Effect of Laser Thermal Processing on Defect Evolution in Silicon

Laser Thermal Processing (LTP) involves laser melting of an implantation induced preamorphized layer to form highly doped ultra shallow junctions in silicon. In theory, a large number of interstitials remain in the end of range (EOR) just below the laser-formed junction. There is also the possibility of quenching in point defects during the liquid phase epitaxial regrowth of the melt region. Since post processing anneals are inevitable, it is necessary to understand both the behavior of these interstitials and the nature of point defects in the recrystallized-melt region since they can directly affect deactivation and enhanced diffusion. In this study, an amorphizing 15 keV 1 x 1015/cm2 Si+ implant was done followed by a 1 keV 1 × 1014/cm2 B+ implant. The surface was then laser melted at energy densities between 0.74 and 0.9 J/cm2 using a 308 nm excimer-laser. It was found that laser energy densities above 0.81 J/cm2 melted past the amorphous-crystalline interface. Post-LTP furnace anneals were performed at 750°C for 2 and 4 hours. Transmission electron microscopy was used to analyze the defect formation after LTP and following furnace anneals. Secondary ion mass spectrometry measured the initial and final boron profiles. It was observed that increasing the laser energy density led to increased dislocation loop formation and increased diffusion after the furnace anneal. A maximum loop density and diffusion was observed at the end of the process window, suggesting a correlation between the crystallization defects and the interstitial evolution.