ACOUSTIC-EMISSION DURING LASER ANNEALING OF SILICON SINGLE-CRYSTALS

The acoustic response of silicon single crystals to the action of a mi llisecond laser pulse, with an excitation wavelength 1.06 mu m, has be en investigated. It has been discovered for the first time that additi onal acoustic emission, delayed in time with respect to the photoacous tic response, is observed for laser energy flux density above the thre shold corresponding to surface melting. The delay time depends linearl y on the laser radiation power and varies from one to tens of millisec onds. It is shown, by comparing the parameters of the acoustic emissio n with the dynamical development of thermoelastic stresses in the lase r action zone as well as with the kinetics of melting of the irradiate d surface, that crack formation under the action of the thermoelastic stresses is the source of the additional acoustic emission. (C) 1997 A merican Institute of Physics.