Atmospheric Pressure CVD-Grown SiGe Base, Polysilicon-Emitter Heterojunction Bipolar Transistor

Using an commercially available atmospheric pressure chemical vapor deposition (APCVD), n-p-n Si/SiGe/Si heterojunction bipolar transistors (HBTs) with arsenic-implanted polysilicon-emitter, which is isolated by polysilicon-filled trench and LOCOS, has been fabricated. At atmospheric pressure, Si/SiGe bilayer was deposited using SiH4-based process on the LOCOS-patterned wafer. Mole fraction of Ge in the SiGe base was linearly graded from 0 at the emitter side to either 0.15 or 0.2 at the collector side. Regarding the trade-off between common-emitter current gain (ß) and Early voltage (Va) as well as cutoff frequency (fT) and collector-emitter breakdown voltage (BVceo), device was designed for the optimal performance. Titanium silicide (TiSi2) layer is used as a base electrode instead of the doped polysilicon. In addition, in order to achieve more complete activation of arsenic dopant in polysilicon-emitter and simultaneously suppress boron outdiffusion from the SiGe base to the adjacent Si, condition of the thermal annealing to drive-in the arsenic dopant was compromised to be the combination of furnace annealing at 840°C for 20 minutes and rapid thermal annealing at either 900 or 950°C for 20 seconds. The Si/Si0.85Ge0-0.15/ /Si HBT with the mask size of 1×4¿m² emitter typically shows nearly flat ß of 118, Early voltage of 60, BVceo of 7.0V, and fT peak at 25GHz, while Si/Si0.8Ge0-0.2/Si HBT exhibits ß peak at 2000, Va of 100V, BVceo of 5.5V, and fT peak at 27GHz. To author´s knowledge, the value of ß*Va of our device is highest among the reported data.