TiSi2thickness limitations for use with shallow junctions and SWAMI or LOCOS isolation

We have examined the impact of TiSi2formation on the properties of shallow n⁺and p⁺junctions (0.17-0.20 µm) in Si. The deposited Ti thickness varied from 300 to 1000 Å. The p⁺junctions developed high leakage currents after a reaction with Ti of initial thickness greater than 700 Å while the n⁺junctions were not degraded. In these studies LOCOS isolation was used and the TiSi2was formed away from the island edges. Additional experiments were performed on n⁺and p⁺diodes using SWAMI isolation with the TiSi2formed right up to the edges of the isolation. From step-height, spreading resistance, and RBS measurements, it was found that the thickness of TiSi2formed 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. The result was supported by SIMS measurements, which also showed an accumulation of atomic fluorine at the TiSi2interface (on p⁺diodes only). Cross-sectional transmission electron microscopy was used to examine the silicide morphology and interface planarity.