Direct Writing of Nanodevices: A Sustainable Route to Nanofabrication

This research project, funded by UKRI (Engineering and Physical Sciences Research Council), commenced in May 2023 and coincided with the publication of the UK’s first National Semiconductor Strategy.

The ability to write structures at the nanoscale using lithography underpins modern society. The electronic devices we take for granted contain integrated circuits (ICs), and the key component of those circuits are field-effect transistors (FETs). They have reduced in size by a factor of two every two years for over forty years, following "Moore's Law". The roadmap for the electronics industry now assumes that this constant reduction of size will continue - at least until the mid-2020s. At the end of 2019, Extreme ultraviolet lithography (EUVL) began to be used to manufacture FinFETs (i.e. FETs that resemble a Fin) as part of ICs at the 7 nm node. Unfortunately, EUVL has an astronomical cost, where each tool costs > $100 M dollars with similarly costs for maintenance. It is evident that this is a colossal investment for larger' semiconductor manufacturers i.e. Intel, TSMC, Samsung, Global Foundries, Infineon, LG. The cost is not sustainable which has led the International Technology Roadmap for Semiconductors (ITRS) to declare that it will no longer be economically feasible to decrease FET device dimensions past the 5 nm node. This has led to significant uncertainty in the future direction of the semiconductor industry, especially for smaller manufacturers that risk being priced out of the market. Additionally, lithography is a subtractive process and very energy demanding. Layers are added in manufacture that are then largely etched away during fabrication. This is wasteful and more sustainable processes are needed moving forward. Equally, plasma etching for the step where the lithographed structure is transferred into the substrate (silicon or compound semiconductor) uses a large amount of energy. If we could directly write structures we would use less precursor, produce less waste and reduce energy consumption and potentially make the process sustainable as well as accessible for smaller manufacturers.

The project objective is to demonstrate a new sustainable and relatively inexpensive manufacturing process that will allow less waste and reduce energy consumption and potentially make the process sustainable as well as accessible for smaller manufacturers in the UK and beyond. This new manufacturing technique is based on the decomposition of molecular precursor molecules in ion beams. As these precursors have preformed metal-chalcogen bonds they decompose in the ion beam directly to useful semiconductors such as metal oxides and metal sulfides, with written pattern resolutions beyond the 7 nm node, at a fraction of the time and processing cost compared to extant processes in the semiconductor industry. The project will demonstrate that a number of useful nanoscale devices for (i) thermoelectric energy generation (ii) single photon detection above 77K and (iii) logic circuits for 16 bit memory can be prepared in this way, written at resolutions beyond what is currently possible to most small semiconductor businesses in the UK.