Forming adjacent impurity regions in a semiconductor by oxide masking

A method for forming adjacent impurity regions of differing conductivities in a semiconductor substrate without using lithography. N type impurities of a first conductivity are introduced into the substrate to form first impurity regions. The substrate is then oxidized to create a mask having a thickness which is greater over the N type impurity regions than over the remainder of the substrate. A portion of the masking layer is then removed, preferably by dip-etching, to a depth which is sufficient to re-expose the substrate only. Impurities of a second conductivity are then introduced in the substrate adjacent the N type impurity regions, with the remaining portion of the mask protecting the N type impurity regions from introduction of the second impurities therein.