Thin films are powerful tools for improving performance and increasing the scope of technical components in many areas of modern life. In many cases thin film processing is a 2-step process involving film deposition (e.g. inkjet, screen printing) followed by heat treatment to obtain the required film functionality. This heat treatment in many cases is essential for crystallization, annealing, drying or sintering of the film material using temperatures that exceed the temperature stability point of the substrate. Laser treatment overcomes this drawback by virtue of its rapid heating and cooling rates.
The absorption of laser radiation in thin films rises with increasing film thickness resulting in higher film temperatures. In consequence irregularities of film thicknesses (caused by an unstable printing process) can lead to either insufficient functionalization or damage to the film whilst using constant laser process parameters. Thus process monitoring and controlling of laser-based thin film treatment are indispensable in order to evaluate the process quality and to evenly functionalize thin films.
The Fraunhofer ILT is developing process monitoring and control for laser treatment of inkjet-printed nano-particulate ITO films (see Figure 2). Printed sheet resistances of several hundred kΩ/sq can be evenly reduced to less than 200Ω/sq (>3 orders of magnitude) using the controlled laser treatment. This paper describes an approach to implement process monitoring and control for laser treatment of printed, nano-particulate ITO films.