Investigation of body-tie effects on ion beam induced charge collection insilicon-on-insulator FETs using the Sandia nuclear microprobe

Silicon-on-insulator (SOI) technology exhibits three main advantages over b ulk silicon technology for use in radiation environments. (1) SOI devices a re immune to latchup, (2) the volume of the sensitive region (body) and hen ce total charge collection per transient irradiation is much reduced in SOI devices and (3) the insulating layer blocks charge collection from the sub strate (i.e., no funneling effect). This effectively raises the single even t upset (SEU) threshold for the SOI device. However, despite their small ac tive volume SOI devices are still vulnerable to single event effects (SEE). Inherent in the SOI transistor design is a parasitic npn bipolar junction transistor (BJT), where the source-body-drain acts as an emitter-base-colle ctor BJT. An ion strike to a floating (not referenced to a specific potenti al) body creates a condition where the excess minority carriers in the drai n-body cause the parasitic BJT to turn on and inject more charge into the d rain than was deposited in the device by the ion. In extreme cases the floa ting body effect (FBE) can trigger a high-current state called single-event snapback (SES) where channel conduction is sustained indefinitely through regenerative electron-impact ionization near the drain junction. Tying the body to the source limits the emitter-base current and reduces the sensitiv ity of the device to single ion strikes. Unfortunately, the body-tie loses effectiveness with distance due to resistivity, and in regions far enough f rom the tie the BJT is still in effect. Using the Sandia nuclear microprobe we have created charge collection maps on Sandia CMOS6rs SOI FETs of varyi ng channel widths. These devices have body ties at both ends of the channel region. Results clearly demonstrate that distance of the ion strike from t he body tie has an inverse effect upon charge collection and SES sensitivit y due to the resistivity of the channel. Experimental results compare well with DAVINCI simulations and electrically induced snapback thresholds. In a ddition, an interesting saturation effect of SES versus the amount of injec ted charge is observed. (C) 2001 Elsevier Science B.V. All rights reserved.