Charge Collection Control Using Retrograde Well Tested by Proton Microprobe Irradiation

Soft error reduction by high-energy ion-implanted layers has been investigated by novel evaluation techniques using high-energy proton microprobes. A retrograde well formed by 160 and 700 keV boron ion implantation could completely suppress soft errors induced by the proton microprobes at 400 keV. The proton-induced current revealed the charge collection efficiency for the retrograde well structure. The collected charge for the retrograde well in the soft-error mapping was proved to be lower than the critical charge of the measured DRAMs (dynamic random-access memories). Complementary use of soft-etror mapping and ion-induced-current measurement could clarify well structures immune against soft errors.