Tailoring interfacial oxide for polysilicon bit-cell contacts and emitters with in situ vapor HF interface cleaning and polysilicon deposition in a 4 Mbit BiCMOS fast static RAM

A cluster-tool-based technique for in situ vapor HF cleaning, ultrathin oxide growth and polysilicon deposition is compared to conventional processing in forming polysilicon emitters and polysilicon bit-cell contacts in a 4-Mb/0.5-μm BiCMOS fast static RAM (FSRAM) process. The in situ processing techniques involve removing native oxide with vapor HF, optionally growing several monolayers of thermal interfacial oxide and depositing a polysilicon film using a load-locked multichamber cluster tool. The authors have examined the capability of this process for producing low bit-cell contact resistance while tailoring bipolar gain through the use of a thin interfacial oxide. Results are reported which indicate that the control achieved with cluster tool processing provides greater flexibility in simultaneously optimizing the performance of the polysilicon emitters and bit-cell contacts