THERMAL-STABILITY OF CU/COSI2 CONTACTED P+N SHALLOW JUNCTION WITH AND WITHOUT TIW DIFFUSION BARRIER

The thermal stability of Cu/CoSi2 contacted p+n shallow junction diodes with and without TiW diffusion barrier was investigated with respect to metallurgical reaction and electrical characteristics. Without the diffusion barrier, the Cu (2000 angstrom)/CoSi2 (700 angstrom)/p+n diodes (with a junction depth of 0.2 mum measured from the silicide surface) were able to sustain a 30 s rapid thermal annealing (RTA) in N2 ambient up to 450-degrees-C without losing the integrity of the devices characteristics. The Cu3Si phase was observed at the CoSi2/Si interface after 500-degrees-C annealing; the phase penetrated through the CoSi2 layer causing a catastrophic change in layer structure after 700-degrees-C annealing. With the addition of a 1200 angstrom thickness of TiW diffusion barrier between Cu and CoSi2, the junction diodes were able to sustain the RTA treatment up to 775-degrees-C without degrading the basic electrical characteristics, and no metallurgical reaction could be observed even after an 800-degrees-C annealing.