Optical characterization of laser processed ultra-shallow junctions

Laser thermal processing (LTP) and gas immersion laser doping (GILD) of ion-implanted silicon are studied experimentally as potential solutions to process ultra-shallow junctions of the future CMOS generations. Junctions with depths ranging from 10 to 150 nm are realized by LTP on B+ or BF2+ implanted Si wafers, with or without Ge+ pre-amorphization. A special attention has been paid to in situ and ex situ optical diagnostics in order to follow the laser induced phenomena. The melting/solidification process, which highly depends on the implanted ion and dose, and the dopant activation are real time monitored by transient reflectivity (TR) at 675 nm. The activated dopant dose and sheet resistance evolutions as a function of the laser fluence and shot number are deduced from IR spectroscopy of the processed samples. Comparison with sheet resistance measurements and secondary ion mass spectrometry (SIMS) depth profiles shows that optical diagnostics are very helpful tools to control the laser doping process.