PROCESS IMPROVEMENTS IN THE SELECTIVE EPITAXIAL-GROWTH OF SI1-XGEX SISTRAINED LAYERS IN A CONVENTIONAL HOT-WALL LPCVD SYSTEM/

Three process considerations were identified as essential for the sele ctive epitaxial growth (SEG) of SiGe in hot-wall tubular low pressure chemical vapor deposition reactors. A thermodynamic analysis of the sy stem revealed that the hydrogen bake condition for SiGe SEG had to be modified from that for Si SEG to eliminate outgassing of residual Ge, which adversely affected the initial growth surface. A two-step hydrog en bake was developed to eliminate the problem. A high temperature bak e, carried out before wafer loading, removed residual Ge deposited on the reactor wall from the previous run. After wafer loading, removed r esidual Ge deposited on the reactor wall from the previous run. After wafer loading and N-2 purge, a lower temperature bake then removed the native oxide. Second, a selectively grown Si buffer layer improved th e initial growth surface for later SiGe SEG. The Si buffer layer cover ed the remaining native oxide, which the previous hydrogen bake did no t totally remove, and reduced the defects at the interface. Finally, a small flow of Si source gas during the temperature ramp down period h elped to keep the buffer layer surface clean prior to SiGe SEG. All th ree steps proved to be essential in obtaining SiGe SEG of higher quali ty.