Process Improvements in the Selective Epitaxial Growth of Si1 − xGex / Si Strained Layers in a Conventional Hot‐Wall LPCVD System

Abstract

Three process considerations were identified as essential for the selective epitaxial growth (SEG) of SiGe in hot‐wall tubular low pressure chemical vapor deposition reactors. A thermodynamic analysis of the system 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 hydrogen bake was developed to eliminate the problem. A high temperature bake, carried out before wafer loading, removed residual Ge deposited on the reactor wall from the previous run. After wafer loading, removed residual Ge deposited on the reactor wall from the previous run. After wafer loading and purge, a lower temperature bake then removed the native oxide. Second, a selectively grown Si buffer layer improved the initial growth surface for later SiGe SEG. The Si buffer layer covered the remaining native oxide, which the previous hydrogen bake did not totally remove, and reduced the defects at the interface. Finally, a small flow of Si source gas during the temperature ramp down period helped to keep the buffer layer surface clean prior to SiGe SEG. All three steps proved to be essential in obtaining SiGe SEG of higher quality.