Electrical characterization of ultra-shallow junctions formed by diffusion from a CoSi2 layer

Ultra-shallow p+/n and n+/p junctions were fabricated using a Silicide-As-Diffusion-Source (SADS) process and a low thermal budget (800-900 ¬?C). A thin layer (50 nm) of CoSi2 was implanted with As or with BF2 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 ?ó 10-10 A/cm2 for p+/n and 2.7 ?ó 10-9 A/cm2 for n+/p, respectively. The temperature dependence of the reverse current in the p+/n diode is characterized by a unique activation energy (1.1 eV) over all the investigated range, while in the n+/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+/n junctions have an ideal behavior, while the n+/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 CoSi2, the junction depth is not uniform and in some regions a Schottky diode is observed in parallel to the n+/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 suicide/silicon interface roughness. ¬© 1997 IEEE.