4 August 1993 Lithographic effects of metal reflectivity variations
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This paper examines the effects of specular and diffuse reflectivities, both empirically and theoretically, on the imaging process for highly reflective substrates. Aluminum (Al) and Titanium Nitride (TiN) wafers were used extensively in this study. TiN wafers were prepared with varying specular reflectivities and virtually no diffuse reflectivity. Dose to clear on TiN wafers was found to increase linearly with specular reflectivity in the absence of any diffuse component. Aluminum wafers were prepared with high specular reflectivity and varying diffuse reflectivities. On these Al wafers, the increase in diffuse reflectivity decreased the dose to clear in a nonlinear fashion. A theoretical explanation for the observed phenomenon is presented based on the interaction of thin film interference effects with diffuse scattering. Modelling results based on this theory are shown to be in good agreement with the experimentally observed data. Based on these results, a method for the generation of specification limits for the allowable variations in specular and diffuse reflectivities are also presented. Also discussed are the tools and methods used for measuring substrate reflectivity to obtain these specification limits.
© (1993) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Nathan S. Thane, Chris A. Mack, Satyendra S. Sethi, "Lithographic effects of metal reflectivity variations", Proc. SPIE 1926, Integrated Circuit Metrology, Inspection, and Process Control VII, (4 August 1993); doi: 10.1117/12.148978; https://doi.org/10.1117/12.148978

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