintuitive approach—utilizing carbon, previously considered an impurity in metals, only during the period when grains are growing—has succeeded in enhancing the performance of next-generation 2-nanometer (nm, one billionth of a meter) semiconductor wiring.

On August 21, Gwangju Institute of Science and Technology (GIST) announced that Dr. Yongryun Jo of the Central Instrument Research Institute, in collaboration with researchers from Samsung Electronics SAIT (formerly Samsung Advanced Institute of Technology) and the Massachusetts Institute of Technology (MIT), had developed a technology that controls the grain size and orientation of ruthenium, a next-generation semiconductor wiring material, using trace amounts of carbon. The research results were published online in the international journal "Science" on August 13.

Growth of ruthenium (Ru) grains and crystallographic orientation alignment process induced by carbon promoter (C-promoter). Courtesy of the research team

As semiconductors become miniaturized below the 2 nm level, the metal wiring within chips has become extremely thin. The problem is that as the wiring narrows, the flow of electrons is disrupted, and resistance increases dramatically. Ruthenium has emerged as a promising next-generation wiring material to supplement conventional copper; however, it also faces the challenge of increased resistance as electrons scatter at the grain boundaries between numerous small crystals.

The research team's solution was unexpectedly "carbon." By adding a minute amount of carbon to ruthenium, allowing it to facilitate grain growth and alignment during heat treatment, and then removing the carbon once its role was finished, they achieved a breakthrough. This approach exploits carbon not as an additive that permanently modifies the characteristics of the thin film, but as a "temporary promoter" that acts only during crystal growth.

When 0.48% Carbon Was Added, Grain Size Increased Sevenfold

Experiments varying the amount of carbon showed that the most pronounced effect occurred when 0.48 atomic percent (at%) of carbon—equivalent to about 5 out of every 1,000 ruthenium atoms—was added. If too much carbon was added, it actually hindered the alignment of the grains.

The process by which carbon aids grain growth was also elucidated. When heat treatment begins, carbon atoms within ruthenium migrate to the "grain boundaries" where grains touch each other. Subsequently, as carbon escapes in a gaseous state, it creates temporary voids, or "free volumes," near the grain boundaries. These spaces allow ruthenium atoms and grain boundaries to move more easily, enabling small grains to merge and realign in similar directions as they increase in size.

Growth and alignment process of ruthenium (Ru) grains induced by carbon promotion and the results of applying a three-dimensional structure. Provided by the research team

The research team directly observed this process using real-time in situ heating transmission electron microscopy (TEM). They tracked, in real time, how the grains grew and realigned as the sample was heated within the microscope.

As a result, the average grain size of ruthenium thin films subjected to heat treatment at 450°C increased more than sevenfold, from about 13 nm to 91.7 nm. The degree of alignment (texture coefficient) indicating grains oriented in one direction reached as high as 99.3%.

These changes in crystal structure significantly improved electrical properties. In an 8 nm thick ruthenium thin film, resistivity was measured at 11.2 microohm-centimeters (μΩ·cm), which is 29.0% lower than ruthenium produced without carbon. In actual ultrafine wiring structures, wiring resistance decreased by 45.4%. The researchers explained that these results meet the electrical performance requirements for next-generation semiconductor wiring at the 2 nm linewidth level.

Effective Even in Narrow and Deep 3D Structures

The technique was proven effective not only in flat thin films but also in complex three-dimensional structures. The team coated ruthenium 12 nm thick into narrow, deep trenches with an aspect ratio of 33:1 (depth to width). As a result, coating uniformity reached 99.1% along the sidewalls and bottoms of the trenches, and the directional orientation of the ruthenium crystals was maintained even in these complex structures.

Research team photo. (From left) Dr. Yongchul Lim, Samsung Advanced Institute of Technology, Dr. Yunhoo Ha, Researcher Youngmin Lee, Dr. Yongryun Cho, Advanced Analysis Center, Central Research Facilities, GIST. Provided by GIST

This demonstrates the potential for applying this technology even as semiconductor structures become more intricate and three-dimensional. The researchers expect it can be used in next-generation ultrafine semiconductor wiring below the 2 nm level and in highly integrated three-dimensional semiconductor structures going forward.

The significance of the research lies not in carbon itself, but in proposing a new material design strategy: instead of regarding trace elements in metals as impurities that must be removed or as additives to be retained in the final material, they can be employed as "temporary promoters" that disappear after facilitating the desired crystal structure.

Dr. Jo stated, "We demonstrated that trace elements in metals can be used not just as impurities that need to be removed, but as temporary promoters that enable grain migration and alignment before departing. This presents a new design principle for simultaneously controlling the structure and electrical performance of next-generation semiconductor wiring materials."

This content was produced with the assistance of AI translation services.