Dynamics of pulsed electron-beam annealing of ion-implanted semiconductors

Analysis of the physical phenomena occurring at pulsed annealing of ion-implanted semiconductors by a nanosecond electron beam (PEA) requires detailed information about the thermal regime in the surface layer of a sample which can be obtained only by numerical simulation. To make this the Stephan problem for the heat conduction equation was solved numerically by an energy cell method. The oscillographic time dependences of the accelerator collector current and diode voltage and the spatial distributions of absorbed energy obtained by the Monte Carlo method were introduced in the program as initial data. Dynamics of PEA of ion-implanted silicon and gallium arsenide samples by electron beams with a continuous electron spectrum, having the maximum energy up to 40 keV and the pulse duration of 50 to 500 ns was computed. The results have shown that the existence of high space and time gradients of temperature and the formation of extended and long-lived zones of a substance being in the metastable state between liquid-crystalline boundaries is a characteristic feature of the annealing of samples by electron beams with a duration of tens of nanoseconds. The velocity of crystallization front of the substance on cooling the sluch-zone achieves about 50 m/s, while the rate of cooling being about 109 degree/s. At such rates the formation of the defect layer is possible of a depth greater than the depth of melting. The size of the sluch-zone decreases with increase in pulse duration and decrease in spectral average energy that should result in the improvement of the quality of annealing observed in experiment. (author)