ULTRA SHALLOW JUNCTION FORMATION USING DIFFUSION FROM SILICIDES .3. DIFFUSION INTO SILICON, THERMAL-STABILITY OF SILICIDES, AND JUNCTION INTEGRITY

The silicide-As-diffusion-source (SADS) process was studied for ultra shallow junction fabrication using TiSi2, CoSi2, NiSi, Pd2Si, and PtSi. The diffusion of both boron and arsenic from silicide into silicon was measured after cobalt silicide removal and was seen to be enhanced over conventional diffusion in Si. At 1100-degrees-C, the enhancement was greater for arsenic (almost-equal-to 100 times) than for boron (almost-equal-to 5 times); at 850-degrees-C, more normal diffusion was observed. The activation energy of the effective diffusivity is 5.3 eV for As and 4.7 eV for boron. Dopant evaporation affected the interface dopant concentration and thereby the diffusion depth in Si. The time limit, at which the silicide sheet resistance increased by 30% due to its thermal instability, was found to have an activation energy of approximately 5 eV in CoSi2, 3.5 eV in TiSi2, and 3.1 eV in PtSi. The thermal degradation of CoSi2 was slower for annealing in N2 than in Ar, and the degradation diffusivity was found to have nearly the same activation energy as dopant diffusion in Si from CoSi2. For uncapped silicides, all SADS diodes except TiSi2 As+, or CoSi2 and PtSi B+ junctions, showed high leakage current.