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

Abstract

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.