Thermal stability of Si/Si1−xGex/Si heterojunction bipolar transistor structures grown by limited reaction processing

Abstract

The thermal stability of Si/500-Å-thick Si0.77Ge0.23 bilayers grown on Si by limited reaction processing is studied as a function of Si capping layer thickness. After annealing for 4 min at 850 °C, misfit dislocation spacings increase monotonically with cap thickness from 0.5 μm for an uncapped film to greater than 50 μm for a layer with a 500-Å-thick cap. Thus, an epitaxial Si cap of sufficient thickness prevents significant misfit dislocation formation during this anneal. Experimental observations are reported which indicate that the Si cap enhances thermal stability by inhibiting both dislocation nucleation and propagation. These results are very encouraging since they suggest that high-temperature processing of Si/Si1−xGex device structures may be possible without significant misfit dislocation formation.