Investigation of three-dimensional imaging of a silicon flip-chip using two-photon optical beam induced current microscopy

We describe a method for acquiring three-dimensional profiles of integrated circuits using the sensitive focal dependence of the two-photon optical beam induced current (TOBIC) effect. The device studied was a 0.35 μm feature size flip-chip with an exposed silicon substrate. The chip contained a standard test circuit used in a commercial application. The two-dimensional images we obtained showed some focal dependence and from this we inferred the possibility of using a peak detection algorithm, adapted from biological imaging, to generate a three-dimensional image from our data. Using interpolation we inferred the focal position corresponding to the peak photocurrent and recorded this for each two dimensional point to construct a surface profile representing the peak photocurrent focal depth.