Evaluation of Detection Efficiency of Atom Probe Tomography

抄録

  Atom probe tomography (APT) is a widely used technique to evaluate the atomic structure of semiconductor materials such as the field effect transistor. However, application of the APT technique faces difficulties, among which is the low reliability of reconstruction calculations due to poor understanding of the field evaporation mechanism. In general, lower detection efficiencies are observed in low evaporation field elements that undergo DC evaporation in APT. However, in the analysis of SiO₂ and GaAs, the detection efficiencies of oxygen and arsenic are higher than those of silicon and gallium, even though oxygen and arsenic have higher evaporation fields. To explain these phenomena, we evaluated the potential for neutral desorption from the sample surface without ionization in the APT analysis. We observed changes in the detection efficiencies of arsenic and phosphorus during analysis of InGaAsP, when the laser power and initial temperature were varied. This was attributed to increases in the temperature of the surface atoms during irradiation of the pulsed laser. Therefore, under the ultrahigh vacuum conditions applied in the experiment, the low vapor pressure elements might have experienced sublimation.