A Base-Collector Architecture for SiGe HBTs using Low-Temperature CVD Epitaxy Combined with Chemical-Mechanical Polishing

Abstract

A new collector technology intended for an integrated high-speed SiGe heterojunction bipolar transistor (HBT) is reported. The collector was fabricated by selective epitaxial growth (SEG) using chemical vapor deposition at 770°C under reduced pressure (20 torr) using SiH2Cl2 as silicon precursor and PH3 as n-type dopant source. Chemical-mechanical polishing (CMP) was applied to the overgrown SEG collector in order to achieve a smooth surface in level with the surrounding oxide. Finally, a SiGe base doped with boron was deposited using non-selective epitaxial growth (NSEG) at 650°C. The topography of the collector is inspected after each process step by atomic force microscopy and the topography of the completed collector/base stack indicates that this structure is promising for fabrication of the emitter window. A further advantage with the CMP procedure is the elimination of phosphorous segregation as evidenced by secondary ion mass spectroscopy of the base-collector stack.