Method of fabricating bipolar junction transistor

A method of fabricating a bipolar junction transistor, comprising the steps of:

• forming an isolation structure in a first conductive type substrate;
• forming a second conductive type deep well in the first conductive type substrate to serve as a collector;
• forming a second conductive type well in the first conductive type substrate;
• forming a first conductive type well in the first conductive type substrate to serve as a base;
• forming a buffer region under a portion of the isolation structure and between the base and the second conductive type well, wherein the buffer region and the isolation structure together isolates the base from the second conductive type well;
• forming a second conductive type emitter and a second conductive type collector pick-up region selectively on the surface of the first conductive type substrate;
• and
• forming a first conductive type base pick-up region selectively on the surface of the first conductive type substrate.