Non-Destructive Testing of Silicon Wafers by Monitoring Changes in Electron-Hole Plasma Reflectivity Caused by Wafer Defects
Original Publication Date: 1987-Feb-01
Included in the Prior Art Database: 2005-Jan-31
When a plasma of density N is created (as with a laser pump beam) in a well-defined spatial region of a Si wafer, Drude contributions modify the crystal's optical dielectric susceptibility e(l) in that region. Changes in e(l) or N are then monitored by measuring changes in the reflectivity (wR) and state of polarization of a probe beam incident on the excitation volume (V). Lattice defects which influence N are viewed as a change in Drude (plasma) contribution to (wR,(wP) in V. Therefore, by monitoring (wR,wP) everywhere on a wafer surface, one obtains a map of those wafer defects which influence carrier mobility or lifetime.