CONTROLLED STRUCTURING OF SELF-ASSEMBLED POLYSTYRENE MICROSPHERE ARRAYS BY TWO DIFFERENT PLASMA SYSTEMS

Nanosphere lithography is a simple and time-efficient technique which is often recognized as an alternative to conventional top-down approaches standardly used in nanofabrication. In this study we present a successful manipulation of microspheres by reactive ion etching (RIE). A self-assembled monolayer close-packed array of monodisperse polystyrene microspheres (PM) with diameter of 471 nm was used as the primary template. The PM templates were processed in two different RIE systems: (i) capacitively coupled radiofrequency plasma (CCP) and (ii) dual plasma system which combines CCP and pulsed linear-antenna microwave plasma (PLAMWP). The influence of process conditions on the PM geometry was systematically studied by scanning electron microscopy (SEM). The process conditions were controlled by varying radiofrequency (RF) power, gas mixture (O-2:CF4 ratio) and process duration. A clear correlation between RIE conditions and the final PM geometry is found. In comparison to CCP-RIE, the PLAMWP system is less aggressive due to different plasma character and it allows smoother etching steps, thanks to which some conditions led to formation of long necks toward adjacent spheres. It was found out that choosing optimal parameters results in a tunable diameter of PM with various shapes (from spheres to pyramid-like structures) while keeping their periodic hexagonal ordering.