Laser-induced birefringence in fused silica from polarized lasers

Ulrich Neukirch; Douglas C. Allan; Nicholas F. Borrelli; Christine E. Heckle; Michal Mlejnek; Johannes Moll; Charlene M. Smith

doi:10.1117/12.598741

12 May 2005 Laser-induced birefringence in fused silica from polarized lasers

Ulrich Neukirch, Douglas C. Allan, Nicholas F. Borrelli, Christine E. Heckle, Michal Mlejnek, Johannes Moll, Charlene M. Smith

Author Affiliations +

Proceedings Volume 5754, Optical Microlithography XVIII; (2005) https://doi.org/10.1117/12.598741
Event: Microlithography 2005, 2005, San Jose, California, United States

Abstract

Fused silica, when exposed to excimer laser light, exhibits permanent anisotropic birefringence and wavefront changes. These laser-induced changes depend on the silica composition and processing conditions. The optical anisotropy is most clearly observed in samples that are exposed with linear polarization. This polarization-induced effect has been known for several years, but has become much more important with the advent of immersion lithography and its associated very high numerical apertures. High numerical aperture optics require controlled polarization, notably linear polarization, in order to maintain phase contrast at the image. When birefringence and wavefront changes are induced by laser exposure, the image contrast at the wafer deteriorates. We interpret the changes in optical properties in terms of permanent anisotropic strain induced by laser damage, and the associated strain-induced optical effects. This is accomplished using the mathematics of tensors to account for anisotropic strain and optical anisotropy, and using finite element analysis to calculate the strain fields taking the sample and exposure geometries into account. We report the relations between underlying density and strain anisotropy changes and the induced birefringence and wavefront for a given experimental sample geometry. We also report some examples of the different degree of laser damage from silica with different compositions and processing conditions.

Citation Download Citation

Ulrich Neukirch, Douglas C. Allan, Nicholas F. Borrelli, Christine E. Heckle, Michal Mlejnek, Johannes Moll, and Charlene M. Smith "Laser-induced birefringence in fused silica from polarized lasers", Proc. SPIE 5754, Optical Microlithography XVIII, (12 May 2005); https://doi.org/10.1117/12.598741

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