ULTRA SHALLOW JUNCTION FORMATION USING DIFFUSION FROM SILICIDES - SILICIDE FORMATION, DOPANT IMPLANTATION AND DEPTH PROFILING

Shallow junctions have been fabricated in a silicide-As-diffusion-source process using implantation of BF2 and As into thin silicides of cobalt, titanium, nickel, palladium, and platinum with emphasis on CoSi2. Ge-implantation was used in an attempt to amorphize the silicide prior to the boron introduction and thereby eliminate the possible channeling of boron in the polycrystalline silicide. Cross-section transmission electron microscopy (TEM) shows that Ge implantation created a heavily damaged layer of 10 nm in the silicide, which was restored to a polycrystalline state after annealing at 900-degrees-C for 10 s. For shallow boron depth profiling using secondary ion mass spectroscopy (SIMS), careful selection of the primary ion beam energy and angle was necessary to minimize ion beam mixing and shadowing due to surface roughness. The boron profile in a thick CoSi2, 300 nm, measured deeper than in a thin CoSi2, 50 nm, demonstrating the effect of SIMS shadowing. The effect of Ge-implantation on boron profiles was within the depth measurement error, indicating that no pronounced channeling had taken place in the silicide. Implant depths measured by SIMS agree well with those calculated by TRIM near the peak, but large deviations exist at the tail.