Tip-Enhanced Raman Spectroscopy and Photoluminescence for Nanoelectronics: Advanced Quality Control of Strained-Silicon Devices and Transition Metal Dichalcogenides Monolayers

Electronic devices and their many and varied integrated circuits components are entangled in modern society so deeply that "nothing can really work without them". This statement led to the relentless demand for enhanced performance, which has driven continuous advancements in nanoelectronics, where scaling down transistor dimensions has triggered unprecedented challenges. With the number of transistors per chip growing exponentially following the Moore’s law to accommodate increasing data processing needs and low production costs, conventional silicon-based technologies are being pushed to their physical limits, especially the Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET), brought already to a critical point for a few years by now, undermined by quantum phenomena and thermal effects, that hinder performance predictability and further scaling. Overcoming these limitations requires new ideas, ranging from the enhancement and upgrade of already employed silicon-based technologies (More Moore), to the exploration of alternative materials to replace transistor parts, up to designs to revolutionize its overall architecture (More than Moore). While these new technologies hold the key to future advances and ensure to accomplish the tasks of the incoming technology nodes, they also pose new hurdles in terms of characterization, particularly regarding the assessment of structural integrity, performance reliability, and fabrication repeatability. This PhD thesis wants to face these challenges and proposes an exceptional answer to the needs of this era of nanoelectronics, which requires precise, real-time observation techniques that can operate in the nanometer domain. This work presents Tip-Enhanced Optical Spectroscopy (TEOS) as a highly effective solution for this demand. TEOS is a cutting-edge technique that comprises Tip-Enhanced Raman Spectroscopy (TERS) and Tip-Enhanced PhotoLuminescence (TEPL), based on the combination of optical spectroscopy and Atomic Force Microscopy (AFM) to provide both chemical and optoelectronic information at nanoscale resolution. By leveraging the high spatial resolution of the AFM, TEOS enables a correlative analysis of material properties, combining chemical and structural composition, morphological features, and optoelectronic behavior in a single, non-destructive process. This unique capability is crucial for real-time quality control in semiconductor manufacturing, particularly as the industry moves toward increasingly complex and miniaturized devices. The experimental section of this work aims to demonstrate the powerful capabilities of TEOS through its application on two prominent technologies proposed to enhance transistors performances: strained-silicon structures and Transition Metal Dichalcogenides (TMDs) monolayers. Strained-silicon, where the silicon crystal lattice is altered through controlled strain distribution, has great potential for improving the efficiency of conventional MOSFETs without requiring significant changes to existing manufacturing fabrication lines. However, achieving consistent strain configurations and detecting structural defects during the production process requires advanced, real-time analysis. Similarly, TMDs single sheets are less than a nanometer thick, thus imposing challenges in verifying their structural integrity and electronic properties, particularly in terms of defect detection, uniformity, and overall material quality. TEOS, with its nanometer-scale resolution and non-invasive nature, provides a robust tool for addressing these challenges, enabling detailed analysis of both strained-silicon and TMDs with unprecedented precision. The thesis is structured to first provide a comprehensive overview of the technological context, beginning with the history of transistor miniaturization and the barriers faced by the semiconductor industry in the Front-End Of Line of integrated circuits to guarantee the requirements of each technology node. It then introduces the concept of optical spectroscopy, both at the micro- and nano-scale, as a viable solution for seeing those structures and devices. A detailed discussion of TEOS is followed by an in-depth exploration of its application to strained-silicon and TMDs. For both the case studies proposed, the thesis will provide a comprehensive explanation of their features, the benefit they offer to semiconductor devices and thus how they can be efficiently characterized envisioning their future large-scale integration. Therefore, the experimental results of each section will highlight the efficacy of multiscale optical spectroscopies as standalone characterization methods. This research is conducted within the framework of the European project Challenges–Real-time nano-CHAracterization reLatEd techNoloGIES, which ran from April 2020 to August 2024. The project aimed to develop versatile non-destructive techniques for in-line multiscale characterization and real-time quality control of semiconductor devices, ensuring their compatibility with industrial production environments like cleanrooms, thanks to the development and testing of plasmonic TEOS tips, characterized by a titanium nitride (TiN) coating. A consistent part of the results of this thesis in fact will concern the TiN probes testing process, which was conducted on the macro-area of samples related to the silicon-based semiconductor industry. Therefore, the research presented here not only contributes to the goals of the single project and the broader European Chips Act, but also paves the way for the integration of Tip-Enhanced Optical Spectroscopy into standard semiconductor manufacturing processes, ensuring that the next wave of technological innovation is built on a solid foundation of detailed material understanding and quality control.