Atomic layer deposition of two-dimensional transition metal dichalcogenides and ovonic threshold switching materials: A new computational framework for precursor design

Different memory concepts are being investigated to enable fast and powerful storage solutions for next generation smart phones, tablets, and pioneering technologies. These include DRAM devices for high-speed access, NAND flash memory devices for storage of large amounts of data, as well as the newly emerging Storage Class Memories (SCM) that promise high-speed for large amounts of data. Each technology requires specific materials. For example, complex chalcogenide thin films are needed to boost the memory cell performance of SCM. The deposition of these materials is challenging, and in this respect Atomic Layer Deposition (ALD) is a promising technique. However, the identification and design of chemical ALD precursors that are compatible with industry-type ALD reactors is not straightforward for complex chalcogenide materials. Understanding the ALD growth mechanisms, the substrate dependency and the impact of precursors is key to engineer the deposition to optimize composition and material properties. A large part of the challenge arises from our inability to forecast the occurrence of dominant chemical reactions in multi-component systems, where thousands to millions of reactions can potentially occur simultaneously, while the thermodynamics of these reactions is unknown for most of the components. This PhD topic aims at solving this challenging issue by using the predictive power of first-principles simulations to build a thermodynamic reference database connecting the thermodynamic properties of new materials, their deposition molecules and their associated by-products. This database will be combined with numerical minimization methods to identify the most likely reactions to occur during material growth and etching. The resulting insights will provide precious information in terms of precursor selection and process control such as concentration, temperature and pressure dependency. As such, the outcome of the simulations will be used to drive the development of new chalcogenide materials and atomic layer deposition processes, and it will be benchmarked against experimental ALD studies.