With the fast advance of ultra large scale integrated (ULSI) circuit technology, the need for sub-surface imaging
technique to locate and characterize sub-surface defects in ULSI circuits has been growing. In this study we advance
scanning thermal wave microscopy further so that the absolute phase lag of the thermal waves generated by an
electrically heated sub-surface microelectronic structure buried in an ULSI circuit can be measured. The measurement of
the absolute phase lag allowed exact locating of the vertical and horizontal position of buried microelectronic structures
and evaluation of their soundness nondestructively.