The progress of modern day integrated circuit fabrication technology and packaging has made fault isolation using conventional emission microscopy via the top of the integrated circuit more difficult, if not impossible. This is primarily due to the use of increased levels and density of metal-interconnect, and the advent of new packaging technology, e.g. flip-chip, ball-grid array and lead-on-chip, etc. Backside photon emission microscopy, i.e. performing photon emission microscopy through the bulk of the silicon via the back of the integrated circuit is a solution to this problem. This paper outlines the failure analysis of sub-micron silicon integrated circuits using backside photon emission microscopy. Sample preparation, practical difficulties encountered and case histories will be discussed.