A typical zone plate structure is composed of concentric rings with a radially decreasing feature size such that the path of light through every second zone to the focus differs by one optical wavelength. In order to achieve the highest possible diffraction efficiency, etching depth has to be controlled uniformly across the whole substrate area to a phase difference of half wavelength between adjacent zones. In this study, an optimized plasma etching process has been developed to minimize the feature size variation effect and a Teflon ring has been made to eliminate the edge effect on thick fused silica. Large phase type dual-focus zone plate with varied concentric ring sizes good etching profile and better than 2% etching depth uniformity was successfully made.
Citation: Microelectronic Engineering
Pub Type: Journals