Epitaxial Metals for Interconnects Beyond Cu: Resistivity, Reliability

As the critical dimensions of interconnects are scaled towards and then below the mean free path of Cu (39 nm at room temperature), the resistivity is found to increase. The increase in resistivity, termed the resistivity size-effect, results in resistance increases beyond Ohm's law of dimensional scaling and leads to large power consumption and limits improvements in computing performance.The resistivity size-effect in Cu is the result of electron scattering at grain boundaries and surfaces. Thus, for interconnects beyond Cu, epitaxial single crystal metals, absent of grain boundaries, have been investigated. Electrochemical deposition of epitaxial Co on an epitaxial Ru seed layer has provided proof-of-principle demonstration of room temperature deposition for potential implementation in BEOL technology. An electron transport model based on a tight-binding (TB) approach has been used to compute the conductivity of Ru lines. The TB based approach allows conductivity of structures comprising large ensembles of atoms (10⁵-10⁶) to be computed.