Praseodymium silicate films on Si(100) for gate dielectric applications: Physical and electrical characterization

Abstract

Praseodymium (Pr) silicate dielectric layers were prepared by oxidation and subsequent N2 annealing of thin Pr metal layers on SiO2∕Si(100) substrates. Transmission electron microscopy studies reveal that the resulting dielectric has a bilayer structure. Nondestructive depth profiling by using synchrotron radiation x-ray photoelectron spectroscopy shows that, starting from the substrate, the dielectric stack is composed of a SiO2-rich and a SiO2-poor Pr silicate phase. Valence and conduction band offsets of about 2.9 and 1.6eV, respectively, between the dielectric and the Si(100) substrate bands were deduced. Pr silicate films with an equivalent oxide thickness of 1.8nm show approximately three orders of magnitude lower leakage currents than silicon oxynitride references. Capacitance versus voltage measurements of the Pr silicate/Si(100) system report a flat band voltage shift of 0.22V, an effective dielectric constant of about 11 and a reasonably good interface quality with an interface state density on the order of 1011cm−2. Experimental results are supplemented by ab initio considerations which review the most probable mechanisms of fixed charge formation in the Pr silicate layers.