Application of base drift field measurement to processing optimization of advanced bipolar transistors

A technique for directly measuring the base drift field in bipolar transistors has been developed and used to study the effects of various base-formation and emitter drive-in conditions on the effective base drift field, a major factor determining the unity-current-gain cutoff frequency f_T, has been studied. Measurements of base drift fields created with these drive-in conditions revealed that insufficient thermal treatment leaves a large portion of the base region with a retarding field, producing low base drift fields and low f _T´s. An appropriate thermal treatment creates a monotonically varying base profile with large drift fields and therefore high f_T´s