Hot-electron effects and oxide degradation in MOS structures studied with ballistic electron emission microscopy

Abstract

The application of the STM-based technique of ballistic electron emission microscopy (BEEM) to the study of transport properties of SiO 2 gate oxide layers is reviewed. Oxide degradation observed on a local scale of nanometer dimensions ranges from the filling of electron traps with low-kinetic-energy electrons injected just above the oxide barrier, to trap generation and filling triggered by electrons with kinetic energies տ2 eV. BEEM provides means to determine the spatial distributions of the traps. Only positively charged traps are observed for thin (Շ4 nm) SiO 2 layers upon electrical stressing. Oxide breakdown is seldom induced by local stressing, suggesting that it occurs at extrinsic defect sites that are widely separated. BEEM also provides unique opportunities to address fundamental issues. In that regard, examples of the dynamic response of the SiO 2 dielectric to a moving electron are presented, as well as the determination of the dispersion of the electron mass of the conduction-band electrons. The latter is achieved by modeling quantum interference oscillations in the BEEM current.

Hot carrier transport effects in Al2O3-based metal-oxide-semiconductor structures

“…Once in position, a grounding contact consisting of a fine Pt-Rh wire was manipulated onto a selected metal dot for current-voltage (I -V) measurements and for characterization by ballistic electron emission microscopy ͑BEEM͒. 15,18 The I -V measurements permitted an estimate of the quasi-static capacitance-voltage characteristics since the voltage ramp in our instrument is stepped rather than continuous.…”

Breakdown characteristics of interconnect dielectrics

“…Tt turns out that under electric fields above 1 MVlcm, as for the range of fields used for accelerated dielectric breakdown testing and lifetime evaluation, the kinetic energy distribution of the electrons may not be fully thermalized with the substrate temperature. [21,22,23] Brorson et al 1221 measured the energy distribution of hot electrons that were injected into vacuum through a thick (up to 150nm) SiO, film. For fields b2 MV/cm in the oxide, the distributions peaked at -2eV, with a width (electron temperature) that increased with increasing field.…”

Effect of surface contamination on electron tunneling in the high bias range

“…When performing BEEM measurement of metal=oxide samples, pioneering groups 14,15 usually degassed the samples in UHV to remove water vapor and organic contamination from the oxide surface before depositing the thin metal film. Cai et al 16 also mentioned that degassing was necessary to observe BEEM current for their Pt=Sc 2 O 3 sample.…”