Lateral solid phase epitaxy of amorphously grown Si1 − xGex layers on SiO2/Si(100) substrates using in-situ RPCVD postannealing

Lateral solid phase epitaxy (L-SPE) in non-doped or in-situ B-doped amorphous- (a-) SiGe deposited on SiO2 patterned Si(100) wafers by in-situ postannealing in reduced pressure chemical vapor deposition system was investigated for possible heterojunction bipolar transistor (HBT) base link resistivity improvement. Using Si2H6 as Si precursor gas, an epitaxial and amorphous layer was grown on the mask window and on the SiO2 area, respectively. By inserting a-Si buffer underneath, the deposited a-SiGe surface became smoother. After the L-SPE process, an improved L-SPE length was observed due to suppressed random nucleation on SiO2. The L-SPE length increased with increasing postannealing time and saturated due to random poly-grain formation on the SiO2. At the same L-SPE time, increased L-SPE length was observed at higher temperature and at higher Ge concentration. With increasing B concentration in the a-SiGe, the L-SPE length firstly increased. However, after reaching 2 × 1019 atom/cm3, the L-SPE length reduced again down to the undoped case. These results of L-SPE process might have potential to improve dynamic performance of SiGe HBT by reducing the base link resistivity by widening the monocrystalline region around bipolar window.