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Maroudas Team Discovers New Method to Reduce Surface Roughness in Conducting Thin Films

Roughness Reduction Sequence

Roughness Reduction Sequence

A team of researchers from UMass Amherst headed by Professor Dimitrios Maroudas of the Chemical Engineering (ChE) Department has found a way to reduce the surface roughness of conducting thin films used in microelectronics, potentially boosting their ability to conduct electrical and thermal energy. According to a press release by the American Institute of Physics (AIP), surface roughness reduction is “a really big deal when it comes to fundamental surface physics and while fabricating electronic and optical devices.”

The findings of the Maroudas team were published recently in Applied Physics Letters, an AIP journal, in an article written by Maroudas and Lin Du of our ChE department. See media coverage: Phys.org, ScienceDaily, AIP Publishing, EurekAlert!, AAAS, Alphagalileo, Nanowerk, ECN magazine, ScienceNewsline, AZOMaterials, Newswise, LongRoom, Parallelstate, NewsLocker, IDTechEx, naijasoiety, Opennano, Topix, Hitechdays.

 The article was also an Applied Physics Letters Editor’s pick for the week of March 6, 2017.

“In a significant advance,” AIP summarized the significance of the research, “particularly within the microelectronics realm, engineers have established electrical surface treatment of conducting thin films as a physical processing method to reduce surface roughness.”

The AIP piece explained that, as transistor dimensions within integrated circuits continue to shrink, smooth metallic lines are required to interconnect these devices. “If the surfaces of these tiny metal lines aren't smooth enough, it substantially reduces their ability to conduct electrical and thermal energy -- decreasing functionality.”

“We've been thinking hard about this roughness problem for many years, since showing that electric currents can be used to inhibit surface cracking,” said Maroudas in the AIP press release. “So as soon as we developed the computational tools to attack the full film roughness problem, we got to work.”
The team’s research focused on using a copper film on a silicon nitride layer in order to quantify the model parameters for their simulations and compare them with existing experimental findings, which the researchers were able to reproduce.

"Surface electromigration is the key physical concept involved," Maroudas explained in his AIP interview. "It's the directed transport of atoms on the metal surface due to the so-called electron wind force, which expresses the transfer of momentum from the electrons of the metal moving under the action of an electric field to the atoms (ions) -- biasing atomic migration."

Maroudas compared this process to the diffusion of ink in flowing water.

“Electromigration's role in the transport of surface atoms is analogous to that of convection due to flow on the transport of ink within the water,” said Maroudas. “The combined effects of a well-controlled applied electric field and rough surface geometry drive the atoms on the metal surface to move from the hills of the rough surface morphology to the neighboring valleys, which eventually smooth away the rough surfaces.” (March 2017)

Detailed caption for above image: "Sequence of snapshots from a computer simulation of electric-field-driven surface morphological evolution of a copper thin film, demonstrating current-induced surface smoothening."