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

Abstract

This work investigates the shallow CoSi/sub 2/ contacted junctions formed by BF/sub 2//sup +/ and As/sup +/ implantation, respectively, into/through cobalt silicide followed by low temperature furnace annealing. For p/sup +/n junctions fabricated by 20 keV BF/sub 2//sup +/ implantation to a dose of 5/spl times/10/sup 15/ cm/sup -2/, diodes with a leakage current density less than 2 nA/cm/sup 2/ at 5 V reverse bias can be achieved by a 700/spl deg/C/60 min annealing. This diode has a junction depth less than 0.08 /spl mu/m measured from the original silicon surface. For n/sup +/p junctions fabricated by 40 keV As/sup +/ implantation to a dose of 5/spl times/10/sup 15/ cm/sup -2/, diodes with a leakage current density less than 5 nA/cm/sup 2/ at 5 V reverse bias can be achieved by a 700/spl deg/C/90 min annealing; the junction depth is about 0.1 /spl mu/m measured from the original silicon surface. Since the As/sup +/ 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.