An
integrated circuit and method of fabricating the
integrated circuit is disclosed. The
integrated circuit includes vertical bipolar transistors (30, 50, 60), each having a buried collector region (26′). A carbon-bearing
diffusion barrier (28c) is disposed over the buried collector region (26′), to inhibit the
diffusion of
dopant from the buried collector region (26′) into the overlying epitaxial layer (28). The
diffusion barrier (28c) may be formed by incorporating a
carbon source into the epitaxial formation of the overlying layer (28), or by
ion implantation. In the case of
ion implantation of carbon or SiGeC, masks (52, 62) may be used to define the locations of the buried collector regions (26′) that are to receive the carbon; for example, portions underlying eventual collector contacts (33, 44c) may be masked from the carbon
implant so that
dopant from the buried collector region (26′) can diffuse upward to meet the contact (33). MOS transistors (70, 80) including the
diffusion barrier (28) are also disclosed.