Solid Phase Recrystallization Induced By Multi-Pulse Nanosecond Laser Annealing

The solid phase recrystallization of partially amorphized SOI structures using a pulsed Ultra-Violet Nanosecond Laser Annealing (UV-NLA) is reported. It is shown that combining UV-NLA process with a heating chuck at low temperature (450 degrees C) results in the perfect recrystallization of the amorphized portion of the silicon layer. Actually, sub-melt multi-pulse UV-NLA enables obtaining the total crystal recovery and a very high dopant activation rate, comparable to melt laser annealing approaches or high temperature rapid thermal annealing, with a very low overall thermal budget. This approach is a great alternative to traditional solid phase epitaxial regrowth process, which reach it limits, in terms of recrystallization rate, at temperatures lower than 500 degrees C. The process presented here is thus suitable for integration paths in which the thermal budget must be limited as for example 3D sequential integration. Besides the high activation rate, another benefit of the solid phase recrystallization, compared to an equivalent laser anneal in the melt regime, is the almost unchanged surface roughness. Furthermore, the use of an in-situ metrology based on Time Resolved Reflectometry (TRR) enables the monitoring of the crystalline seed thickness evolution during UV-NLA and the estimation of the recrystallization rate.