High Energy BSE/SE/STEM Imaging of 8 um Thick Semiconductor Interconnects

High energy (100-400 keV) scanning electron microscope (SEM) imaging of samples can be performed in the transmission electron microscope (TEM)/scanning TEM (STEM) when the system has secondary electron (SE) and/or backscattered (BSE) electron detector(s) installed. Previously, very high resolution SE imaging has been demonstrated at 200 keV in a STEM with a spherical aberration corrected condenser lens [1]. Additionally, imaging of semiconductor Cu interconnects in SiO2 dielectric located at distances > 3um below the surface has been accomplished using incident beam energies of 100-400 keV and a backscattered electron (BSE) detector [2]. In the high energy BSE analysis case, multilevel Cu interconnects are ideal structures to study because: 1) there is a large BSE yield difference between Cu and SiO2 so Cu can be easily detected and 2) Cu lines exist at multiple levels below the surface so multiple structures can be seen from different depths in one BSE image. In this paper, a semiconductor chip with 9 interconnect levels spanning 8 um in height was studied using SE, BSE and STEM imaging at incident beam energies of 300-400 keV in order to understand image content and quality versus the depth of the structure below the surface.