Plasma-Enhanced ALD of HfOx for Effective Surface Passivation of Silicon: A Material and Interface Study

This study investigates the silicon surface passivation characteristics of hafnium oxide (HfOₓ) thin films deposited using plasma-enhanced atomic layer deposition (PEALD), with a particular focus on remote plasma power ( P _w ) induced growth mechanism of the films. The HfOₓ films were grown on Si (100) wafers at a substrate temperature of 200°C using tetrakis(ethyl-methyl-amino)hafnium (TEMAHf) as the metal precursor and oxygen plasma as the oxidant. Structural analysis performed using grazing incidence X-ray diffraction (GIXRD) confirmed the amorphous nature of all the films, while atomic force microscopy (AFM) revealed smooth surfaces with roughness < 0.2 nm. The variation of films thickness, as evaluated using, spectroscopic ellipsometry showed that growth per cycle (GPC) varied with plasma power. XPS analysis revealed that plasma power of 2500 W effectively suppressed oxygen-related defect states in the HfOₓ films. A maximum effective minority carrier lifetime ( τ _eff ) of 390 µs, corresponding to a surface recombination velocity (SRV) < 50 cm/s was achieved for the films with a thickness of 16 nm, deposited at a P _w of 2500 W. Plasma induced modifications on silicon surface were studied using electrical characterization of its MOS capacitors and the results indicate that chemical passivation at the Si/HfOₓ interface played a dominant role in reducing the interface trap density ( D _it ). These results emphasise the critical role of plasma power in optimizing the growth dynamics and passivation performance of PEALD-grown HfOₓ films for advanced silicon-based devices.