The impact of TiSi2 on shallow junctions

We have examined the impact of TiSi2 formation on the properties of shallow n+ and p+ junctions (0.17-0.20 um) in Si. The deposited Ti thickness was varied from 300A to 1000A. The p+ junctions developed high leakage currents after reaction with Ti of initial thickness greater than 700A while the n+ junctions were not degraded. In these studies LOCOS isolation was used and the TiSi2 was formed away from the island edges. Additional experiments were performed on n+ diodes using SWAMI isolation with the TiSi2 formed right up to the edges of the isolation. From step-height, spreading resistance and RBS measurements it was found that the thickness of TiSi2 formed on n+ Si was less than on p+ Si for a given initial Ti thickness. The amount of electrically active dopant remaining in the substrates was seen to decrease with increasing Ti thickness. This was supported by SIMS measurements which also showed an accumulation of atomic fluorine at the TiSi2 interface. Cross-sectional transmission electron microscopy was used to examine the silicide morphology and interface planarity.