Dynamic Digital Modulation, an adaptation of Lock-In Thermography, has been shown to be a useful technique to establish the relative Z-depth of thermal sources in integrated circuits. In order to determine the specific depth of a thermal source it is necessary to correlate known depths to measured thermal rise time. In this work, multi-die stacked memory devices are used as calibration sources to correlate a thermal source at individual die to the measured thermal rise time.

The capability of the Scanning Electron Acoustic Microscopy (SEAM) technique for high resolution non-destructive subsurface imaging at different depths for a multi-level integrated circuit is assessed. Experimental results using a beveled DRAM IC sample are used to quantify the effect of the electron beam energy and modulation frequency on contrast, spatial resolution and depth of focus of SEAM amplitude and phase images.