Optimizing time-of-flight secondary ion mass spectrometry depth profiles of semiconductor heterostructures

Abstract

The continuous technological development of electronic devices and the introduction of new materials lead to ever greater demands on the fabrication of semiconductor heterostructures and their characterization. This work focuses on optimizing Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) depth profiles of semiconductor heterostructures aiming at a minimization of measurement-induced profile broadening. As a model system, a state-of-the-art Molecular Beam Epitaxy (MBE) grown multilayer homostructure consisting of natSi/28Si bilayers with only 2 nm in thickness is investigated while varying the most relevant sputter parameters. Atomic concentration-depth profiles are determined and an error function based description model is used to quantify layer thicknesses as well as profile broadening. The optimization process leads to an excellent resolution of the multilayer homostructure. The results of this optimization guide to a ToF-SIMS analysis of another MBE grown heterostructure consisting of a strained and highly purified 28Si layer sandwiched between two Si0.7Ge0.3 layers. The sandwiched 28Si layer represents a quantum well that has proven to be an excellent host for the implementation of electron-spin qubits.