Deep-UV photolithography linewidth variation from reflective substrates

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Abstract
Thin-film interference effects change the fraction of energy available for absorption in the photoresist, resulting directly in linewidth changes. This paper addresses the absorbed energy variation due to the variation in films underlying the photoresist. An optical thin-film interference model is developed and compared to measured reflectivity data for continuously varying silicon nitride under DUV positive photoresist. The model is used to predict an improved linewidth control of greater than a factor of three for broadband over monochromatic illumination, which is also experimentally verified. In addition, simulated and measured data are presented with and without an antireflective coating underlying the resist.

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