A SUBCOLLECTOR WINDOW IS OPENED IN AN OXIDE COVERED P- SIALICON SUBSTRATE. TWO N DOPANTS OF DIFFERENT DIFFUSION RATES (ARSENIC AND PHOSPHOROUS) ARE DIFFUSED THROUGH THE WINDOW INTO THE SUBSTRATE. THE OXIDE COVERING IS REMOVED AND A P- SILICON EPITAXIAL LAYER IS DEPOSITED ON THE SUBSTRATE AND REOXIDIZED. DURING THE REOXIDATION CYCLE, THE PHSOPHOROUS AND ARSENIC ARE OUT-DIFFUSED, THE PHOSPHORUS REACHING THE TOP SURFACE OF THE EPITAXIAL LAYER TO PRODUCE AN N POCKET IN THE P- EPITAXIAL LAYER AND SUBSTRATE, THE POCKET HAVING A HEAVILY DOPED N+ REGION ADJACENT THE

EPITAXIAL LAYER-SUBSTRATE INTERFACE. BASE AND EMITTER DIFFUSIONS ARE MADE WITHIN THE N POCKET TO FORM A TRANSISTOR.