HiPIMS-CVD Hybrid Process for Advanced Functional Coatings: Proof of concept

Magnetron sputtering is a physical vapour deposition (PVD) process extensively used in industry for the deposition of functional coatings for many applications. Although the process is able to deposit a wide range of functional materials including many oxides, nitrides and metals in complex multi-layer stacks with exceptional uniformity over large areas, deposition rates are relatively low, making the deposition of certain materials or products uneconomical. In addition, there are still some commercially important materials, such as aluminium oxide, which can cause severe processing instabilities (i.e. arcing, loss of anode surfaces, creation of negative ions, etc.), which restricts their usage. Plasma enhanced chemical vapour deposition (PECVD) is a competing process in which gaseous precursors form solid deposits on the substrate through reactions driven by energetic particles from the plasma. PECVD processes generally have the advantage of very high deposition rates, high conformity and low roughness, but are limited, largely by the available precursors, in the range of materials and complexity of the stacks that can be deposited. There are also limitations in uniformity over large area substrates.

In order to reduce product cost and improve performance, there is a demand to improve upon the rate and, where applicable, the stability of the sputtering process and a similar demand for improving/expanding the material choice and uniformity of the PECVD process to open up new applications. An alternative means of achieving these goals is to combine the technologies simultaneously. This academic/industrial collaborative project is designed, therefore, to develop new hybrid deposition processes, combining the latest magnetron sputtering technologies with PECVD technologies for the high rate deposition of enhanced functional films, which are capable of scale-up and integration into existing large area inline deposition facilities to provide a new improved route to production, ideally at low temperature. The innovative approach taken here will be to use the HiPIMS (high power impulse magnetron sputtering) power delivery mode to drive both the magnetron and the CVD process. This is the first time that HiPIMS will have been used in this environment and this proposal is designed to act as a 'proof of concept' project. HIPIMS involves the application of very large power pulses to magnetron sputter cathodes for short periods. These intense pulses create high plasma densities, leading to a high degree of ionization of the sputtered species. The flux of coating material to the substrate can then be controlled by varying the magnetic field strength of the magnetron. Thus, adjustment of the magnetic array allows a means of controlling the flux of sputtered metal dopant to the growing CVD film, whilst still operating at the same pressure and time averaged power and, therefore, still maintaining the same plasma density in the process zone.

The primary deliverable from this project will, therefore, be the development of a new method for the synthesis of functional films. This method will be validated through the deposition of carefully selected functional films relevant to industry and the characterisation of the deposition process.

In this proof of concept project, we will develop a novel, hybrid deposition system for the manufacture of high quality functional films that addresses the issues of low deposition rates in magnetron sputtering systems and limited materials choices in CVD systems. The new system will be validated through the deposition of carefully selected functional films relevant to industry and the characterisation of the deposition process. This, in turn, will provide a set of operating protocols to inform scale-up and future development of the process. Collectively, the outputs of this project will generate routes to impact in academia, industry and society, as described below.

Academic Impact: We will disseminate our findings relating to the deposition of metal oxide and nitride thin films by the HiP-CVD process in the scientific literature and at international meetings. Publications will be targeted at appropriate high quality peer-reviewed journals and presentations will be made at leading national meetings and international conferences. Information will also be widely disseminated throughout the UK PVD and CVD networks. The individual research groups will maintain their web presence to publicise this project, which will include video clips of laboratory experiments and interviews with researchers.

Industrial Impact: The project seeks to develop new methodology with significant impact in a number of innovation sectors that use PVD/CVD technology. Following the successful demonstration of our concept, we will collaborate with our industrial partners (Pilkington Technology Management, Teer Coatings Ltd., Emerson and Renwick and Gencoa Ltd.) to seek follow-up funding (e.g. Innovate UK, EPSRC - Manufacturing the Future) to enable technology transfer as a route to new product and process development. Their expertise in applied R&D of coated products, industrial-scale processing and bespoke production systems will be a crucial element in bringing the deliverables from this project to market and raising UK competitiveness in the manufacturing of functional films. As the project progresses and in follow-up projects, there may be opportunities for other companies to become involved and collaborate. This might include end users of PVD and CVD technology (e.g. Centre for Product Innovation, Guardian Glass, Pegasus Chemicals, EpiValence and Oxford Applied Instruments), and plasma diagnostics manufacturers (e.g. Hiden Analytical and Impedans). An IP exploitation strategy will be agreed before the project commences.

Societal Impact: The project will provide "world-class" academic challenges and an opportunity for the researchers to develop into future scientific leaders. This will benefit UK science in general by strengthening its research base, and bringing forward new talent. The PDRA and Research Fellow will develop managerial skills, commercial and IP awareness through continuing professional development training (CPD) courses, such as time management and advanced communication skills.

The importance of public engagement has also been recognised with the publication of the RCUK Concordat for Public Engagement (PE). Our research programme offers an opportunity to engage with the public in demonstrating the key position of the physical sciences to our society.