Electrical characterization of ultra-shallow junctions formed by diffusion from a CoSi/sub 2/ layer

Ultra-shallow p/sup +//n and n/sup +//p junctions were fabricated using a Silicide-As-Diffusion-Source (SADS) process and a low thermal budget (800-900/spl deg/C). A thin layer (50 nm) of CoSi/sub 2/ was implanted with As or with BF/sub 2/ and subsequently annealed at different temperatures and times to form two ultra-shallow junctions with a distance between the silicide/silicon interface and the junction of 14 and 20 nm, respectively. These diodes were investigated by I-V and C-V measurements in the range of temperature between 80 and 500 K. The reverse leakage currents for the SADS diodes were as low as 9/spl times/10/sup -10/ A/cm/sup 2/ for p/sup +//n and 2.7/spl times/10/sup -9/ A/cm/sup 2/ for n/sup +//p, respectively. The temperature dependence of the reverse current in the p/sup +//n diode is characterized by a unique activation energy (1.1 eV) over all the investigated range, while in the n/sup +//p diode an activation energy of about 0.42 eV is obtained at 330 K. The analysis of the forward characteristic of the diodes indicate that the p/sup +//n junctions have an ideal behavior, while the n/sup +//p junctions have an ideality factor greater than one for all the temperature range of the measurements. TEM delineation results confirm that, in the case of As diffusion from CoSi/sub 2/, the junction depth is not uniform and in some regions a Schottky diode is observed in parallel to the n/sup +//p junction. Finally, from the C-V measurements, an increase of the diodes area of about a factor two is measured, and it is associated with the silicide/silicon interface roughness.