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 typical contaminants of packaging or wiring materials. Suppression of carrier collection by a retrograde well or an epitaxial layer has been investigated 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 retrograde well with a buried layer on a Si wafer, and on an epitaxial wafer has been investigated for DRAM application using the ion-beam-induced-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⁺p diodes with retrograde well structures were fabricated by B⁺ implantation at 0.4-1.3 μm and to doses of 3.5 × 10¹⁶-3.4 × 10¹⁷ ions/cm³. It should be noted that an increase in the B⁺ implantation dose effectively reduces carrier collection efficiency, though a buried layer implanted with a higher dose degrades the characteristics of devices by the increase in leakage current. The carrier collection efficiency of the n⁺p 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.