Patent ID: 6400542
Filing Date: 2002-06-04
Classification: H01L

Abstract:
A method of forming a voltage clamping circuit comprising a group of Darlington connected clamping transistors on a semiconductor substrate, comprising the steps of:providing the semiconductor substrate; diffusing a material of a first impurity to a first concentration into the surface of the semiconductor substrate to form a collector well for each of said group of clamping transistors; diffusing the material of the first impurity to a second concentration into the surface of the semiconductor substrate within each collector well to form at least one collector contact that is a first low resistivity connection to each collector well; diffusing a material of a second impurity to a third concentration into the surface of the semiconductor substrate within each collector well to form a base well for each clamping transistor of the group of clamping transistors; diffusing the material of the second impurity to a fourth concentration into the surface of the semiconductor substrate within each base well to form a base contact that is a second low resistivity connection to each base well; diffusing the material of the first impurity to the second concentration into the surface of the semiconductor substrate within each base well to form an emitter contact for each clamping transistor of the group of clamping transistors; connecting a first power supply voltage terminal to all collector contacts of the group of clamping transistors, connecting the first power supply voltage terminal to the base contact of a first clamping transistor of the group of clamping transistors, connecting the emitter contact of the first clamping transistor to the base contact of a subsequent adjacent clamping transistor, connecting the emitter contact of each subsequent clamping transistor to the base contact of a following subsequent clamping transistor; and connecting the emitter contact of a last clamping transistor to a second power supply voltage terminal.