Reduced soft error rate (ser) construction for integrated circuit structures

Abstract

An integrated circuit structures such as an SRAM construction wherein the soft error rate is reduced comprises an integrated circuit structure formed in a semiconductor substrate, wherein at least one N channel transistor is built in a P well adjacent to one or more deep N wells connected to the high voltage supply and the deep N wells extend from the surface of the substrate down into the substrate to a depth at least equal to that depth at which alpha particle-generated electron-hole pairs can effectively cause a soft error in the SRAM cell. For a 0.25 &mgr;m SRAM design having one or more N wells of a conventional depth not exceeding about 0.5 &mgr;m, the depth at which alpha particle-generated electron-hole pairs can effectively cause a soft error in the SRAM cell is from 1 to 3 &mgr;m. The deep N well of the 0.25 &mgr;m SRAM design, therefore, extends down from the substrate surface a distance of at least about 1 &mgr;m, and preferably at least about 2 &mgr;m. In a preferred embodiment, the implantation of the substrate to form the deep N well of the improved SRAM of the invention is carried out in a manner which will cause straggle, i.e., cause the doped volume comprising the deep N well to broaden at its base. Such a broadened base deep N well will have enhanced opportunity to collect electrons generated by the alpha particle collision with the substrate. This deep N well with a broadened base can be formed either by increasing the implant energy or by tilting the substrate with respect to the axis of the implant beam while implanting the substrate to form the deep N well.