Photolithography is the engine that empowered microelectronics and semiconductor industry for more than 50 years. Photolithography allows building very complex micro- and nanostructures by copying a pattern from a photomask to a wafer. Photolithography is the key enabling technology (KET) behind the powerful concept of “shrinkage”, also referred to as “die shrink”, the ability to reduce the minimum feature size of transistors, electronic wires and other components of a microchip from some 50 microns in the early 1960s to some tens of nanometers today. Die shrink allows manufacturing more chips on a wafer, reducing manufacturing costs, minimizing the power consumption and improving the performance in terms of speed, storage capacity and customer convenience. Planar micro-optical elements play a decisive role in modern photolithography systems, e.g. for line width narrowing, laser beam shaping (customized illumination), phase-shift masks (PSM), optical proximity correction (OPC), diffraction-based overlay (DBO). In a holistic approach, modern photolithography uses precise shaping of the illumination light in combination with optimized phase-shift masks, referred to as source-mask optimization (SMO), to minimize diffraction effects and residual aberrations in the projection optics.
This paper summarizes the development of planar micro-optics from the invention of a computer-generated hologram (CGH) in the 1960s towards today’s wafer-based manufacturing of high-quality refractive and diffractive planar micro-optical elements. The manufacturing of planar micro-optics on wafer-level and the applications in modern projection lithography systems will be explained.
© 2015 Optical Society of AmericaPDF Article