Bipolar transistor manufacturing method

A method of manufacturing a bipolar transistor in a substrate of a first conductivity type, including the steps of:

• forming in the substrate a first area of a second conductivity type;
• forming by epitaxy a first silicon layer;
• forming in this first silicon layer, and substantially above the first area, a second heavily-doped area, of the first conductivity type;
• forming at the periphery of this second area a third area of the second conductivity type separate from the second area;
• forming by epitaxy a second silicon layer;
• forming a deep trench crossing the first and second silicon layers, penetrating into the substrate and laterally separating the second area from the third area;
• and
• performing an anneal such that the dopant of the third area is in continuous with that of the first area.