Fabbricazione e caratterizzazione di dispositivi FET per lo studio delle proprietà elettriche di film di MoS2 depositati per ALD

This thesis explores the fabrication of Field Effect Transistors (FETs) using Transition Metal Dichalcogenides (TMDs) like MoS2, which have attracted significant attention due to their exceptional physical, electronic, optical, and chemical properties. These materials hold promise for future applications in photonics, nanoelectronics, ultra-scaled CMOS transistors, and flexible, transparent, wearable electronics. Moreover, TMDs have potential in biomedical applications due to their large surface area, biocompatibility, and versatile chemistry. However, significant challenges remain in synthesizing TMDs with desirable electronic properties on a wafer scale, tuning their properties (e.g., doping), and integrating them into novel electronic devices. This includes reducing contact resistance between metals and TMDs, which is crucial for practical applications. While many research efforts have focused on fabricating devices with single-crystal MoS2 using Electron Beam Lithography (EBL), this method is not scalable for industrial applications. Instead, photolithography, the industry-standard semiconductor fabrication technique, offers higher throughput and scalability. The primary objective of the thesis was to study the photolithography processes necessary for fabricating FETs by depositing patterned Au/Ti contacts on MoS2 samples grown via Atomic Layer Deposition (ALD). An exploratory study was also conducted using Pulsed Laser Annealing (PLA) to improve the Ti/MoS2 interface and reduce contact resistance. PLA uses a KrF excimer laser for ultra-rapid, localized thermal treatment. Various characterization techniques, including Raman spectroscopy and Optical Microscopy, were used to assess the quality of the MoS2 after each fabrication step. Despite fabricating FET devices and measuring the transistor transfer curves, no relevant current was observed, likely due to issues with the Ti/MoS2 interface. PLA was then applied to continuous Ti/MoS2 films, and Atomic Force Microscopy (AFM) and Raman spectroscopy were used to study the morphology and chemistry of the interface. Results showed the formation of a TixSy compound at the interface. Attempts to laser process patterned Ti/MoS2 contacts led to the ablation of Ti due to damage introduced during the metal sputtering phase. In conclusion, the thesis focused on addressing critical challenges in FET fabrication, such as avoiding film delamination and optimizing contact deposition. The optimization of photolithography parameters resulted in good reproducibility, and PLA showed promise in reducing contact resistance without damaging the MoS2 film. These findings suggest potential pathways for improving the performance of TMD-based electronic devices.