MAPPING OF DEFECTS AND THEIR RECOMBINATION STRENGTH BY A LIGHT-BEAM-INDUCED CURRENT IN SILICON-WAFERS

Knowledge of the correlation between the nature of recombining defects (extended crystallographic defects, impurities etc.) and the local electrical properties of wafers are necessary for the control of semiconductor materials. The control of the evolution of the electrical properties during the processing steps used to manufacture a device is of a great interest provided that the investigation technique is non-destructive. The light-beam-induced current (LBIC) mapping technique is able (1) to recognize and reveal the existence of extended crystallographic defects, such as grain boundaries, dislocations and stacking faults, when they recombine minority carriers; (2) to evaluate the recombination strength of the preceding defects and (3) to suggest the existence of impurity clouds or precipitates in the homogeneous regions of the wafers. In silicon wafers and devices, LBIC mapping can reveal bulk and surface defects, by changing the wavelength of the light only. The LBIC map can be transformed into a quantitative minority-carrier diffusion length L map in silicon, because the light beam excitation is compatible with the determination of L from the spectral variations in the photocurrent and in the light absorption coefficient in the near IR. Finally, LBIC maps can also be used to detect and evaluate any improvements associated with treatments such as hydrogenation, internal and external getterings.