DETERMINATION OF THE DEFECT DEPTH PROFILE AFTER SAW CUTTING OF GAAS WAFERS MEASURED BY POSITRON-ANNIHILATION

Positron Lifetime measurements and Doppler broadening spectroscopy usi ng slow positrons were combined to investigate open-volume defects cre ated by sawing wafers from GaAs ingots by a diamond saw cutter. It was found during step-by-step polishing that the depth distribution repre sents a wedgelike profile. The depth and the concentration of the defe cts introduced by the diamond saw depend on the advance of the saw bla de. An isochronal annealing experiment was carried out to study the th ermal stability of the observed defects. The positron lifetime of the dominant open-volume defect was estimated to be. larger than 330 ps. I t was concluded from this lifetime value and from the Doppler broadeni ng parameters as well as from the annealing behavior that vacancy aggr egates consisting of at least two vacancies are created by the sawing procedure. More extended defects such as microcracks were analyzed by scanning electron microscopy. (C) 1998 American Institute of Physics. [S0021-8979(98)04516-2].