Low Energy Electron Microscopy Utilized in Dynamic Circuit Analysis and Failure Detection on LSI-VLSI Internal Circuits

Nonloading and nondestructive signal probing of state-ofthe-art semiconductor arrays has been achieved with the electron beam (E-beam) probe, utilizing scanning electron microscopes (SEM's). To apply the electron beam circuit prober successfully, a low energy setup was developed in order to prevent damage which can be caused by any high energy electrons interacting with the sample in the typical SEM. Using a converted SEM (AMR 1000) with primary beam energies below 770 eV, the accumulation of trapped charges in the quartz or polymide surface insulators was prevented. The probable electron penetration depth with these low energy electrons corresponds to 10 nm or less on conventional silicon based microcircuits. The greatest concerns connected to the usage of very low energy beams were the lack of adequate spatial resolution and the available sample beam current (illumination), especially when using tungsten cathodes. These two concerns are eliminated, as our results have demonstrated better than 100 nm spatial resolution when using 750 eV primary beam energy, and adequate brightness even with a 360 eV beam when it is applied in the stroboscopic mode with less than 1 ' percent duty cycle.