Physical Characterization of Novel Metal Electrodes for Hf-based Transistors

Abstract

Abstract. Metal electrode materials are being extensively evaluated as potential replacements for polysilicon in order to eliminate gate depletion, reduce gate resistance, overcome equivalent oxide thickness (EOT) scaling limitations and Fermi level pinning effects associated with the reaction between Hf-based dielectric films and the polysilicon electrode. High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) using X-ray spectra and electron energy loss spectra (EELS) were used to produce elemental profiles of dielectric and metal electrode constituents with particular emphasis on interfacial interactions. High spatial resolution chemical scan profiles of silicon, oxygen, nitrogen, and hafnium from the dielectric components in conjunction with various transition metals including hafnium, tantalum, molybdenum and ruthenium have been acquired to characterize the extent of material intermixing and crystallization as a function of deposition parameters and anneal temperature. The influence of the atomic percent Si in ternary compounds consisting of transition metal nitrides is presented within the context of Rutherford backscattering (RBS) composition data. Finally, factors influencing metal workfunction are presented based on physical and electrical characterization of high-k capacitors and transistors.

The Electrode‐Ferroelectric Interface as the Primary Constraint on Endurance and Retention in HZO‐Based Ferroelectric Capacitors

“…Last, valence band offsets (VBOs) and conduction band offsets (CBOs) were determined from XPS analysis and plotted as a function of leakage current density in Figure 6c. Despite previously reported differences in work function (WF) for the different TE materials, [ 35 ] no simple relation between the CBO and leakage current was observed, within experimental uncertainty. This is to be expected for a bulk trap mediated leakage mechanism, corroborating the multi‐phonon trap‐assisted tunneling model, which does not depend on charge injection into the conduction band.…”

“…Since RuO 2 lacks an interfacial layer formation, it is logical that the larger CBO in Figure 6c matches an expected larger WF (see Supporting Information for calculation). [ 35 ] Moreover, a different band alignment would be expected. Therefore a different conduction mechanism may be possible, which explains the lack of correlation of RuO 2 to the trends in Figures 6a,b.…”