Three-dimensional nanoscale subsurface optical imaging of silicon circuits

Three-dimensional subsurface imaging through the back side of a silicon flip chip is reported with a diffraction-limited lateral resolution of 166nm and an axial performance capable of resolving features only 100nm deep. This performance was achieved by implementing sample-scanned two-photon optical beam induced current microscopy using a silicon solid immersion lens and a peak detection algorithm. The excitation source was a 1530nm erbium:fiber laser, and the lateral optical resolution obtained corresponds to 11% of the free-space wavelength.