Surface roughness of NaCl coating used as release layers in thin film production

Abstract

Surface roughness scans of NaCl (salt) coatings on silicon wafers were carried out using an Atomic Force Microscope. Metrology was carried out on single layer salt and also salt coated with a thin aluminium layer which is a representative high power laser target. All were characterised straight from vacuum and again after being exposed to the atmosphere for a few days. Results suggest that the surface roughness increased drastically after being left in atmospheric conditions for few days. The roughness increased by almost five time for an exposed salt coating. For a salt coating with an aluminium layer the roughness only increased slightly (∼1nm). This suggests that it’s important to coat materials for the laser target on to salt release layers almost immediately from vacuum. This work enables production processes and quality control for high power laser targets to be defined and an understanding of possible pinhole production in thin film coatings.