Characterization of TiHfN ternary alloy films as a barrier between Cu plug and Si

A TiHfN ternary alloy film is examined as a candidate reliable barrier to replace W with Cu in contact plug with Si. A low-resistivity Ti12Hf32N56 film (~120 µΩ cm) is successfully obtained by reactive sputtering. The phase stability of the compound with a N-rich composition is observed. This is because both TiN and HfN, the constituents of this compound, have stable phases with N-rich composition and the same crystalline structure, and the TiHfN compound is considered as an alloy of these constituents. The Cu/Si contact model with a 10-nm-thick TiHfN barrier of nanocrystalline texture showed excellent barrier properties with negligible structural changes owing to annealing for 1 h at 500 °C or higher. The excellent barrier properties and low resistivity obtained are attributed to the structure of the alloy film, in which the alloy has a NaCl structure with Ti and Hf atoms randomly substituted at cation sites.