SUPPRESSION OF CHARGE-CARRIER COLLECTION IN DIODE WITH RETROGRADE WELL AND EPITAXIAL LAYERS FOR SOFT-ERROR IMMUNITY

One of the solutions to the reduction of soft errors is suppression of carrier collection generated by an energetic particle emitted from ty pical contaminants of packaging or wiring materials. Suppression of ca rrier collection by a retrograde well or an epitaxial layer has been i nvestigated by nuclear microprobes to clarify the validity of various well structures against soft errors in dynamic random access memories (DRAMs). The carrier collection efficiency of a retrograde well, a ret rograde well with a buried layer on a Si wafer, and on an epitaxial wa fer has been investigated for DRAM application using the ion-beam-indu ced-current (IBIC) measurement. The collection of carriers induced by proton microprobe irradiation could be reduced by the retrograde well formed at different boron doses. n(+) diodes with retrograde well stru ctures were fabricated by B+ implantation at 0.4-1.3 mu m and to doses of 3.5 x 10(16)-3.4 x 10(17) ions/cm(3). It should be noted that an i ncrease in the B+ implantation dose effectively reduces carrier collec tion efficiency, though a buried layer implanted with a higher dose de grades the characteristics of devices by the increase in leakage curre nt. The carrier collection efficiency of the ntp diode with the higher dose retrograde well can be reduced by more than half compared to the diode with a retrograde well in an epitaxial layer.