Spatially Resolved Characterisation of Silicon As-cut Wafers with Photoluminescence Imaging

The characterization of silicon as-cut wafers is important for process control in solar cell production, since it can serve as starting material quality inspection and give information about a change of material properties caused by different process steps. In particular, spatially resolved characterization tools such as Photoluminescence Imaging (PLI) are useful as an information source. Due to the low signal in a luminescence image of an as-cut wafer a major problem is superimposed laser reflection light if the detection occurs from the illuminated side of the wafer. We present a method which eliminates the spurious reflection contribution by a special image correction technique. The image correction is based on a separate measurement of a reflection topography of the as-cut wafer surface. Additionally we show that for non calibrated luminescence images of as-cut material the bulk lifetime in low quality areas can be estimated by relating PL-intensity in these areas to a saturated PL-intensity value that can be assigned to high quality areas via a simulated curve of relative PL-intensity over minority carrier bulk lifetime. Copyright # 2008 John Wiley & Sons, Ltd.