Quantifying the effects of uneven etching during the SIMS analysis of periodic doping structures grown by silicon MBE

Abstract

AbstractProblems associated with the secondary ion mass spectrometry (SIMS) depth profiling of periodic doping structures are discussed with reference to experiments on a boron‐in‐silicon modulation doping structure and a boron‐antimony silicon super‐lattice, both grown by silicon molecular beam epitaxy (MBE). The effects of uneven etching during SIMS analysis are compared with the effects of dopant diffusion during growth. Uneven etching is modelled with an algorithm in which the macrotopography of the crater base is described in terms of an unevenness function f(x, y). Simulation depth profiles involve passing craters of this topography f(x, y) through specified, laterally homogeneous, doping distributions ρp(z) in a series of equal depth interations. The predicted SIMS signal is proportional to the amount of dopant sputtered per depth iteration. The model explains the peak shapes and the loss of depth resolution with depth that are observed experimentally. The effects of dopant diffusion during growth are found by re‐heating parts of the wafer to the growth temperature for various periods of time and then SIMS depth profiling them (thermal cycling).