A newly developed strategy to solve electromigration could potentially extend the life and performance of devices based on nanoelectronics and semiconductors.

Researchers from the University of South Florida are behind the new materials science and nanotechnology breakthrough. The novel solution involves coating copper metal interconnects - small structures that connect components and circuits in ICs - with hexagonal boron nitride. The compound used is an atomically thin, 2D material that is also an insulator with a structure similar to graphene. A detailed report on the new electromigration mitigation strategy appears in the latest journal Advanced Electronic Materials, titled "Mitigation of Electromigration in Metal Interconnects via Hexagonal Boron Nitride as an Ångström-Thin Passivation Layer."

Failure Location Due to Electromigration, Captured Under an SEM
(Photo: Patrick-Emil Zörner via Wikimedia Commons)
Image of a failure location caused by electromigration in a copper conductor track under the scanning electron microscope. The passivation was previously removed by reactive ion etching (RIE) and hydrofluoric acid (HF). The etching processes have not been tried and tested and are based on attempts to achieve the best possible result.

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Overcoming Electromigration in Electronic Devices

Electromigration is a persisting problem in electronics, even in the micro and nanoscales. It is a phenomenon that occurs when an electrical current, passing through a conductive material, causes parts of the material to be transported along with it. Basically, the movement of current and charged particles also share momentum to the atoms of the conductor, causing it to move, according to IC design leader CadenceThis erosion of materials on the atomic scale eventually causes the device to fail. Additionally, the effects of electromigration basically grow more significant as the structure size of the material decreases, making it a critical concern in the field of nanoelectronics, where the precise volume of molecules determines the material's performance.

Conventional methods of limiting electromigration in semiconductors include the use of a barrier or liner material. However, installing a dedicated material for this purpose takes up additional space on the wafer that could've been used for additional transistors or another component, effectively affecting the transistor density and computing power in ICs. While the new effort, led by mechanical engineering assistant professor Michael Cai Wang, builds on the same concept, they use the thinnest available materials: 2D materials that are only a few atoms thick.

"This work introduces new opportunities for research into the interfacial interactions between metals and ångström-scale 2-D materials. Improving electronic and semiconductor device performance is just one result of this research," Wang said in a USF news release. He adds that their findings could help advance the future of semiconductors and IC manufacturing. With their new encapsulation strategy that uses hexagonal boron nitride allows device density and Moore's Law to be extended more. The ångström-scale where the new technology operates is about a tenth of a nanometer, and a nanometer is basically 1/60,000 of the average thickness of a human hair.

Better Performance, Longer Life for Nanoelectronics, Semiconductors

Researchers created their copper interconnects coated with a monolayer of the atomically thin hexagonal boron nitride by using a back-end-of-line compatible method. It resulted in a 2500 percent increase in the device lifetime and a 20 percent increase in its higher current devices compared with similar devices without the 2D coating.

Additionally, the thinness of the coating material frees up space in the microchip, which could increase IC component densities in the future. Basically, the novel electromigration mitigation strategy improves device efficiency and decreases energy consumption, in addition to the possibilities of ushering the next generation of more powerful devices.


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