Patent ID: 7491632

Claim:
A method of fabricating a semiconductor structure comprising: forming a buried subcollector region having a dopant concentration of about 10 18 atoms/cm 3 or greater and an upper junction that is located at a depth from about 3000 Å or greater from an upper surface of a semiconductor substrate, said forming including providing a patterned mask on said upper surface of said semiconductor substrate, said patterned mask having at least one opening that exposes a portion of said upper surface of said semiconductor substrate, ion implanting a dopant ion through said at least one opening at an ion implant energy of about 500 keV or less and an ion dose of about 10 14 atoms/cm 2 greater, and removing said patterned mask; and forming an epitaxial semiconductor layer on said upper surface of said semiconductor substrate, wherein all of said buried subcollector remains buried within said semiconductor substrate after formation of said epitaxial semiconductor layer.