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

Hf–aluminate (Hf–Al–O) films have been deposited directly on n-type Si (100) substrates and Pt-coated Si substrates using the pulsed laser deposition technique with a ceramic Hf–Al–O target, respectively. The structure and electrical properties of Hf–Al–O films have been investigated by x-ray diffraction, differential thermal analysis, x-ray photoelectron spectroscopy (XPS) and capacitance–voltage (C–V) and leakage current–voltage (J–V) measurements. The composition of films was determined as Hf1.00Al2.01O4.92, which is nearly the same as the HfO2 : Al2O3 composition from XPS detection. The amorphous structure of Hf–Al–O films remains stable up to 900°C. A crystallization transformation from an amorphous phase to a polycrystalline tetragonal structure occurs with rapid thermal annealing for 3 min at 1000°C. A thin interfacial layer in Hf–Al–O/n-Si was identified as a mixed compound of Hf–Al–Si–O. The amorphous Hf–Al–O film exhibits a high dielectric constant of about 16.6, determined by measuring a Pt/Hf–Al–O/Pt capacitor structure. A very small equivalent oxide thickness of 0.74 nm for a 3 nm Hf–Al–O film on an n-Si substrate and a leakage current of 0.17 A cm−2 at a 1 V gate voltage were obtained. Hf–aluminate films with high thermal stability and good electrical properties can be one of the most promising candidates for high-k gate dielectric applications.