Ballistic-Electron-Emission Microscopy on Epitaxial Silicides

Abstract

Ballistic-electron-emission microscopy (BEEM) and spectroscopy (BEES) applied to epitaxial CoSi₂/Si interfaces are reviewed. Interfacial dislocations in 2–3-nm-thick CoSi₂(001)/Si(001) films with Burgers vector b=a/4 lower the barrier height by almost 0.1 eV at 77 K. This corresponds to a decrease in the Schottky barrier height Φ_B at the metallurgical interface from Φ_B=0.74±0.03 eV, characteristic of defect-free regions, to near zero within the range of the strain field of a few nanometers. In contrast, the dislocations of type b=a/6 present at CoSi₂/Si(111) interfaces do not affect the barrier height. CoSi₂/Si(111) films are more suitable for studying interfacial scattering by BEEM than CoSi₂/Si(100) films, because of their simpler surface structure and because of band structure effects. Here, individual point defects can be resolved. Their spatial distribution indicates diffusion along the interface during film growth. By analysing the shape of BEES spectra obtained on isolated point defects, and by making use of the projected band structure predicting the BEES current to set in ∼0.2 eV above the Schottky barrier, it may be concluded that the defects are located at the interface.