Patent ID: 7846805

Claim:
A method of forming a device comprising: providing a substrate with a first transistor region separated from other regions by first isolation regions, wherein the substrate is prepared with a collector mask exposing the first transistor region; implanting dopants of a first dopant type using the collector mask to form a collector region of a first type transistor; implanting dopants of a second dopant type using the collector mask to form a base region in the collector region; forming a composite protection stack in the first transistor region over the base region, wherein the composite protection stack comprises a dielectric layer with an opening and a doped layer having dopants of the first dopant type above the dielectric layer and filling the opening; annealing the substrate to diffuse dopants from the doped layer into the base region to form an emitter region of the first dopant type; and wherein a first buried doped well of the second dopant type is disposed below the collector region, and a second buried doped well of the first dopant type is disposed above the first buried doped well.