Ge instabilities near interfaces in Si/SiGe/Si heterostructures

Compositional characterization of sharp buried interfaces in Si (cap)/SixGe1−x/Si heterostructures is an important topic in SiGe based advanced microelectronics. Extremely high depth resolution is required to detect and optimize near-interface compositional gradients which are crucial for high circuit performance. Here we report on high-resolution, non-destructive interface characterization and near-interface depth profiling by conventional angle resolved photoelectron spectroscopy (ARXPS) and synchrotron radiation photoelectron spectroscopy (SRXPS). We investigated Si/SixGe1−x/Si heterostructures prepared by reduced pressure CVD (RPCVD) characterizing the Ge content at the SixGe1−x interface towards the native SiO2 layer and the influence of additional (1 and 2 nm thick) Si capping layers. For the uncapped samples we found a strong mixing of Ge-oxides and SiOx in the interface region This indicates a high instability of the Ge atoms at those interfaces. Silicon capped (1 and 2 nm) SixGe1−x films are much more stable. They show no Ge-oxide formation at all even after a long-time room temperature storage. We were able to characterize sharp Ge concentration gradients in the vicinity of the Si/SixGe1−x interface with sub-nm resolution and to differentiate between samples containing Ge profile variations within 1 nm. This is important for Ge profile optimization in advanced Si (cap)/SixGe1−x/Si heterostructures