Defect Assessment, Control and Engineering in Advanced Homo- and Hetero-Epitaxial Device Structures (Defect beoordeling, controle en engineering in geavanceerde homo- en hetero-epitaxiale device structuren)

In advanced CMOS technology nodes, new channel materials and/or efficient methods to create strained channels are recognized as powerful techniques to boost the performance of both nMOS and pMOS transistors. However, a major concern is that in most of the cases, there is some lattice mismatch between the substrate and the epitaxial layer resulting in the formation of extended defects (dislocations) beyond the critical heteroepitaxial thickness. The occurrence of extended defects and the presence of a narrow bandgap semiconductor can boost the MOS transistor leakage in the sub-threshold region or IOFF state leakage, through the drain-substrate junction leakage. That would produce an undesired increase of the power consumption. Hence, to achieve an efficient optimization it is important to keep a good junction control with an acceptable leakage level.This thesis focuses on the stress analysis and defect characterization techniques of SiGe/Si and Ge/Si hetero-epitaxial device structures. The epitaxial layer quality and the presence of electrically active defects present in the studied hetero-structures, which could significantly degrade the mobility enhancement and affect the trap response at device level in advanced MOS transistors, are studied in detail.Moreover, the impact of high electric fields, present in advanced CMOS technologies, and the influence of mechanical stress and extended defects on junction characteristics are evaluated. It is shown that the carrier transport of advanced hetero-junctions is mainly influenced through the impact on semiconductor lifetimes, bandgap, effective mass and trap level parameters. Additionally, the impact of hetero-interface related effects such as band discontinuities and interface states are also discussed. The experimental data from the electrical analysis have been complemented by stress metrology and characterization techniques such as stress analysis by the laser reflectance technique, high resolution X-Ray Diffraction, Raman spectroscopy, and the nano-beam diffraction technique. The properties of electrically active defects were evaluated by spectroscopic and structural analysis techniques e.g. Deep Level Transient Spectroscopy (DLTS) analysis and Transmission Electron Microscopy (TEM) techniques. Moreover, process and electrical simulations are employed, providing a deeper and fundamental insight in the underlying device physics.In this thesis work, it is demonstrated that the epitaxial quality of advanced materials can be accurately evaluated based on a detailed analysis of junction characteristics, whereby an improved physical understanding of the high doping density and hetero-interface effects on the carrier transport is obtained.Based on the results, a methodology is developed to correlate the current-voltage (I-V) and capacitance-voltage (C-V) characteristics in advanced materials with the physical parameters that affect its behavior. Using this methodology, other advanced hetero-epitaxial structures based on III-V semiconductor materials may be evaluated, allowing to define optimal design rules for a good defect control.status: publishe