Sample Preparation for Backside Failure Analysis Using Infrared Photoemission Microscopy

For conventional photoemission microscopy the silicon is thinned to a few tens of micrometres for backside imaging since silicon is opaque in the visble part of the spectrum. However, at wavelengths greater than approximately 1050 nm, most silicon is effectively transparent. Hence, the use of an infrared photoemission microscope (IRPEM) operating at wavelengths of 1100 to 2500 nm, usually eliminates the need for thinning, except where the silicon is heavily doped. However, the plastic encapsulation of packaged devices must be removed and the die surface polished. A polishing system has been evaluated and optimised for this purpose. Surface roughness (Ra) of 1 nm or better was obtained. Representative applications are shown and discussed.