Nondestructive Internal Observation of Metal-Oxide-Semiconductor LSI Designed by 0.8 µm Rule

A metal-oxide-semiconductor (MOS)-LSI chip was designed by the 0.8 µm rule, and a passivated film on the chip was etched off while keeping the chip mounted on a ceramic package. The acoustic signal generated by irradiation of a chopped electron beam was picked up by a piezoelectric detector (PZT element) attached to the back of the package. The results of observation by electron-acoustic microscopy (EAM) are as follows: (a) the observable depth ( t x ) was proportional to the electron range ( R e ); (b) t x shifted to a shallower side (about 50% of R e ) compared to the case of bipolar transistors; (c) contact holes (0.8 µm 2 ) were distinctly observed at HV =19 kV; and (d) the resolution of our EAM was estimated to be about 0.4 µm at a chopping frequency of the electron beam of 1 MHz and an acceleration voltage of 18–19 kV.