Photoresist modification by silver colloid solution: the role of silver nanoparticles content
Proceedings of the Estonian Academy of Sciences
The aim of this work was to investigate the influence of silver nanoparticles deposited from a colloid solution into a photoresist composition on the morphology and optical properties of the grating. The Ag colloid was produced by chemical reduction of silver nitrate and incorporated in the photoresist composition by mixing. The film of Ag colloid solution modified photoresist was obtained by spin coating on an optical quartz substrate and dried at 100 °C for 20 min. The grating with a period
... ing with a period of 4 µm was formed by contact lithography. The synthesized Ag nanoparticles were spherical or roughly spherical with diameters varying from 10 nm up to 60 nm. The content of Ag nanoparticles in the photoresist rose from 0.02 wt% to 4.66 wt% when the concentration of the Ag colloid solution increased from 10 to 30 wt%. Analysis performed with atomic force microscope and scanning electron microscope showed that Ag nanoparticles changed geometrical parameters and optical properties of the gratings: their height decreased and diffraction efficiency increased in all orders. However, the increase of the Ag content up to 4.66 wt% considerably changed the grating geometry. In this case the ridges of the grating became concave, probably due to the Ag nanoparticles light diffusion. For this reason secondary reflections appeared during photolithography and the ridge of grating is affected by exposure. Therefore the ridge surface becomes soluble to etching solvents, and exposure areas are removed.