A true polysilicon emitter transistor

A polysilicon emitter transistor has been fabricated in which the metallurgical base/emitter junction coincides with the interface between polycrystalline and monocrystalline material. The emitter region was formed by deposition of heavily phosphorus-doped polysilicon in an LPCVD reactor at 627°C, a temperature low enough to prevent diffusion of phosphorus into the substrate. Emitter Gummel numbers of over 10
¹⁴
scm
^-4
have been obtained with this structure, allowing common emitter current gains in excess of 10000 to be reached for base implant doses of 10
¹²
cm
^-2
.