Metrology for highly-parallel manufacturing

To increase European competitiveness industry is turning to highly-parallel manufacturing (HPM). HPM can reduce the cost of goods by applying traditional methods such as roll-to-roll (R2R) embossing and injection moulding to modern, large area devices. These include flexible photovoltaics, smart packaging and printed electronics. The latter sector alone has been predicted to generate €262 bn by 2027 if underpinned by investment.

HPM products may be composed of multiple layers of different materials containing nanometre-sized features, each requiring precise positioning or ‘registration’ for reliable performance. To ensure items are free from defects and imperfections manufacturers need quality checks at multiple stages of the production process. Prior to this project, stakeholders in the R2R sector stated that an overlay accuracy of ±  20 m was the target required for promoting this technology but the state of the art at the time was ± 50 μm. Furthermore, to increase competitiveness measurements must be cost effective, high-speed and accurate. Optical measurement techniques had the potential to meet these requirements but were limited due to measurement instrument sensitivity to surface features. New technologies had the potential to overcome this but lacked the calibration standards and methodologies to validate their use in modern production lines.

This project improved inspection measurements for HPM by tackling key gaps in metrology capabilities. For 2D and 3D surface analysis new instrumentation was developed including a portable spectroscopic scatterometer and a hybrid 2D/3D inspection platform. The scatterometer enables real time feedback on nanostructured surfaces and the hybrid inspection platform is capable of measuring surface structures and defects on large area substrates with a high dynamic range and resolution. Two systems were designed to obtain highly accurate 3D measurements from inexpensively acquired image data. The first, a ptychographic sensor, uses optimised algorithms to give traceable measurements of surface structures at high-resolution and the second is a general concept for an all-optical sensor based on novel filtering optics. Systems for in-line monitoring of multi-layered printing technologies were also developed, including new registration technology allowing below 5 μm accuracy in substrate position measurements and new substrate handling mechanisms resulting in a fivefold improvement in registration, with ± 20 μm level registration accuracy. A prototype encoder system was developed to provide feedback during production which enabled steering control, at speeds of up to 15 m per minute, on a 1.4 m width R2R production research platform.

Through a set of key HPM test cases new practical tools, techniques and good practice was developed to enable HPM users to efficiently quantify correlations between a surface’s performance (such as photovoltaic efficiency) and its 3D topography and to exploit this correlation for smarter in-process measurement and real-time process feedback. The new methodology has already been used in European manufacturing and will continue to increase the efficiency and quality of production processes and reduce the costs of high value products by applying an ‘economy of scale’, allowing industry a competitive edge in this emerging field.