The optimization of illumination in optical lithography has been central to the progress toward λ/5 resolution now commonplace. The tailoring of source shapes to meet increasing demands of imaging has been commercially practiced for over twenty years. The influence of illumination in microscopy and micrography had been explored for centuries before an adequate description was developed in the late nineteenth century. By the mid-twentieth century, the mathematical foundation for the dependency of resolution on illumination was presented, leading to the parameterization of illumination through a partial coherence factor (σ). The role of partial coherence in microscopy, micrography, and microlithography has been critical to the extension of resolution in each of these fields and has allowed for the application of optical lithography toward sub-50nm resolution. Today, source customization, polarized illumination, and source/mask domain co-optimization have become critical tools used to achieve manufacturable lithography resolution at the edge of physical limits. This paper will provide a historical look into how illumination, partial coherence, and source shaping has influenced optical lithography. Aspects relative to future lithography generations are also explored, including illumination influences with 3D effects especially important for EUV wavelength applications.

Date Published: 4 April 2014
PDF: 9 pages
Proc. SPIE 9052, Optical Microlithography XXVII, 905204 (4 April 2014);

Published in SPIE Proceedings Vol. 9052:
Optical Microlithography XXVII
Kafai Lai; Andreas Erdmann, Editor(s)