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Practical Characterization Of 0.5 μm Optical Lithography

This paper establishes the characterization techniques that are needed to repeatedly fabricate submicron structures which are below the resolution specifications of an optical system. A two-parameter system is defined, consisting of a material or photosensitive component and an optical component, which represents the major contributors to process variability. Statistical inference and correlation analysis are used to estimate the effects and extent of the individual components on the total lithographic system. The photosensitive component, consisting of the photoresist, films and related chemistry, is shown to substantially represent the variability in the final linewidth of 0.5 μm structures. Positive and negative photoresist systems are compared and analyzed for run-to-run and within-run variability utilizing photoresist speed-point analysis. The optical component is explained by using a two-dimensional aerial image model which takes as input the numerical aperture, wavelength, coherence, aberrations and experimentally measured effects. A method for quantitatively measuring flare or background exposure is introduced.