Nanoscale characterization of PMMA residues and plasma damage on transition metal dichalcogenides

This thesis focuses on investigating defect generation and healing in processed transition metal dichalcogenide (TMD)-based two-dimensional (2D) materials using advanced scanning probe microscopy (SPM) techniques sensitive to local topographical, mechanical, and electrical properties. These 2D semiconductors have the potential to complement silicon as channel materials in advanced CMOS devices. Different research groups and chip manifacturers are researching and considering their use in efficient 2D transistors as another step in the transistor shape evolution after finFET and GAA, to overcome present limitations and allow further node shrinking. This includes Imec, that has inserted those type of materials in their logic technology roadmap. Currently, two interrelated challenges hinder their integration: (1) limited fundamental understanding of defect control during growth and processing and (2) the need for reliable material characterization. This project addresses one critical fabrication step - plasma interaction with the processed 2D layer - and develops a rigorous methodology to enable subsequent in-depth evaluation of material property. The need for developing such a methodology, identified as a key challenge, arises from the formation of a high-density, ultra-thin (1–4 nm) polymer residue at the 2D interface after TMD substrate transfer, which prevents direct probing of the material. Preliminary studies have shown that applying local mechanical pressure with an atomic force microscopy (AFM) tip can partially remove this layer, but its effectiveness and influence on the underlying 2D material remain unclear. To address this, two different aspects will be studied and optimized in this work: the process of controlled material at the region of interest and the assessment of local current transport using conductive AFM or complementary electrical modes and changes in nanomechanical properties through quantitative nanomechanical mode AFM.