Process for making an optimum high gain bandwidth phototransistor structure

Abstract

Abstract THE FABRICATION OF TWO SEMICONDUCTOR STRUCTURES SUCH AS A HIGH SPEED, OPTINUM SENSITIVITY PHOTODIODE AND A MAXIMUM GAIN-BANDWIDTH TRANSISTOR ON THE SAME WAFER IS DESCRIBED. A THIN, LOW RESISTIVITY LAYER IS FORMED ON A HIGHER RESISTIVITY SUBSTRATE AND THE DIODE JUNCTION IS THEN FORMED IN ONE PART OF THE WAFER BY DIFFUSING THE JUNCTIONFORMING REGION THROUGH THE LAYER AND DOWN INTO THE SUBSTRATE. THIS PROVIDES A DIODE OF LOW CAPACITANCE AND OPTIMUM LIGHT SENSITIVITY. THE TRANSISTOR IS THEN FORMED IN ANOTHER PART OF THE SAME WAFER BY FIRST DIFFUSING THE BASE-COLLECTOR JUNCTION INTO THE THIN LAYER FOLLOWED BY A DIFFUSION THEREIN OF THE EMITTER-BASE JUNCTION. THIS DIFFUSION INTO THE LAYER IS VERY SHALLOW AND RESULTS IN A HIGH GAIN-BANDWIDTH TRANSISTOR. THE PHOTODIODE STRUCTURE IS AFFECTED VERY LITTLE BY THE PROCESSING REQUIRED TO FORM THE TRANSISTOR, THUS ALLOWING EACH STRUCTURE TO BE INDEPENDENTLY OPTIMIZED.

Inventors

• 👤 G Weckler

Bibliographic Details