Ru and RuO₂ gate electrodes for advanced CMOS technology

Due to the downscaling of device dimensions in CMOS technology, the introduction of metal gate electrodes and high-k dielectrics will be necessary in order to meet future performance requirements. In particular, deposition techniques such as chemical vapor deposition (CVD) and molecular beam epitaxy (MBE) have been identified as promising methods for growth of these materials. In this scope, we have analysed properties of Ru and RuO₂ gate electrodes in metal-oxide-semiconductor (MOS) gate stacks prepared on SiO ₂, atomic-layer chemical vapor deposition (ALCVD) Al ₂O₃ and MBE Y₂O₃ dielectric films. The Ru and RuO₂ films were grown by metal-organic chemical vapor deposition (MOCVD) at 250°C. The dielectric and metal gate electrode films were analysed by X-ray diffraction and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). The resistivity of the films at room temperature were 20 and 150μΩcm for the Ru and RuO₂ films, respectively. Thermal stability of the films in forming gas (10% H₂ + 90% N ₂), nitrogen and oxygen environments was investigated by applying low temperature (420°C, 30min) and rapid thermal (800°C) annealing. The results indicate good thermal behavior of the Ru films but limited thermal stability of the RuO₂ films. The Ru and RuO₂ gate electrode workfunctions were extracted from high-frequency capacitance-voltage measurements on MOS capacitors. The obtained results are discussed in connection with applications of Ru and RuO₂ films as gate electrodes in CMOS technology.