Electrical study of Al/HfO₂/p-Si (100) gate stack

Low leakage current density and high relative permittivity (dielectric constant) are the key factors in order to replace the SiO₂ from Si based technology towards its further down scaling. HfO₂ thin films received significant attention due to its excellent optoelectronic properties. In this work, ultra – thin (17 nm) HfO₂ films on Si substrate are fabricated by RF sputtering. As deposited films are amorphous in nature and in order to get the reasonable high dielectric constant the films are annealed (700°C, 30 min) in nitrogen environment. A high refractive index (2.08) and small grain size (~10) nm was extracted from ellipsometry and XRD, respectively. The AFM study revealed a small RMS surface roughness 9 Å. Towards electrical exploration, the films are integrated in Metal – Insulator – Semiconductor (MIS) capacitors structure. The oxide capacitance (C_ox), flat band capacitance (C_FB), flat band voltage (V_FB), and oxide trapped charges (Q_ot) calculated from high frequency (1 MHz) C-V curve are 490 pF, 183 pF, 1.33 V and 1.61x10⁻¹⁰ C, respectively. The dielectric constant calculated from accumulation capacitance is 17. The films show a very low leakage current density 4.3×10⁻⁸ A/cm² at ±1 V.