Manufacturing with Light 2: photochemical ALD to manufacture functional thin films

The purpose of this project is to develop a novel photochemical atomic layer deposition (ALD) manufacturing technology to coat three - dimensional components and feedstock powders with ultrathin functional coatings. Conventional atomic layer deposition is already widely used in the displays and microelectronics industries. It is a thermo-chemical process where two precursor reagents are pulsed in cycles onto a heated work piece. The combination of the substrate temperature and the chemical reaction energy drive the process forward to deposit the thin film layer by layer. Because the process occurs on the surface, highly uniform and conformal layers can be deposited onto high-aspect ratio or porous materials with ultraprecise thickness control. The hypothesis for the proposed research is to use a photo-excitation process to activate one or both of the ALD chemical reagents so that they can react to deposit the thin film with a lower thermal input from a substrate heater.

We will adapt the existing Round 1 ALD reactor at Liverpool to incorporate a larger scale chamber capable of containing: (1) an array of 3D components; and (2) reactor furniture for a fluidised bed powder treatment system. The modified system will be built to accommodate ultraviolet sources for the processing of 3D components or the treatment of powder beds. We also propose to use new UV source lamps to target the wavelength of the output from a range of commercially available UV lamp modules to photo-chemically decompose the precursors to form the film. The replacement chamber will also be manufactured to enable access for in-situ monitoring of the deposition process using an existing fibre-optic cable based Raman probe and a quartz crystal microbalance. These will provide feedback on the start of deposition as a function of illumination, substrate temperature, flow rates etc. If achieved, these objectives represent a significant advancement of existing ALD technology and would open up new applications where ultrathin functional materials can be exploited, such as display electronics, biomedical devices and photovoltaics amongst others.

This project will have direct impact on the world-wide research and development of ALD technology. The development of ALD manufacturing technology has been driven by advancements in the IC electronics sector over the last decade. The global ALD market is $0.5bn and is forecast to reach $1.8bn by 2016 [1]. This comprises 40% of materials and 60% of equipment sales. The current trend is now to diversify across other manufacturing sectors. The proposed project will
make a significant contribution to enabling ultrathin film manufacturing by enabling direct-write patterning and lower temperature processing.

The industry collaborators for the proposed program have clear and direct opportunities to exploit the arising research. One of our industrial collaborators Pegasus Chemicals has recently been established and specialises in the manufacturer of precursor materials for chemical vapour deposition and atomic layer deposition. The company has extensive experience in the design, selection and delivery of organometallic precursors and we will work with them to develop photochemically active sources for the research proposed here. The Liverpool University group has had a long-term collaboration with researchers in the company which will help us to accelerate the route to impact. The research has the potential to put the UK at the forefront of a crucial emerging area of new materials and precursors, which is likely to impact strategically on the UK and European economy. Nanoco is unique in the nanomaterials market as a company that manufacture large quantities of quantum dots to develop a wide variety of next-generation products, particularly in the fields of electronics, lighting, biomedical and PV solar cells. Renishaw is a global company with core manufacturing competences encompassing laser melting, vacuum casting and injection moulding technologies. Renishaw's laser melting process is an emerging manufacturing technology with a presence in the medical orthopaedics industry as well as the aerospace and high technology engineering and electronics sectors. Renishaw also sells a range of materials and consumables to support their vacuum casting, laser melting and low-volume production technologies. These included advanced powder materials of the type that we propose to develop further within this project.

[1] Annina Titoff, Editor in Chief "ALD Pulse" (2013)