Reliability of ultra thin ZrO 2 films on strained-Si

Abstract

Ultra thin high- k zirconium oxide (equivalent oxide thickness ∼1.57 nm) films have been deposited on strained-Si/relaxed-Si 0.8Ge 0.2 heterolayers using zirconium tetra- tert-butoxide (ZTB) as an organometallic source at low temperature (<200 °C) by plasma enhanced chemical vapour deposition (PECVD) technique in a microwave (700 W, 2.45 GHz) plasma cavity discharge system at a pressure of 66.67 Pa. The trapping/detrapping behavior of charge carriers in ultra thin ZrO 2 gate dielectric during constant current (CCS) and voltage stressing (CVS) has been investigated. Stress induced leakage current (SILC) through ZrO 2 is modeled by taking into account the inelastic trap-assisted tunneling (ITAT) mechanism via traps located below the conduction band of ZrO 2 layer. Trap generation rate and trap cross-section are extracted. A capture cross-section in the range of ∼10 −19 cm 2 as compared to ∼10 −16 cm 2 in SiO 2 has been observed. The trapping charge density, Q ot and charge centroid, X t are also empirically modeled. The time dependence of defect density variation is calculated within the dispersive transport model, assuming that these defects are produced during random hopping transport of positively charge species in the insulating layer. Dielectric breakdown and reliability of the dielectric films have been studied using constant voltage stressing. A high time-dependent dielectric breakdown (TDDB, t bd > 1500 s) is observed under high constant voltage stress.