Rob Snijkers: Plasma etching and plasma display panels
My first introduction to the Group EPG was in 1987. I was looking for a research topic for my second traineeship and found this in the group EPG of professor Frits de Hoog, the predecessor of Gerrit Kroesen. I investigated the optogalvanic effect in a Townsend discharge, a fundamental topic of personal interest of Frits de Hoog. Due to changing locally the density of metastable particles in the discharge due to additional excitation processes by laser photons, the discharge characteristics (voltage and current) are changed.
The research made fun (nice topic, nice group, good atmosphere,…) and quite some work had to be done, so that I decided to extend the work to my graduation project.
The mechanisms behind these changes have been investigated and found. Therefore several old discharge tubes from 'ancient times' with all different fillings of gases and pressures and that were stored in the basement were brought to life (light!) again; but also some new tubes were made. A dye laser that was 'out of service' was re-activated and used to tune the right laser wavelength for the photoexcitation. The results were published and presented at an international conference by Frits de Hoog and by myself at the Lunteren-conference.
Just before Christmas 1988 I graduated but in January 1989 I continued working in EPG: I liked the research and got the opportunity for a Ph.D. For my Ph.D. I studied the energy distribution of ions in the sheath of a 13.56 MHz RF plasma in Ar and CF4. This has been done experimentally and theoretically.
To measure the energy distribution, I build a set up to measure for different ion species the energy at the grounded and driven electrode: so mass and energy selecting. It took quite some time to get the set up operational but in the last month of my Ph.D. I was able to collect a huge number of distributions for several discharge conditions to easily fill my Ph.D. thesis.
To determine the distribution theoretically I build a Monte Carlo simulation tool. This has been done together with the Theoretical Physics department of professor Sluiter.
The nice part was that the simulated distributions corresponded well with the measured ones and from the simulations we understood very well what happened in the sheath and how the energy distribution was build up. This insight helped to optimize the etching process as used in the semiconductor industry.
After my Ph.D. I worked for another 2,5 years in EPG. I studied micro discharges that were used in display technologies (plasma display panels, plasma addressed LCD panels). This research was paid by and upon instruction from Philips research. In 1996 I joined Philips research (in Aachen) after some very nice and instructive years in EPG.
Currently I work for Philips Lighting responsible for the predevelopment program of LED lighting systems.
Rob Snijkers, August 2011