Method of making a saturation-limited bipolar transistor device

Abstract

A saturation-limited bipolar transistor device or circuit and a method of making same are provided which includes a merged NPN transistor and a PNP transistor structure formed so as to produce denser cells or circuits. A simple process is used to form the structure which includes a double diffused technique for making the PNP transistor. The PNP transistor has a double diffused emitter-base arrangement wherein the emitter is asymmetrically positioned with respect to the base so as to also serve as a contact for the base of the NPN transistor. The PNP transistor limits the input current by bypassing excess current to a silicon semiconductor substrate or chip. The structure includes an N type epitaxial layer formed on an N type subcollector with a P type region provided near the surface of the epitaxial layer. The epitaxial layer serves as the NPN collector and as the PNP base contact region. A first N type region is formed through the P type region extending from the surface of the epitaxial layer to the subcollector dividing the P type region into first and second sections which serve as the PNP collector region and the NPN base region, respectively. A second N type region is formed in the second section of the P type region at the surface of the epitaxial layer acting as the NPN emitter and a P+ region is formed in the first N type region at the surface of the epitaxial layer extending into the second section of the P type region which forms the NPN transistor base. This P+ region serves as the PNP emitter and as the NPN base contact.