Formation of cobalt silicided shallow junction using implant into through silicide technology and low temperature furnace annealing

Abstract

This work investigates the shallow CoSi2 contacted junctions formed by BF2+ and As+ implantation, respectively, into/through cobalt silicide followed by low temperature furnace annealing, For p(+)n junctions fabricated by 20 keV BF2+ implantation to a dose of 5 x 10(15) cm(-2), diodes with a leakage current density less than 2 nA/cm(2) at 5 V reverse bias can be achieved by a 700 degrees C/60 min annealing. This diode has a junction depth less than 0.08 mu m measured from the original silicon surface, For n(+)p junctions fabricated by 40 keV As+ implantation to a dose of 5 x 10(15) cm(-2), diodes with a leakage current density less than 5 nA/cm(2) at 5 V reverse bias can be achieved by a 700 degrees C/90 min annealing; the junction depth is about 0.1 mu m measured from the original silicon surface. Since the As+ implanted silicide film exhibited degraded characteristics, an additional fluorine implantation was conducted to improve the stability of the thin silicide film, The fluorine implantation can improve the silicide/silicon interface morphology, but it also introduces extra defects. Thus, one should determine a tradeoff between junction characteristics, silicide film resistivity, and annealing temperature.