Patent ID: 8728904

Claim:
A method of forming an isolation structure in a semiconductor substrate of a first conductivity type in the absence of an epitaxial layer, the method comprising: forming a single mask layer on a flat top surface of the semiconductor substrate using only one mask step; forming an opening in the single mask layer such that a sidewall of the single mask layer around the opening is sloped, a thickness of the single mask layer decreasing continuously from a first thickness at an outer periphery of the opening to a significantly smaller second thickness at an inner periphery of the opening, the sloped sidewall lying between the outer periphery and the inner periphery of the opening; and implanting a dopant of a second conductivity type opposite to the first conductivity type through the flat top surface into the semiconductor substrate, the dopant being implanted at an implantation energy such that directly below the opening the dopant forms a floor isolation region with an upper junction located below the top surface of the semiconductor substrate, the dopant not penetrating the single mask layer where the single mask layer has the first thickness, the dopant forming a sidewall isolation region directly beneath the continuously sloped sidewall of the single mask layer, the sidewall isolation region extending continuously from the floor isolation region to the flat top surface so as to enclose an isolated region of the first conductivity type.