Carrier density and lifetime imaging of silicon wafers by infrared lock-in thermography

We present the lock-in carrier density imaging technique (CDI) as a non-contacting method for fast spatially resolved lifetime measurements. The method uses a novel lock-in thermography system with a fast infrared camera to detect the free-carrier absorption of photo-generated excess carriers. The spatial resolution depends on the camera chip and the optical setup of the measurement only. The resolution in carrier lifetime is demonstrated to be sufficient for the investigation of multicrystalline silicon wafers. The overall measurement time for a complete wafer is in the order of seconds, depending on the required lifetime resolution. This is orders of magnitude faster than other standard measurement techniques for lifetime maps. The CDI method demonstrates the feasibility of spatially resolved measurements on a time and sensitivity scale which is promising for the use in industrial applications.