Micro­struc­turing Large Sur­fa­ces with a UV Laser

Annealing of silicon has contributed greatly to the renaissance of excimer lasers. Now, researchers are considering what other materials might be suitable for this method. (Source: Coherent)

In the last few years, the rapid growth in display manufacture for mobile devices has ushered in a considerable renaissance for excimer lasers. Operating in the UV range, they allow precise modification of silicon as well as ablation of ultra-thin polymer layers using the laser lift-off process. However, the potential applications of this laser technology are far from exhausted.

In a collaborative project spanning several years, Coherent and Fraunhofer ILT plan to develop novel procedures with the excimer laser. To this end, Coherent has provided an ILT research team with a line beam system.

The system’s laser line is 155 mm long, 0.3 mm wide, and its stabilized UV output is more than 150 W at 248 nm. A masked imaging system can also be connected, if required. Each laser pulse can reach an energy of more than 1 J, allowing both removal of various materials at a micrometer resolution and rapid, selective processing of layer systems in the micro- and nanometer range. “No other system can match this combination of precision and processing speed,” says Ralph Delmdahl, product marketing manager for Coherent.

Handover of the Coherent system LineBeam 155 to Fraunhofer ILT (from left): Christian Hördemann, ILT, Thorsten Geuking and Rainer Pätzel, Coherent, Arnold Gillner, ILT, and Ralph Delmdahl, Coherent. (Source: Fh. ILT / A. Steindl)

“Our goal is to qualify new applications and new materials that can be subsequently scaled up for industrial production,” explains Arnold Gillner, head of ablation and joining at Fraunhofer ILT. One of the first areas of focus is processing of fiber composites. The excimer laser, for instance, can be employed for carefully controlled and precise preparation of carbon fiber reinforced plastic (CFRP) adhesive surfaces. Another application is large-surface removal of release layers in the production of CFRP components. This might have as much potential in aviation as it has in shipbuilding. Targeted modification of surfaces is a further goal of the cooperation. Such modification provides technical components with additional functionalities, which could otherwise be manufactured only with the aid of expensive coatings.

Crucially, the low penetration depth of the UV radiation enables the surface to be functionalized at the same time as maintaining a very low heat input. This makes the excimer laser, due to its very short wavelength, superior even to new ultrashort pulse lasers. The potential applications are extremely diverse. In addition to evaluating procedures for processing strategies, the laser can also be used to investigate novel materials for their machinability. One possible application is the efficient production and modification of nanoscale graphene layers, in which the short wavelength of 248 nm – and the associated high photon energy – plays a decisive role.

Research projects like these indicate that Coherent and Fraunhofer ILT are looking to the long-term in their collaboration. Both partners can use the system jointly with their customers for projects. This provides small and medium-sized companies with a potential technological basis to develop new products with innovative functionalities. (Source: Fh. ILT)

Links: Fraunhofer Institute for Laser Technology ILT, Aachen, Germany • Coherent, Inc., Santa Clara, California, USA

Further reading: R.  Delmdahl & V. Pfeufer: UV Lasers Enable Smart Phones and Other Microelectronics, Laser Technik Journal, online 30. December 2010; DOI: 10.1002/latj.201090107 • R. Delmdahl: Fabricating the Flexible Future, Optik & Photonik, online 16. December 2016; DOI 10.1002/opph.201600039 • Interview: Flexible Display Manufacturing by the Meter, photonicsvies.com, 17 June 2016

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