Size effect on the mechanical behaviour of polycrystalline copper microbeams

Abstract

To reduce costs and to remain competitive in the worldwide electronics industry, semiconductor manufacturers continually miniaturize devices. Today, the interconnect lines linking electronic components have diameters of the order of 100 nm or smaller. At the nanometre scale, strong size effects modify the mechanical properties of materials. To examine such effects, freestanding microbeams with geometrical and microstructural properties similar to those of interconnect lines have been designed. The yield stress dependence of the microbeams on their microstructure, shape and dimensions was investigated. As predicted by the Hall–Petch law, an increase in the yield stress with a decrease in the grain size was observed. In addition, a decrease in the cross-section of the microbeams at a fixed grain size led to a decrease in the yield stress. Hence, the yield domain of interconnect lines was observed to be controlled by two competitive size effects. This result imposes some restrictions on the design of electronic devices.

Keywords:

• size effect
• Hall–Petch
• nanostructure
• copper
• semiconductor

Acknowledgements

The support of Altis Semiconductor and Elastic GB [grant number ANR-09-BLAN-0079] for this research project is acknowledged. The authors gratefully acknowledge Ladisla Kubin and Olek Maciejak for their helpful discussions. The authors are also grateful to Pierre Vekeman, Daniel Bertrand and Pascal Deconinck from Altis Semiconductor for their support and technical assistance.