Structural, mechanical, and electrical properties of magnetron-sputtered HfO2/SiO2 stacks

We systematically investigate the influence of sputtering pressure and film thickness on the structural, mechanical, optical, and electrical properties of magnetron-sputtered HfO2 layers for ion-sensitive field-effect transistor applications. Unlike extensively studied atomic layer deposited films, sputtered HfO2 remains less characterized, particularly regarding its suitability for sensor applications. Structural analysis reveals that partial crystallization of HfO2 can occur during nominal room-temperature deposition, with higher sputtering pressures promoting the formation of monoclinic phase. The as-deposited films exhibit compressive stress that increases strongly with thickness, reaching about −1500 MPa for 193 nm thick films, whereas after annealing at 950 °C, the stress becomes tensile. Electrical characterization of Al/HfO2/SiO2/Si capacitors reveals that the density of fixed charges ranges from −6.6 × 1010 cm−2 to approximately zero, depending on HfO2 thickness, with thinner films exhibiting higher negative fixed charge density localized at the HfO2/SiO2 interface. The interface state density, determined from conductance-voltage measurements, increases with HfO2 thickness from below 5 × 1010 cm−2 eV−1 for films thinner than 70 nm to approximately 8 × 1012 cm−2 eV−1 for 193 nm thick films. The correlation between microstructure, stress, and electrical properties provides practical guidelines for optimizing sputtered HfO2/SiO2 stacks for electronic and sensor applications.