Abrupt SiGe-to-Si interface: influence of chemical vapor deposition processes and characterization by different metrology techniques

Future electronic (gate-all-around transistors) and photonic devices (electro-absorption modulator and laser stack) will require SiGe/Si multilayer stacks with abrupt interfaces. Chemical vapor deposition (CVD) is a proven method to epitaxially grow such multilayer structures. However, the abruptness of the compositional change is limited by Ge segregation occurring during Si layer growth on a (Si)Ge surface. Here, we study the compositional abruptness at the interface between Si_0.70Ge_0.30 and Si layers epitaxially grown in a CVD reactor. The ultra-thin interface layer between SiGe and Si is characterized by transmission electron microscopy, secondary ion mass spectrometry and spectroscopic ellipsometry (SE). Our results show that a Si layer grown using a chlorinated chemistry produces the most abrupt interface. For Si deposition processes with non-chlorinated chemistry, lower growth temperature and a higher order hydride precursor result in a reduced transition thickness. Furthermore, we show that the interface thickness measured by the different metrology techniques are in good agreement, suggesting that SE can be used to evaluate the ultra-thin interface at the Si_0.70Ge_0.30-to-Si interface, resulting in considerably shorter development time in a production environment. (paper)