Physical and electrical properties of ultrathin $HfO2/HfSixOy$ stacked gate dielectrics on compressively strained-$Si0.74Ge0.26/Si$ heterolayers

The physical properties of $HfO2/HfSixOy$ stacked gate dielectric films deposited on compressively strained-$Si0.74Ge0.26/Si$ heterolayers have been investigated using Rutherford backscattering spectrometry, high-resolution transmission electron microscopy, time-of-flight secondary ion mass spectroscopy, and Auger electron spectroscopy measurements. Polycrystalline $HfO2$ film with physical thickness of ∼4.0 nm and an amorphous interfacial layer with a physical thickness of ∼4.5 nm has been observed. Secondary ion mass spectroscopy and Auger electron spectroscopy analyses show the formation of an amorphous Hf-silicate interfacial layer between the oxide deposited and SiGe films. The electrical properties in terms of capacitance–voltage $(C–V),$ conductance–voltage, hysteresis, current density-electric field, and shift in gate voltage under constant current stress have been studied using a metal–oxide–semiconductor structure. Dielectric constants of 26 for $HfO2$ and 8.0 for the interfacial Hf-silicate layer have been calculated from the high frequency $C–V$ (100 kHz) characteristics. These dielectrics show an equivalent oxide thickness as small as 0.6 nm for $HfO2$ and 2.2 nm for the interfacial silicate layer. The fixed oxide charge density and interface state density are found to be $1.5×1012 cm−2$ and $5.5×1011 cm−2 eV−1,$ respectively, for $HfO2$ with the interfacial layer and those values are found to be $3.5×1012 cm−2$ and $1.3×1012 cm−2 eV−1$ for the Hf-silicate interfacial layer, respectively. The metal–oxide–semiconductor capacitor shows low hysteresis of 0.08 V, low leakage current density of $∼10−7 A/cm2$ at −1.0 V, and breakdown field of 6.5 MV/cm for $HfO2$ with interfacial layer. Significant improvement of the charge trapping properties under Fowler–Nordheim constant current stress in $HfO2$ with the interfacial layer has been observed.