Increased current gain and reduced emitter resistance in F-implanted, low thermal budget polysilicon emitters for SiGe HBTs

Low thermal budget polysilicon emitter contacts are reported for application in SiGe HBT processes. A fluorine implant into the polysilicon is shown to enhance the breakup of the interfacial oxide layer, and to significantly reduce the emitter resistance, when combined with anneals compatible with the fabrication of SiGe HBTs. If is shown using TEM that a 5×10¹⁵ cm^-2 fluorine implant, combined with an interface anneal of 30 seconds at 950°C prior to emitter implant, and an emitter drive-in of 30 seconds at 900°C, produces devices with a broken interfacial oxide layer. Similar control devices which did not receive a fluorine implant showed no signs of interfacial oxide break up. Emitter resistance measurements show that the specific interfacial resistivity falls from 114 for the control device to 17 Ω μm² for the device implanted with fluorine. Finally processing conditions are identified that allow low emitter resistance to be combined with a suppression of the base current