Low resistivity copper germanide on (100) Si for contacts and interconnections

We have deposited thin films of Cu₃Ge on (100) Si by the sequential e-beam deposition of an amorphous Ge layer followed by a polycrystalline Cu layer. The films were then annealed in flowing N₂ for 30 min over a temperature range of 150-600°C to induce complete recrystallization of the Cu-Ge films. Films of Cu₃Ge form a smooth, atomically sharp interface with (100) Si over a wide range of anneal temperatures, as determined by transmission electron microscopy, indicating the lack of any chemical reactions, i.e., compound formation, at the film/substrate interface. We have observed by secondary ion mass spectrometry, that a substantial amount of Si has diffused into the Cu-Ge in varying amounts that exhibit strong dependence on the anneal temperature. Despite the large amount of Si that has diffused into the films, the Cu₃Ge maintains its low resistivity (ρ=10-15 μΩ cm) up to an anneal temperature of 600°C, at which point the film completely loses its structural integrity, i.e., it becomes discontinuous with the formation of complex compounds. These results show that Cu₃Ge represents a potential candidate material for contact and metallization for next generation Si-based semiconductor devices.