Investigation of Arsenic Transient Enhanced Diffusion From Emitter Process at 550 °C Si:As RP-CVD Epitaxy Using Disilane Precursor

Emitter resistivity should be optimized to increase the electrical performances of bipolar transistors. A non-selective Si:As deposition at temperature higher than 600 °C is currently used to fabricate such emitters: poly Si:As grows on dielectrics whereas monocrystalline Si:As grows on Si. A fully monocrystalline material would be needed to reduce the emitter resistivity, however. Therefore, a new process performed at 550 °C has been developed with Si 2 H 6 as the Si precursor. Emitter mono-crystallinity is achieved by coupling amorphous deposition on dielectrics and solid phase epitaxy regrowth. The crystallinity of the structure has been checked by ACOM-TEM. With the Si 2 H 6 process, an unusual diffusion of As is observed and has been reproduced on blanket wafers. The study on blankets wafer highlights that the diffusion is enhanced during a period: no enhanced diffusion occurs between 10 h and 24 h annealing at 720 °C. For the first time, transient enhanced diffusion of As is observed after low temperature epitaxy.