Varying implant dose rate for defect reduction in laser thermal processing

Laser thermal processing (LTP) of ion implanted silicon involves melting an d recrystallizing an implantation induced amorphous layer containing dopant s as a method of producing ultra shallow highly doped junctions in silicon. After LTP there can exist a high concentration of extended defects in the recrystallized region. These defects are commonly in the form of stacking f aults and microtwins that propagate from throughout the region that had bee n amorphous prior to laser melting. In order to determine the origin of the se extended defects, the effect of the dose rate of the silicon preamorphiz ation implant was studied. A 10 keV 1 x 10(15) cm(-2) Si+ implant was done into silicon at dose rates between 0.06 and 0.48 mA/cm(2). High-resolution cross-sectional transmission electron microscopy (HR-XTEM) results show the roughness of the amorphous crystalline interface increases with increasing close rate up to 0.24 mA/cm(2) then decreases because of dynamic annealing . Quantitative plan-view TEM results of the defect density after LTP proces sing at 0.75 J/ cm(2) laser power show a direct correlation between the amo rphous crystalline interface roughness and the final defect density. Reduct ion in amorphous/crystalline interface roughness prior to laser thermal pro cessing results in a dramatic reduction of LTP recrystallization defects. ( C) 2001 Elsevier Science Ltd. All rights reserved.