Interface and electrical properties of La-silicate for direct contact of high-k with silicon

Abstract: Chemical bonding states and electrical characteristics of a La-silicate formed as a compositional transition layer at La2O3/Si interface has been examined. A direct contact of a high-k gate dielectric with Si substrate has been achieved without forming SiO2-based interfacial layer by forming a compositionally graded La-silicate layer, which is advantageous for equivalent oxide thickness (EOT) scaling. A transistor operation with an EOT of 0.48nm has been demonstrated with low temperature annealing, however a degradation of effective mobility (μ eff) has been observed. A high μ eff of 300cm2/Vs with relatively low interfacial state density (D it) of 1011 cm−2/eV can be achieved when annealed at 500°C, indicating fairly nice interface properties of silicate/Si substrate. Mobility analysis has revealed an additional Coulomb scattering below an EOT of 1.2nm, which is in good agreement with the negative shifts in threshold and flatband voltages. Moreover, increase in D it and subthreshold slope have been observed while decreasing the EOT, suggesting the influence of metal atoms diffused from the gate electrode. A mobility degradation model is proposed using metal induced defects generation. [Copyright &y& Elsevier]