Analysis of a thin, silicon-oxide, silicon-nitride multilayer target by time-of-flight medium energy backscattering

Initial results of a program to optimize the resolution of a time-of-flight medium energy backscattering system for analyses of thin oxide and oxynitride films on silicon are reported. Through a redesign of the time-of-flight spectrometer, it has been possible not only to reduce the timing uncertainty attributable to differing path lengths but also, by deliberately introducing small path length differences correlated with scattering angle, to significantly reduce the kinematic dispersion resulting from the finite solid angle of the instrument. Straggling and the energy distribution of the secondary electrons which generate the start signal remain as the primary contributors to system timing uncertainty. Initial measurements of SiO ₂ and Si ₃N ₄ multilayer films in the 10 nm thickness range have been made using channeling in the <110> direction of the Si substrate to suppress background. The depth resolution of the measurements appears to be ≈ 2 nm.