Compact ultraviolet light-emitting diode-based lithography illumination system with tunable coherent factor

Optimization of the illumination system of an ultraviolet light-emitting diode (UVLED)-based lithography system by reducing the system complexity and spatial volume has been a research focus. This work proposes a compact lithography illumination system that applies a specially designed embedded compound parabolic concentrator (ECPC) to replace the traditional collimation module and the zoom lenses module. The ECPC, comprised of two detachable parabolic surfaces, precisely collimates all light beams from the UVLED to a preset divergence angle of 6 deg and provides an adjustable lithography coherent factor. The final illumination system offers a square illumination field with a uniformity of up to 1.3% in the large coherent factor and a linearly adjustable numerical aperture in the range of 0.02 similar to 0.04. The final exposure result of 0.7 mu m based on the experiment setup further verifies the performance of the designed illumination system.