Push-back junction isolation semiconductor structure and method

A junction-isolated tub for use in fabricating circuit components in a silicon integrated circuit comprising a silicon substrate of one conductivity type, an epitaxial silicon layer of opposite conductivity type grown on a surface of said silicon substrate, a diffused isolation region of said one conductivity type extending from a surface of said epitaxial layer to said substrate, said isolation region surrounding a region of said epitaxial layer and forming an electrical junction therewith to form an isolated region of opposite conductivity type, said diffused isolation region having a concentration gradient of dopant of said one conductivity type which decreases from the center of the diffused isolation region outwardly toward its edge, said region of said isolated region of said epitaxial layer having a surface concentration of said dopant of opposite conductivity type at said junction with the isolation region which is higher than the dopant concentration in the underlying epitaxial layer and higher than the dopant concentration near the edge portion of said isolation region to thereby compensate the dopant concentration near the edge portion of said isolation region to convert said edge portion to said opposite conductivity type, and thereby providing an increased area of said region of said opposite conductivity type isolated by said isolation region.