Influence of Mg ion concentration in ZrO2 gate dielectric layered silicon based MOS capacitors for memory applications: Thorough understanding of conduction processes

摘要

Various high-K metal-oxide-semiconductor (MOS) capacitors with different concentrations of Mg doped ZrO2 (Mg:ZrO2) gate dielectric on p-type silicon (100) substrates were fabricated by using electron beam evaporation. A uniform and crack free dielectric layers of Mg:ZrO2 having RMS surface roughness in the range from 0.25 to 0.83 nm were achieved. The dielectric layers were structurally and electrically studied. Structural analysis from GIXRD and Williamson-Hall plots revealed that Mg incorporation into ZrO2 lattice has stabilized the tetragonal phase and the residual strain in the tetragonal stabilized Mg:ZrO2 layers had increased with increasing Mg concentration. Elemental composition studies of different layers in the MOS capacitors using Rutherford backscattering spectrometry (RBS) revealed the presence of very thin, unintentional and non-stoichiometric SiOx interfacial layer between dielectric and semiconductor interfaces. Thickness of the Mg:ZrO2 dielectric layers in the MOS capacitors measured by using RBS and cross-sectional field-emission scanning electron microscopy was in the range from 44.7 to 96.6 nm. A high dielectric constant of 29.8 with the equivalent oxide thickness of 6.5 nm was achieved in the 5 mol% Mg:ZrO2 dielectric layer. The hysteresis in the C-V characteristics of the MOS capacitors has been explained in detail based on the interactions of Mg ions with oxygen vacancies in the dielectric layer. Various conduction mechanisms have been elucidated to explain the leakage currents in the MOS capacitors. The decrease in Schottky and Poole-Frenkel barrier heights at the lower voltages (0 to - 3V) was found responsible for the increase in the leakage current as the Mg ion concentration was increased. Space charge limited conduction mechanism has been found to be dominant in larger applied voltage region (- 3V to -10V). The Fowler-Nordheim tunneling and trap-assisted tunneling were dominant at the higher negative voltage regions greater than -10V.