Patent ID: 6984872

Claim:
A bipolar transistor of NPN type implemented in an epitaxial layer within a window defined in a thick oxide layer, including: an opening formed substantially at the center of the window, the opening penetrating into the epitaxial layer down to a depth of at least the order of magnitude of the thick oxide layer, the walls of the opening being coated with a layer of silicon oxide and with a layer of silicon nitride, a polysilicon spacer formed on the lateral walls and a portion of the bottom wall of the opening, an N-type highly-doped polysilicon layer formed in the opening and in contact with the epitaxial layer at the bottom of the opening within the space defined by the spacer, an N-type doped region at the bottom of the opening, a first P-type doped base region at the bottom of the opening, a second lightly-doped P-type region on the sides of the opening, and a third highly-doped P-type region formed in the vicinity of the upper part of the opening, this third region being in contact with a P-type doped polysilicon layer, the three P-type regions being contiguous and forming the base of the transistor.