Application of excimer laser annealing in the formation of ultra-shallow p⁺/n junctions

In this study, we have simulated the melt front and temperature distribution profiles for pre-amorphized Si during laser irradiation. The simulation data show that theoretically, it is possible to melt the whole amorphous layer without melting the underlying crystalline substrate. On the other hand, ultra-shallow p⁺/n junctions were formed by ultra-low energy boron ion implantation into pre-amorphized silicon substrates. Dopant activation was achieved via spike rapid thermal annealing (RTA) and pulsed excimer laser annealing. Secondary ion mass spectrometry (SIMS) analyses show that a step-like dopant profile can be obtained with a single-pulse laser irradiation. Such a profile is in sharp contrast with the boron concentration profile that is obtained after spike RTA. The cross-sectional transmission electron microscopy images show that the entire pre-amorphized layer has been recrystallized to single-crystalline (100) Si after laser annealing. The results clearly indicate the advantages of employing laser anneal as compared to RTA in the fabrication of highly activated and abrupt ultra-shallow junctions.