Process of making dual well cmos semiconductor structure with aligned

Abstract

A process for making a CMOS dual-well semiconductor structure with field isolation doping, wherein only a single lithographic masking step is required for providing self-alignment both of the wells to each other and also of the field isolation doping regions to the wells. The lithographic masking step forms a well mask and defines an oxidation barrier which acts as: an implant mask (absorber) during the ion-implantation of a field dopant of one type; an oxidation barrier over one well during the oxidation of the opposite-type well to form over the one well a sacrificial oxide layer which forms the alignment marks for subsequent formation of the field-doping regions; and a dopant-transmitter during the ion-implantation of an opposite-type field dopant which is simultaneously absorbed by the sacrificial oxide. As a result, there are formed field-doped oxide layers self-aligned to the wells so that, with a subsequent masking step, oxide field isolations are defined over the doped oxide layers. A heat cycle is then used to drive the field dopants into the corresponding field-doping regions.