HfC Sputtering parameters optimization and film characterization

Hafnium Carbide (HfC) is a refractory ceramic known for its exceptional properties, making it suitable for a wide range of applications. This project investigates the potential utilization of HfC in Micro or Nano Electromechanical Systems (MEMS/NEMS) and explores the effects of physical vapor deposition (PVD) parameters on film stress and resistivity. The study uses RF and DC sputtering with different sputtering powers, pressures and bias power. Experimental results demonstrate a linear relationship between deposition rates and sputtering power. In RF, compressive stresses increase linearly with sputtering power for bias powers of 0W and 15W, while a minimum stress is observed at a sputtering power of 200W (3.8GPa) with a bias power of 30W. Introducing bias power significantly reduces film stress, with an average reduction of 45% for 30W bias compared to cases without bias. On the other hand, resistivity of the films displays a non-linear dependence on sputtering power. For 30W bias, resistivity initially increases and then decreased with increasing sputtering power. In DC-sputtered HfC films, while compressive stress decreases with pressure following a power law, resistivity increases exponentially. Resistivity also decreases exponentially with power. Increasing the sputtering power proved to be essential in achieving low resistivity and stress. Notably, the best results are obtained with 300W sputtering power at 0.015 mbar, yielding a low stress of 251 MPa and a resistivity of 0.41 mΩ · cm. Additionally the optical constants n and k have been determined for RF and DC recipes through ellipsometry. The RF results could resemble to what is found in recent literature, albeit the constants measured for DC present a different behavior, meaning that more trials are needed for certainty.