Microfabrication of 3D structures by projection optical system

Three-dimensional (3D) patterns are often fabricated by the lamination of 3D printers although there are many problems for the manufacturing of micro-patterns. Optical lithography methods such as an aligner and a stepper has been used not only for the fabrication of two-dimensional (2D) micro-patterns including semiconductor integrated circuits but also for the manufacturing of 3D micro-patterns such as MEMS (Micro Electro Mechanical Systems). Especially, the pattern exposure by the optical projection system in a stepper enables both smaller micro-patterns by its high resolution and manufacturing by its one-shot exposure. The resolving power of the projection optics is mainly defined by the numerical aperture (NA) and the depth of focus (DOF). Especially for the fabrication of 3D patterns, DOF is the basic parameter showing the patterning ability of the height. In this study, we present the exposure method and the optical performance of micro-lens arrays (MLA) with step heights as high as 100μm by controlling the NA of the projection optical system. Since 3D integrated circuits often require fabricating patterns on its sidewall, we also present a fabrication method of exposure patterns to the sidewall of 3D micro-structures by controlling the aperture stop of illumination system in front of the projection optics.