An ultra-shallow link base for a double polysilicon bipolar transistor

A techinque is presented for forming an ultrashallow link base in a double polysilicon bipolar transistor. This method is easily integrated into an advanced BiCMOS process, making use of a disposable polysilicon spacer technology for MOSFET lightly doped drain (LDD) formation. It makes use of the diffusion of boron from a disposable polysilicon spacer, through a thin thermal oxide layer to the underlying silicon. A very shallow link base is thus formed, allowing independent optimization of the active and link base regions. This improves the trade-off between base-emitter breakdown and base resistance and results in improved bipolar performance.<>