Two-Photon Imaging Offers Backside Peek at Chips

Single-photon, optical beam-induced- current imaging is a valuable tool for the quality control of integrated circuits. However, this technique has become increasingly ineffective because of the large number of layers added to the front side of the modern chip. Scientists at Bell Laboratories in Murray Hill, N.J., have developed a two-photon process that can image through the back side of a chip without thermal absorption. In the process, a mode-locked Ti:sapphire laser "blasts" and polishes the back end of the chip. The team could view the components of a Hitachi 256 3 4k SRAM chip at around 10 µm, whether it was powered or not.