Separation of Front and Backside Surface Recombination by Photoluminescence Imaging on Both Wafer Sides

In this paper, we present a method to separate the front and the backside surface recombination based on two photoluminescence images: one taken from the front side of the wafer and one from the backside. We use a 790-nm laser with a penetration depth in silicon of only 11 μm. At such a shallow charge carrier generation, the surface recombination of the illuminated side affects the minority carrier density to a greater extent than the recombination of the nonilluminated side. To utilize this effect, we calculate the ratio of the front side and the back side lifetime image. This ratio image allows an easy distinction not only of surface defects from bulk defects but of front surface recombination from back surface recombination as well. With a simple calculation, even quantitative surface recombination velocities can be obtained.