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 Sili cide-As-Diffusion-Source (SADS) process and a low thermal budget (800- 900 degrees C). A thin layer (50 nm) of CoSi2 was implanted with As or with BF2 and subsequently annealed at different temperatures and time s to form two ultra-shallow junctions with a distance between the sili cide/silicon interface and the junction of 14 and 20 nm, respectively, These diodes were investigated by I-V and C-V measurements in the ran ge of temperature between 80 and 500 K. The reverse leakage currents f or the SADS diodes were as low as 9 x 10(-10) A/cm(2) for p(+)/n and 2 .7 x 10(-9) A/cm(2) for n(+)/p, respectively, The temperature dependen ce of the reverse current in the p(+)/n diode is characterized by a un ique 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 in dicate that, the p(+)/n junctions have an ideal behavior, while the n( +)/p junctions have an ideality factor greater than one for all the te mperature range of the measurements. TEM delineation results confirm t hat, 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 increas e of the diodes area of about a factor two is measured, and it is asso ciated with the silicide/silicon interface roughness.