Applied Physics

Copper Confinement

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Science  22 Dec 2006:
Vol. 314, Issue 5807, pp. 1842-1843
DOI: 10.1126/science.314.5807.1842d

As microelectronic circuitry continues to shrink, and devices are packed onto chips at increasingly higher densities, two main concerns must be addressed: heat dissipation and interconnection reliability. Copper has therefore begun to replace aluminum as the metal of choice for on-chip wiring, on account of both its lower resistivity (which reduces heat generation) and its resistance to electromigration. However, Cu tends to diffuse rapidly into silicon, generating electronic traps within the Si bandgap that are detrimental to device performance. To address this shortcoming, the use of diffusion barriers between Si and Cu is being explored. The materials composing such barriers must be compatible with the fabrication process and also resistant to recrystallization during the high-temperature processing steps, a typical cause of failure. Hafnium nitride (HfNx), with a melting temperature exceeding 3300°C, has attracted strong interest in this vein. Rawal et al. have investigated the combined use of thin layers of Ge/HfNx as a diffusion barrier. They find that the bilayer system is more effective than a single HfNx barrier layer, a result that they attribute to the ready reaction of Ge with Cu to form Cu3Ge, thereby immobilizing much of the Cu that could otherwise diffuse through the HfNx layer. — ISO

Appl. Phys. Lett. 89, 231914 (2006).

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