Optimization of thickness uniformity in large area coatings using ion assisted electron beam evaporation: Numerical and experimental investigation

Achieving highly uniform thin film coatings over the large area is a critical technological challenge in the fabrication of high-performance x-ray mirrors. The coating thickness nonuniformity in an indigenously developed ultrahigh vacuum ion-assisted electron beam evaporation system equipped with a substrate rotation subsystem is systematically investigated through combined numerical simulations and experiments for rotating flat and curve substrates. The effects of substrate height, source offset, and substrate curvature on the thickness distribution profile are analyzed. Ni thin film samples are coated on small Si substrates distributed over 300 × 100 mm2 area for thickness distribution and microstructure analysis. A thickness nonuniformity of ∼3.17% is achieved with corresponding maximum coating induced slope error of ∼25 nrad across the length of a 300 mm flat surface. For the rotating cylindrical curved surface having a radius of curvature of 500 mm, the measured thickness nonuniformity decreases to ∼1.87%, with corresponding maximum slope error arises due to coating nonuniformity of ∼18 nrad across the length of 300 mm. This study provides practical design guidelines for deposition systems aimed at achieving highly uniform large area coatings.