Structural and electrical characteristics of the interfacial layer of ultrathin ZrO2 films on partially strain compensated Si0.69Ge0.3C0.01 layers

Abstract

The structural characteristics of ZrO2 films along with the interfacial layers deposited on partially strain compensated Si0.69Ge0.3C0.01/Si heterostructure have been investigated using x-ray diffraction (XRD), high resolution transmission electron microscopy (TEM), time-of-flight secondary ion mass spectroscopy (SIMS), and x-ray photoelectron spectroscopy (XPS) measurements. XRD spectra show the films to be polycrystalline with both monoclinic and tetragonal phases. The ZrO2 film with physical thickness of ∼8.5 nm and an amorphous interfacial layer with a physical thickness of ∼3.6 nm have been observed by high resolution TEM, SIMS and XPS. SIMS and XPS analyses show the formation of an amorphous Zr–germano–silicate interfacial layer between the deposited oxide and SiGeC films. The electrical properties in terms of capacitance–voltage (C–V), conductance–voltage, current density–voltage, and gate voltage shift (ΔVg) under a constant current stressing have been studied using a metal–insulator–semiconductor (MIS) structure. A dielectric constant of 17.5 for ZrO2 and 7.0 for interfacial Zr–Ge–silicate layer have been calculated from the high frequency C–V characteristics. These dielectrics show an equivalent oxide thickness (EOT) as low as 1.9 nm for ZrO2 and 2.0 nm for the interfacial silicate layer. The MIS capacitor shows an extremely low leakage current density of ∼9×10−8 A/cm2 at a gate voltage of −1.0 V, breakdown field of 7 MV/cm based on EOT as the length scale, and moderate interface state density (Dit) of 4.8×1011 cm−2 eV−1 for ZrO2 with interfacial layer. The Zr–Ge–silicate interfacial layer separately shows a low leakage current density of 3×10−2 A/cm2 at Vg of −1 V and Dit of 1×1012 cm−2 eV−1. Significant improvements in the charge trapping properties under Fowler–Nordheim constant current stressing in both ZrO2 with the interfacial layer and Zr–Ge–silicate layers have been observed.