The sample is a test structure for electromigration experiments (Blech test).
It consists of Cu(Ag) alloy conductor lines embedded in Si oxide insulation with a Ta diffusion barrier.
The spectra are shown in their true intensity ratios. Prominent Auger peaks are labeled. The different background corresponds to the brightness in the secondary electron image and reflects the decreasing atomic number of the analyzed material from heavy Ta (#2) over Ag (#3), Cu (#1) to Si oxide (#4).
The secondary electron images show - from left to right – zooming to the position of the analysis areas in the test structure.