The Effect of Implant Temperature and Pre-Annealing on Defect Formation after Laser Thermal Processing

摘要

Laser thermal processing (LTP) involves the formation of ultra-shallow, low resistivity junctions by melting preamorphized Si. Extended defects have been shown to form upon recrystallization of the molten layer. These regrowth-related defects appear to originate at the implant induced amorphous/ crystalline (a/c) interface however the source of the defects is unclear. In order to investigate the origin of these defects, two different mechanisms have been used to alter the roughness of the a/c interface created by a 10keV Si~+ 1 * 10~(15) cm~(-2) amorphizing implant prior to melting and recrystallization by LTP. The first method involved changing the implant temperature of the implant. The 10keV 1 * 10~(15) cm~(-2) Si~+ implants were carried out at temperatures of -90 °C, 0 °C, 20 °C and 50 °C. HR-XTEM showed that the interfacial roughness decreased from around 30 to 12 as the implant temperature increased. Quantitative plan- view TEM (PTEM results show that there is a significant reduction in the extended defect density with decreasing interfacial roughness. The second method of changing the roughness involved using very low temperature anneals (VLTA) prior to LTP. Depending on the time, annealing below 500 C can change the roughness of the interface without inducing significant recrystallization of the amorphous layer by soldi phase regrowth. High resolution cross-sectional transmission electron microscopy (HR-XTEM) showed that a 400 °C 60 minute VLTA in N_2 gas reduces the interfacial roughness from 45 to 15. PTEM results again show that as the roughness of the a/c interface decreased the extended defect density also decreased. These results and the results of third experiment involving variation of the dose rate can all be plotted on a single graph relating the roughness to the defect density.