A method of forming a bipolar transistor device, and more particularly a
vertical poly-emitter PNP transistor, as part of a BiCMOS type
manufacturing process is disclosed. The formation of the PNP transistor
during a CMOS/DMOS fabrication process requires merely one additional
mask to facilitate formation of a very small emitter in a portion of an
N-type surface layer of a double diffused well (DWELL). Unlike
conventional PNP transistors, a separate mask is not required to
establish the base of the transistor as the transistor base is formed
from a portion of the double diffused well and the DWELL includes a
P-type body layer formed via implantation through the same opening in the
same mask utilized to establish the N-type surface layer of the double
diffused well. The base is also thin thus improving the transistor's
frequency and gain.