Abstract: Bipolar devices on a common substrate are formed in tubs defined by a sinker that is self-aligning with the isolating trench and provides a relatively low vertical resistance contact from a surface contact to the underlying buried layer. In a first embodiment, the isolating trench initially is defined only down to the top surface of the buried layer. The trench walls are then doped, and the dopant allowed to diffuse laterally through the trench sidewalls. The resultant sinker is self-aligned with the isolating trench. The trench depth is then further increased to a desired depth preferably penetrating into the substrate. Thereafter, a bipolar device is formed in the tub, preferably with the device collector adjacent the trench and thus aligned with the sinker. In a second embodiment, an opening is formed in the surface oxide defining the area where the trench (when formed) will be cut.

Abstract: A sinker which is self-aligned with the oxide isolating trench which is used to define the tub in which the complete bipolar device is located. In a preferred approach to the process for forming the sinker of this invention, little additional diffusion of the sinker occurs during subsequent processing, whereby an effective sinker, aligned with the collector of the bipolar device, is achieved without additional masking steps.