Thermal and plasma enhanced atomic layer deposition ruthenium and electrical characterization as a metal electrode

Ruthenium thin films were grown by thermal and plasma-enhanced atomic layer deposition (PE-ALD) using O2 and ammonia (NH3) plasma, respectively. RuCp2 and Ru(EtCp)2 were used as Ru precursors. Pure and low resistivity (<20 μΩ cm) Ru films were grown by PE-ALD as well as thermal ALD. PE-ALD Ru showed no nucleation delay on various substrates including TaNx, Si, and SiO2, in contrast to thermal ALD Ru. And the root-mean-square (RMS) roughness of PE-ALD Ru was lower than that of thermal ALD Ru. Additionally, metal–oxide–semiconductor (MOS) capacitor composed of p-Si/ALD Ta2O5/ALD Ru (35 nm) was fabricated and C–V measurements were performed for as-deposited sample. Very small hysteresis of 20 mV was obtained, and effective work function difference to Si substrate was minimal as −0.03 V. For comparison, MOS capacitor was fabricated using sputtered Ru and large hysteresis of 0.5 V and flat band voltage (VFB) shift to negative value were observed. This result indicates that ALD process produces more reliable, damage free Ru gate compared to sputtering process.