5 July 2000 Modeling oblique incidence effects in photomasks
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Abstract
As mask features scale to smaller dimensions, the so-called 'vertical effects' which, to present, have mostly been neglected, become important. The usual assumption of constant scattering coefficients for different angles of incidence needs to be reconsidered as the aspect ratio of mask features increases. The use of higher NA systems introduces high obliquity field components that further compound the problem. Rigorous electromagnetic simulation is used to investigate the scattering properties of various lithographic masks. Scattering coefficients are calculated and compared for the classical binary mask, masks with OPC features and phase-shifting masks under wafer printing and inspection conditions. Specific attention is paid to quantifying the limitations of the constant scattering coefficient assumption. An efficient scheme to calculate aerial images in situations with non-constant scattering coefficients is presented. Aerial images calculated with this scheme are compared to aerial images calculated under the constant scattering coefficient assumption. Binary mask with and without OPC are shown to not exhibit scattering dependence on angle of incidence. Phase shift masks require rigorous electromagnetic simulation and some, such as the dual trench, exhibit moderate scattering scattering dependence on the angle of incidence must be considered because of the high angles involved. A tabulated summary of mask simulation is presented in the conclusion.
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Thomas V. Pistor, Thomas V. Pistor, Andrew R. Neureuther, Andrew R. Neureuther, Robert John Socha, Robert John Socha, } "Modeling oblique incidence effects in photomasks", Proc. SPIE 4000, Optical Microlithography XIII, (5 July 2000); doi: 10.1117/12.389012; https://doi.org/10.1117/12.389012
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