Thermal stability and electrical properties of pulsed laser-deposited Hf-silicate thin films for high-k gate dielectric applications

Hf-silicate films were deposited directly onto n-type Si (100) substrates and Pt-coated Si substrates by a pulsed laser deposition technique using a ceramic Hf-silicate target. The thermal stability and electrical properties of Hf-silicate films have been investigated by x-ray diffraction, differential thermal analysis, atom force microscopy, x-ray photoelectron spectroscopy, capacitance–voltage (C–V) and leakage current–voltage (I–V) measurements. The amorphous structure of Hf-silicate films was found to be stable up to at least 900°C. A crystallization transformation from the amorphous phase to a polycrystalline tetragonal structure occurs under rapid thermal annealing for 3 min at 1000°C. The amorphous Hf-silicate film exhibits a high dielectric constant of about 14.1 measured in a Pt/Hf-silicate/Pt capacitor structure. The smoothness and electrical properties of films have been improved by rapid thermal annealing in N₂ ambient at 900°C for 30 s. A very small equivalent oxide thickness of 0.95 nm for 2.6 nm Hf-silicate film on the n-Si substrate and a low leakage current of 24 mA cm⁻² at 1 V gate voltage were obtained. Thus, Hf-silicate films with good thermal stability can be one of the most promising candidates for future high-k gate dielectric applications.