Simple, novel and low cost numerical aperture increasing lens system for high resolution infrared image in backside failure analysis

As is known to all, we could capture clearer infrared (IR) image from backside as Si substrate was thinner. But if we needed higher resolution image with conventional optical objective lens, we must introduce numerical aperture increasing lens(NAIL) technology or shorter wavelength light to improve numerical aperture (NA) in objective space. Now some vendors can provide NanoLens with NAIL but it is very expensive. In this paper, we proposed one simple and novel system of NAIL. Firstly, we fabricated two NAILs (one R≈3mm, the other R≈ 5mm) with glass material, and captured higher resolution IR image with NAIL help. Secondly, we found clearer image from smaller size NAIL by comparing IR images. Then, we studied how to moving NAIL on backside surface of die. Two moving methods were designed and we discussed their advantage and disadvantage, one of them was used in FA experiment. Although there were some limitation and disadvantage for this system, we believed this simple, novel and low cost NAIL system was beneficial to our FA from backside.