Interfacial Oxide Break-Up in npn Polysilicon Emitter Bipolar Transistors by Fluorine Implantation

A study is made of fluorine implantation into polysilicon for application in npn polysilicon emitter bipolar transistors. Polysilicon sheet resistance measurements are used to monitor the effect of the fluorine on the epitaxial realignment of the polysilicon, and this is correlated with device electrical results. It is shown that the fluorine causes epitaxial realignment of the polysilicon to occur at a significantly lower temperature. In addition, electrical results show that a fluorine dose of 1.5×10¹⁶cm^¿2 causes the base current to rise by a factor of 2.2 compared with unimplanted devices. Both these effects are explained by the action of fluorine in accelerating the break up of the interfacial layer.