Manufacturing process of bipolar IC with Zener diode

This paper describes a manufacturing process of a bipolar IC with a Zener diode. The Zener diode is manufactured by a process which is compatible with the ordinary bipolar IC process. Since the breakdown voltage of the Zener diode is not equal to the emitter-base breakdown voltage of the longitudinal n-p-n transistors, the doping concentration in the positive area of the Zener diode is not the same as the doping concentration in the base area of the n-p-n transistor. The doping concentration and junction depth of the positive of the Zener diode is decided by its breakdown voltage value. It is produced by another implantation dose and followed by a drive-in step. Hence this process utilizes two boron implantations during the base area formation, one is used to form the base area of ordinary n-p-n transistors, another is used to make the positive of the Zener diode. The relationship between the implantation dose and breakdown voltage of the Zener diode is investigated. A bipolar ASIC with a Zener diode was fabricated by this process.