T. Yeoh, S. LaLumondiere, N. Ives, M. Leung, The Aerospace Corporation, El Segundo, CA

Summary: An oblique illumination method for imaging the backside of a microelectronic device is presented. This illumination allows for imaging through full thickness silicon without the need for special coatings or optics, with contrasts approaching that of laser confocal microscopy. Oblique illumination removes surface scattering effects, which improves the contrast immensely. The refraction of the oblique illumination through the high index of refraction silicon substrate (hence the term "refraction assisted-illumination (RAIL)") provides a near bright-field illumination condition underneath the surface. In this paper we present material detailing the effects of illumination direction on the quality of the images.